[40/46] cxl/region: Attach endpoint decoders

CXL regions (interleave sets) are made up of a set of memory devices
where each device maps a portion of the interleave with one of its
decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
As endpoint decoders are identified by a provisioning tool they can be
added to a region provided the region interleave properties are set
(way, granularity, HPA) and DPA has been assigned to the decoder.

The attach event triggers several validation checks, for example:
- is the DPA sized appropriately for the region
- is the decoder reachable via the host-bridges identified by the
  region's root decoder
- is the device already active in a different region position slot
- are there already regions with a higher HPA active on a given port
  (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)

...and the attach event affords an opportunity to collect data and
resources relevant to later programming the target lists in switch
decoders, for example:
- allocate a decoder at each cxl_port in the decode chain
- for a given switch port, how many the region's endpoints are hosted
  through the port
- how many unique targets (next hops) does a port need to map to reach
  those endpoints

The act of reconciling this information and deploying it to the decoder
configuration is saved for a follow-on patch.

Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/cxl/core/core.h   |   7 +
 drivers/cxl/core/port.c   |  10 +-
 drivers/cxl/core/region.c | 338 +++++++++++++++++++++++++++++++++++++-
 drivers/cxl/cxl.h         |  20 +++
 drivers/cxl/cxlmem.h      |   5 +
 5 files changed, 372 insertions(+), 8 deletions(-)

On Thu, 23 Jun 2022 21:19:44 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> CXL regions (interleave sets) are made up of a set of memory devices
> where each device maps a portion of the interleave with one of its
> decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
> As endpoint decoders are identified by a provisioning tool they can be
> added to a region provided the region interleave properties are set
> (way, granularity, HPA) and DPA has been assigned to the decoder.
> 
> The attach event triggers several validation checks, for example:
> - is the DPA sized appropriately for the region
> - is the decoder reachable via the host-bridges identified by the
>   region's root decoder
> - is the device already active in a different region position slot
> - are there already regions with a higher HPA active on a given port
>   (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)
> 
> ...and the attach event affords an opportunity to collect data and
> resources relevant to later programming the target lists in switch
> decoders, for example:
> - allocate a decoder at each cxl_port in the decode chain
> - for a given switch port, how many the region's endpoints are hosted
>   through the port
> - how many unique targets (next hops) does a port need to map to reach
>   those endpoints
> 
> The act of reconciling this information and deploying it to the decoder
> configuration is saved for a follow-on patch.
Hi Dam,
n
Only managed to grab a few mins today to debug that crash.. So I know
the immediate cause but not yet why we got to that state.

Test case (happened to be one I had open) is 2x HB, 2x RP on each,
direct connected type 3s on all ports.

Manual test script is:

insmod modules/5.19.0-rc3+/kernel/drivers/cxl/core/cxl_core.ko
insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_acpi.ko
insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_port.ko
insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pci.ko
insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_mem.ko
insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pmem.ko

cd /sys/bus/cxl/devices/decoder0.0/
cat create_pmem_region
echo region0 > create_pmem_region

cd region0/
echo 4 > interleave_ways
echo $((256 << 22)) > size
echo 6a6b9b22-e0d4-11ec-9d64-0242ac120002 > uuid
ls -lh /sys/bus/cxl/devices/endpoint?/upo*

# Then figure out the order hopefully write the correct targets 
echo decoder5.0 > target0

Location of crash below...
No idea if these breadcrumbs will be much use. I'll poke
it some more next week. Have a good weekend,

Jonathan


> 
> Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
> Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/cxl/core/core.h   |   7 +
>  drivers/cxl/core/port.c   |  10 +-
>  drivers/cxl/core/region.c | 338 +++++++++++++++++++++++++++++++++++++-
>  drivers/cxl/cxl.h         |  20 +++
>  drivers/cxl/cxlmem.h      |   5 +
>  5 files changed, 372 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
> index 36b6bd8dac2b..0e4e5c2d9452 100644
> --- a/drivers/cxl/core/core.h
> +++ b/drivers/cxl/core/core.h
> @@ -42,6 +42,13 @@ resource_size_t cxl_dpa_size(struct cxl_endpoint_decoder *cxled);
>  resource_size_t cxl_dpa_resource(struct cxl_endpoint_decoder *cxled);
>  extern struct rw_semaphore cxl_dpa_rwsem;
>  
> +bool is_switch_decoder(struct device *dev);
> +static inline struct cxl_ep *cxl_ep_load(struct cxl_port *port,
> +					 struct cxl_memdev *cxlmd)
> +{
> +	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
> +}
> +
>  int cxl_memdev_init(void);
>  void cxl_memdev_exit(void);
>  void cxl_mbox_init(void);
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 7756409d0a58..fde2a2e103d4 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -447,7 +447,7 @@ bool is_root_decoder(struct device *dev)
>  }
>  EXPORT_SYMBOL_NS_GPL(is_root_decoder, CXL);
>  
> -static bool is_switch_decoder(struct device *dev)
> +bool is_switch_decoder(struct device *dev)
>  {
>  	return is_root_decoder(dev) || dev->type == &cxl_decoder_switch_type;
>  }
> @@ -503,6 +503,7 @@ static void cxl_port_release(struct device *dev)
>  		cxl_ep_remove(port, ep);
>  	xa_destroy(&port->endpoints);
>  	xa_destroy(&port->dports);
> +	xa_destroy(&port->regions);
>  	ida_free(&cxl_port_ida, port->id);
>  	kfree(port);
>  }
> @@ -633,6 +634,7 @@ static struct cxl_port *cxl_port_alloc(struct device *uport,
>  	port->dpa_end = -1;
>  	xa_init(&port->dports);
>  	xa_init(&port->endpoints);
> +	xa_init(&port->regions);
>  
>  	device_initialize(dev);
>  	lockdep_set_class_and_subclass(&dev->mutex, &cxl_port_key, port->depth);
> @@ -1110,12 +1112,6 @@ static void reap_dports(struct cxl_port *port)
>  	}
>  }
>  
> -static struct cxl_ep *cxl_ep_load(struct cxl_port *port,
> -				  struct cxl_memdev *cxlmd)
> -{
> -	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
> -}
> -
>  int devm_cxl_add_endpoint(struct cxl_memdev *cxlmd,
>  			  struct cxl_dport *parent_dport)
>  {
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 4830365f3857..65bf84abad57 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -428,6 +428,254 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
>  	return rc;
>  }
>  
> +static int match_free_decoder(struct device *dev, void *data)
> +{
> +	struct cxl_decoder *cxld;
> +	int *id = data;
> +
> +	if (!is_switch_decoder(dev))
> +		return 0;
> +
> +	cxld = to_cxl_decoder(dev);
> +
> +	/* enforce ordered allocation */
> +	if (cxld->id != *id)
> +		return 0;
> +
> +	if (!cxld->region)
> +		return 1;
> +
> +	(*id)++;
> +
> +	return 0;
> +}
> +
> +static struct cxl_decoder *cxl_region_find_decoder(struct cxl_port *port,
> +						   struct cxl_region *cxlr)
> +{
> +	struct device *dev;
> +	int id = 0;
> +
> +	dev = device_find_child(&port->dev, &id, match_free_decoder);
> +	if (!dev)
> +		return NULL;
> +	/*
> +	 * This decoder is pinned registered as long as the endpoint decoder is
> +	 * registered, and endpoint decoder unregistration holds the
> +	 * cxl_region_rwsem over unregister events, so no need to hold on to
> +	 * this extra reference.
> +	 */
> +	put_device(dev);
> +	return to_cxl_decoder(dev);
> +}
> +
> +static struct cxl_region_ref *alloc_region_ref(struct cxl_port *port,
> +					       struct cxl_region *cxlr)
> +{
> +	struct cxl_region_ref *cxl_rr;
> +
> +	cxl_rr = kzalloc(sizeof(*cxl_rr), GFP_KERNEL);
> +	if (!cxl_rr)
> +		return NULL;
> +	cxl_rr->port = port;
> +	cxl_rr->region = cxlr;
> +	xa_init(&cxl_rr->endpoints);
> +	return cxl_rr;
> +}
> +
> +static void free_region_ref(struct cxl_region_ref *cxl_rr)
> +{
> +	struct cxl_port *port = cxl_rr->port;
> +	struct cxl_region *cxlr = cxl_rr->region;
> +	struct cxl_decoder *cxld = cxl_rr->decoder;
> +
> +	dev_WARN_ONCE(&cxlr->dev, cxld->region != cxlr, "region mismatch\n");
> +	if (cxld->region == cxlr) {
> +		cxld->region = NULL;
> +		put_device(&cxlr->dev);
> +	}
> +
> +	xa_erase(&port->regions, (unsigned long)cxlr);
> +	xa_destroy(&cxl_rr->endpoints);
> +	kfree(cxl_rr);
> +}
> +
> +static int cxl_rr_add(struct cxl_region_ref *cxl_rr)
> +{
> +	struct cxl_port *port = cxl_rr->port;
> +	struct cxl_region *cxlr = cxl_rr->region;
> +
> +	return xa_insert(&port->regions, (unsigned long)cxlr, cxl_rr,
> +			 GFP_KERNEL);
> +}
> +
> +static int cxl_rr_ep_add(struct cxl_region_ref *cxl_rr,
> +			 struct cxl_endpoint_decoder *cxled)
> +{
> +	int rc;
> +	struct cxl_port *port = cxl_rr->port;
> +	struct cxl_region *cxlr = cxl_rr->region;
> +	struct cxl_decoder *cxld = cxl_rr->decoder;
> +	struct cxl_ep *ep = cxl_ep_load(port, cxled_to_memdev(cxled));
> +
> +	rc = xa_insert(&cxl_rr->endpoints, (unsigned long)cxled, ep,
> +			 GFP_KERNEL);
> +	if (rc)
> +		return rc;
> +	cxl_rr->nr_eps++;
> +
> +	if (!cxld->region) {
> +		cxld->region = cxlr;
> +		get_device(&cxlr->dev);
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_port_attach_region(struct cxl_port *port,
> +				  struct cxl_region *cxlr,
> +				  struct cxl_endpoint_decoder *cxled, int pos)
> +{
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_ep *ep = cxl_ep_load(port, cxlmd);
> +	struct cxl_region_ref *cxl_rr = NULL, *iter;
> +	struct cxl_region_params *p = &cxlr->params;
> +	struct cxl_decoder *cxld = NULL;
> +	unsigned long index;
> +	int rc = -EBUSY;
> +
> +	lockdep_assert_held_write(&cxl_region_rwsem);
> +
> +	xa_for_each(&port->regions, index, iter) {
> +		struct cxl_region_params *ip = &iter->region->params;
> +
> +		if (iter->region == cxlr)
> +			cxl_rr = iter;
> +		if (ip->res->start > p->res->start) {
> +			dev_dbg(&cxlr->dev,
> +				"%s: HPA order violation %s:%pr vs %pr\n",
> +				dev_name(&port->dev),
> +				dev_name(&iter->region->dev), ip->res, p->res);
> +			return -EBUSY;
> +		}
> +	}
> +
> +	if (cxl_rr) {
> +		struct cxl_ep *ep_iter;
> +		int found = 0;
> +
> +		cxld = cxl_rr->decoder;
> +		xa_for_each(&cxl_rr->endpoints, index, ep_iter) {
> +			if (ep_iter == ep)
> +				continue;
> +			if (ep_iter->next == ep->next) {
> +				found++;
> +				break;
> +			}
> +		}
> +
> +		/*
> +		 * If this is a new target or if this port is direct connected
> +		 * to this endpoint then add to the target count.
> +		 */
> +		if (!found || !ep->next)
> +			cxl_rr->nr_targets++;
> +	} else {
> +		cxl_rr = alloc_region_ref(port, cxlr);
> +		if (!cxl_rr) {
> +			dev_dbg(&cxlr->dev,
> +				"%s: failed to allocate region reference\n",
> +				dev_name(&port->dev));
> +			return -ENOMEM;
> +		}
> +		rc = cxl_rr_add(cxl_rr);
> +		if (rc) {
> +			dev_dbg(&cxlr->dev,
> +				"%s: failed to track region reference\n",
> +				dev_name(&port->dev));
> +			kfree(cxl_rr);
> +			return rc;
> +		}
> +	}
> +
> +	if (!cxld) {
> +		if (port == cxled_to_port(cxled))
> +			cxld = &cxled->cxld;
> +		else
> +			cxld = cxl_region_find_decoder(port, cxlr);
> +		if (!cxld) {
> +			dev_dbg(&cxlr->dev, "%s: no decoder available\n",
> +				dev_name(&port->dev));
> +			goto out_erase;
> +		}
> +
> +		if (cxld->region) {
> +			dev_dbg(&cxlr->dev, "%s: %s already attached to %s\n",
> +				dev_name(&port->dev), dev_name(&cxld->dev),
> +				dev_name(&cxld->region->dev));
> +			rc = -EBUSY;
> +			goto out_erase;
> +		}
> +
> +		cxl_rr->decoder = cxld;
> +	}
> +
> +	rc = cxl_rr_ep_add(cxl_rr, cxled);
> +	if (rc) {
> +		dev_dbg(&cxlr->dev,
> +			"%s: failed to track endpoint %s:%s reference\n",
> +			dev_name(&port->dev), dev_name(&cxlmd->dev),
> +			dev_name(&cxld->dev));
> +		goto out_erase;
> +	}
> +
> +	return 0;
> +out_erase:
> +	if (cxl_rr->nr_eps == 0)
> +		free_region_ref(cxl_rr);
> +	return rc;
> +}
> +
> +static struct cxl_region_ref *cxl_rr_load(struct cxl_port *port,
> +					  struct cxl_region *cxlr)
> +{
> +	return xa_load(&port->regions, (unsigned long)cxlr);
> +}
> +
> +static void cxl_port_detach_region(struct cxl_port *port,
> +				   struct cxl_region *cxlr,
> +				   struct cxl_endpoint_decoder *cxled)
> +{
> +	struct cxl_region_ref *cxl_rr;
> +	struct cxl_ep *ep;
> +
> +	lockdep_assert_held_write(&cxl_region_rwsem);
> +
> +	cxl_rr = cxl_rr_load(port, cxlr);
> +	if (!cxl_rr)
> +		return;
> +
> +	ep = xa_erase(&cxl_rr->endpoints, (unsigned long)cxled);
> +	if (ep) {
> +		struct cxl_ep *ep_iter;
> +		unsigned long index;
> +		int found = 0;
> +
> +		cxl_rr->nr_eps--;
> +		xa_for_each(&cxl_rr->endpoints, index, ep_iter) {
> +			if (ep_iter->next == ep->next) {
> +				found++;
> +				break;
> +			}
> +		}
> +		if (!found)
> +			cxl_rr->nr_targets--;
> +	}
> +
> +	if (cxl_rr->nr_eps == 0)
> +		free_region_ref(cxl_rr);
> +}
> +
>  /*
>   * - Check that the given endpoint is attached to a host-bridge identified
>   *   in the root interleave.
> @@ -435,14 +683,28 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
>  static int cxl_region_attach(struct cxl_region *cxlr,
>  			     struct cxl_endpoint_decoder *cxled, int pos)
>  {
> +	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_port *ep_port, *root_port, *iter;
>  	struct cxl_region_params *p = &cxlr->params;
> +	struct cxl_dport *dport;
> +	int i, rc = -ENXIO;
>  
>  	if (cxled->mode == CXL_DECODER_DEAD) {
>  		dev_dbg(&cxlr->dev, "%s dead\n", dev_name(&cxled->cxld.dev));
>  		return -ENODEV;
>  	}
>  
> -	if (pos >= p->interleave_ways) {
> +	/* all full of members, or interleave config not established? */
> +	if (p->state > CXL_CONFIG_INTERLEAVE_ACTIVE) {
> +		dev_dbg(&cxlr->dev, "region already active\n");
> +		return -EBUSY;
> +	} else if (p->state < CXL_CONFIG_INTERLEAVE_ACTIVE) {
> +		dev_dbg(&cxlr->dev, "interleave config missing\n");
> +		return -ENXIO;
> +	}
> +
> +	if (pos < 0 || pos >= p->interleave_ways) {
>  		dev_dbg(&cxlr->dev, "position %d out of range %d\n", pos,
>  			p->interleave_ways);
>  		return -ENXIO;
> @@ -461,15 +723,83 @@ static int cxl_region_attach(struct cxl_region *cxlr,
>  		return -EBUSY;
>  	}
>  
> +	for (i = 0; i < p->interleave_ways; i++) {
> +		struct cxl_endpoint_decoder *cxled_target;
> +		struct cxl_memdev *cxlmd_target;
> +
> +		cxled_target = p->targets[pos];
> +		if (!cxled_target)
> +			continue;
> +
> +		cxlmd_target = cxled_to_memdev(cxled_target);
> +		if (cxlmd_target == cxlmd) {
> +			dev_dbg(&cxlr->dev,
> +				"%s already specified at position %d via: %s\n",
> +				dev_name(&cxlmd->dev), pos,
> +				dev_name(&cxled_target->cxld.dev));
> +			return -EBUSY;
> +		}
> +	}
> +
> +	ep_port = cxled_to_port(cxled);
> +	root_port = cxlrd_to_port(cxlrd);
> +	dport = cxl_dport_load(root_port, ep_port->host_bridge);
> +	if (!dport) {
> +		dev_dbg(&cxlr->dev, "%s:%s invalid target for %s\n",
> +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> +			dev_name(cxlr->dev.parent));
> +		return -ENXIO;
> +	}
> +
> +	if (cxlrd->calc_hb(cxlrd, pos) != dport) {
> +		dev_dbg(&cxlr->dev, "%s:%s invalid target position for %s\n",
> +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> +			dev_name(&cxlrd->cxlsd.cxld.dev));
> +		return -ENXIO;
> +	}
> +
> +	if (cxled->cxld.target_type != cxlr->type) {
> +		dev_dbg(&cxlr->dev, "%s:%s type mismatch: %d vs %d\n",
> +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> +			cxled->cxld.target_type, cxlr->type);
> +		return -ENXIO;
> +	}
> +
> +	if (resource_size(cxled->dpa_res) * p->interleave_ways !=

At this point cxled->dpa_res is NULL.

> +	    resource_size(p->res)) {
> +		dev_dbg(&cxlr->dev,
> +			"decoder-size-%#llx * ways-%d != region-size-%#llx\n",
> +			(u64)resource_size(cxled->dpa_res), p->interleave_ways,
> +			(u64)resource_size(p->res));
> +		return -EINVAL;
> +	}
> +
> +	for (iter = ep_port; !is_cxl_root(iter);
> +	     iter = to_cxl_port(iter->dev.parent)) {
> +		rc = cxl_port_attach_region(iter, cxlr, cxled, pos);
> +		if (rc)
> +			goto err;
> +	}
> +
>  	p->targets[pos] = cxled;
>  	cxled->pos = pos;
>  	p->nr_targets++;
>  
> +	if (p->nr_targets == p->interleave_ways)
> +		p->state = CXL_CONFIG_ACTIVE;
> +
>  	return 0;
> +
> +err:
> +	for (iter = ep_port; !is_cxl_root(iter);
> +	     iter = to_cxl_port(iter->dev.parent))
> +		cxl_port_detach_region(iter, cxlr, cxled);
> +	return rc;
>  }
>  
>  static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  {
> +	struct cxl_port *iter, *ep_port = cxled_to_port(cxled);
>  	struct cxl_region *cxlr = cxled->cxld.region;
>  	struct cxl_region_params *p;
>  
> @@ -481,6 +811,10 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  	p = &cxlr->params;
>  	get_device(&cxlr->dev);
>  
> +	for (iter = ep_port; !is_cxl_root(iter);
> +	     iter = to_cxl_port(iter->dev.parent))
> +		cxl_port_detach_region(iter, cxlr, cxled);
> +
>  	if (cxled->pos < 0 || cxled->pos >= p->interleave_ways ||
>  	    p->targets[cxled->pos] != cxled) {
>  		struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> @@ -491,6 +825,8 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  		goto out;
>  	}
>  
> +	if (p->state == CXL_CONFIG_ACTIVE)
> +		p->state = CXL_CONFIG_INTERLEAVE_ACTIVE;
>  	p->targets[cxled->pos] = NULL;
>  	p->nr_targets--;
>  
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 30227348f768..09dbd46cc4c7 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -414,6 +414,7 @@ struct cxl_nvdimm {
>   * @id: id for port device-name
>   * @dports: cxl_dport instances referenced by decoders
>   * @endpoints: cxl_ep instances, endpoints that are a descendant of this port
> + * @regions: cxl_region_ref instances, regions mapped by this port
>   * @parent_dport: dport that points to this port in the parent
>   * @decoder_ida: allocator for decoder ids
>   * @dpa_end: cursor to track highest allocated decoder for allocation ordering
> @@ -428,6 +429,7 @@ struct cxl_port {
>  	int id;
>  	struct xarray dports;
>  	struct xarray endpoints;
> +	struct xarray regions;
>  	struct cxl_dport *parent_dport;
>  	struct ida decoder_ida;
>  	int dpa_end;
> @@ -470,6 +472,24 @@ struct cxl_ep {
>  	struct cxl_port *next;
>  };
>  
> +/**
> + * struct cxl_region_ref - track a region's interest in a port
> + * @port: point in topology to install this reference
> + * @decoder: decoder assigned for @region in @port
> + * @region: region for this reference
> + * @endpoints: cxl_ep references for region members beneath @port
> + * @nr_eps: number of endpoints beneath @port
> + * @nr_targets: number of distinct targets needed to reach @nr_eps
> + */
> +struct cxl_region_ref {
> +	struct cxl_port *port;
> +	struct cxl_decoder *decoder;
> +	struct cxl_region *region;
> +	struct xarray endpoints;
> +	int nr_eps;
> +	int nr_targets;
> +};
> +
>  /*
>   * The platform firmware device hosting the root is also the top of the
>   * CXL port topology. All other CXL ports have another CXL port as their
> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> index eee96016c3c7..a83bb6782d23 100644
> --- a/drivers/cxl/cxlmem.h
> +++ b/drivers/cxl/cxlmem.h
> @@ -55,6 +55,11 @@ static inline struct cxl_port *cxled_to_port(struct cxl_endpoint_decoder *cxled)
>  	return to_cxl_port(cxled->cxld.dev.parent);
>  }
>  
> +static inline struct cxl_port *cxlrd_to_port(struct cxl_root_decoder *cxlrd)
> +{
> +	return to_cxl_port(cxlrd->cxlsd.cxld.dev.parent);
> +}
> +
>  static inline struct cxl_memdev *
>  cxled_to_memdev(struct cxl_endpoint_decoder *cxled)
>  {

Jonathan Cameron wrote:
> On Thu, 23 Jun 2022 21:19:44 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
> 
> > CXL regions (interleave sets) are made up of a set of memory devices
> > where each device maps a portion of the interleave with one of its
> > decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
> > As endpoint decoders are identified by a provisioning tool they can be
> > added to a region provided the region interleave properties are set
> > (way, granularity, HPA) and DPA has been assigned to the decoder.
> > 
> > The attach event triggers several validation checks, for example:
> > - is the DPA sized appropriately for the region
> > - is the decoder reachable via the host-bridges identified by the
> >   region's root decoder
> > - is the device already active in a different region position slot
> > - are there already regions with a higher HPA active on a given port
> >   (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)
> > 
> > ...and the attach event affords an opportunity to collect data and
> > resources relevant to later programming the target lists in switch
> > decoders, for example:
> > - allocate a decoder at each cxl_port in the decode chain
> > - for a given switch port, how many the region's endpoints are hosted
> >   through the port
> > - how many unique targets (next hops) does a port need to map to reach
> >   those endpoints
> > 
> > The act of reconciling this information and deploying it to the decoder
> > configuration is saved for a follow-on patch.
> Hi Dam,
> n
> Only managed to grab a few mins today to debug that crash.. So I know
> the immediate cause but not yet why we got to that state.
> 
> Test case (happened to be one I had open) is 2x HB, 2x RP on each,
> direct connected type 3s on all ports.

Can you send along the QEMU startup script for this config as well?

> Manual test script is:
> 
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/core/cxl_core.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_acpi.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_port.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pci.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_mem.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pmem.ko

Yikes, nothing good ever came insmod, modprobe and automatically module
dependency handling is the way to go.

> 
> cd /sys/bus/cxl/devices/decoder0.0/
> cat create_pmem_region
> echo region0 > create_pmem_region
> 
> cd region0/
> echo 4 > interleave_ways
> echo $((256 << 22)) > size
> echo 6a6b9b22-e0d4-11ec-9d64-0242ac120002 > uuid
> ls -lh /sys/bus/cxl/devices/endpoint?/upo*
> 
> # Then figure out the order hopefully write the correct targets 
> echo decoder5.0 > target0
> 
> Location of crash below...
> No idea if these breadcrumbs will be much use. I'll poke
> it some more next week. Have a good weekend,
> 
> Jonathan
> 
> 
> > 
> > Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
> > Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > ---
> >  drivers/cxl/core/core.h   |   7 +
> >  drivers/cxl/core/port.c   |  10 +-
> >  drivers/cxl/core/region.c | 338 +++++++++++++++++++++++++++++++++++++-
> >  drivers/cxl/cxl.h         |  20 +++
> >  drivers/cxl/cxlmem.h      |   5 +
> >  5 files changed, 372 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
> > index 36b6bd8dac2b..0e4e5c2d9452 100644
> > --- a/drivers/cxl/core/core.h
> > +++ b/drivers/cxl/core/core.h
> > @@ -42,6 +42,13 @@ resource_size_t cxl_dpa_size(struct cxl_endpoint_decoder *cxled);
> >  resource_size_t cxl_dpa_resource(struct cxl_endpoint_decoder *cxled);
> >  extern struct rw_semaphore cxl_dpa_rwsem;
> >  
> > +bool is_switch_decoder(struct device *dev);
> > +static inline struct cxl_ep *cxl_ep_load(struct cxl_port *port,
> > +					 struct cxl_memdev *cxlmd)
> > +{
> > +	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
> > +}
> > +
> >  int cxl_memdev_init(void);
> >  void cxl_memdev_exit(void);
> >  void cxl_mbox_init(void);
> > diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> > index 7756409d0a58..fde2a2e103d4 100644
> > --- a/drivers/cxl/core/port.c
> > +++ b/drivers/cxl/core/port.c
> > @@ -447,7 +447,7 @@ bool is_root_decoder(struct device *dev)
> >  }
> >  EXPORT_SYMBOL_NS_GPL(is_root_decoder, CXL);
> >  
> > -static bool is_switch_decoder(struct device *dev)
> > +bool is_switch_decoder(struct device *dev)
> >  {
> >  	return is_root_decoder(dev) || dev->type == &cxl_decoder_switch_type;
> >  }
> > @@ -503,6 +503,7 @@ static void cxl_port_release(struct device *dev)
> >  		cxl_ep_remove(port, ep);
> >  	xa_destroy(&port->endpoints);
> >  	xa_destroy(&port->dports);
> > +	xa_destroy(&port->regions);
> >  	ida_free(&cxl_port_ida, port->id);
> >  	kfree(port);
> >  }
> > @@ -633,6 +634,7 @@ static struct cxl_port *cxl_port_alloc(struct device *uport,
> >  	port->dpa_end = -1;
> >  	xa_init(&port->dports);
> >  	xa_init(&port->endpoints);
> > +	xa_init(&port->regions);
> >  
> >  	device_initialize(dev);
> >  	lockdep_set_class_and_subclass(&dev->mutex, &cxl_port_key, port->depth);
> > @@ -1110,12 +1112,6 @@ static void reap_dports(struct cxl_port *port)
> >  	}
> >  }
> >  
> > -static struct cxl_ep *cxl_ep_load(struct cxl_port *port,
> > -				  struct cxl_memdev *cxlmd)
> > -{
> > -	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
> > -}
> > -
> >  int devm_cxl_add_endpoint(struct cxl_memdev *cxlmd,
> >  			  struct cxl_dport *parent_dport)
> >  {
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index 4830365f3857..65bf84abad57 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -428,6 +428,254 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
> >  	return rc;
> >  }
> >  
> > +static int match_free_decoder(struct device *dev, void *data)
> > +{
> > +	struct cxl_decoder *cxld;
> > +	int *id = data;
> > +
> > +	if (!is_switch_decoder(dev))
> > +		return 0;
> > +
> > +	cxld = to_cxl_decoder(dev);
> > +
> > +	/* enforce ordered allocation */
> > +	if (cxld->id != *id)
> > +		return 0;
> > +
> > +	if (!cxld->region)
> > +		return 1;
> > +
> > +	(*id)++;
> > +
> > +	return 0;
> > +}
> > +
> > +static struct cxl_decoder *cxl_region_find_decoder(struct cxl_port *port,
> > +						   struct cxl_region *cxlr)
> > +{
> > +	struct device *dev;
> > +	int id = 0;
> > +
> > +	dev = device_find_child(&port->dev, &id, match_free_decoder);
> > +	if (!dev)
> > +		return NULL;
> > +	/*
> > +	 * This decoder is pinned registered as long as the endpoint decoder is
> > +	 * registered, and endpoint decoder unregistration holds the
> > +	 * cxl_region_rwsem over unregister events, so no need to hold on to
> > +	 * this extra reference.
> > +	 */
> > +	put_device(dev);
> > +	return to_cxl_decoder(dev);
> > +}
> > +
> > +static struct cxl_region_ref *alloc_region_ref(struct cxl_port *port,
> > +					       struct cxl_region *cxlr)
> > +{
> > +	struct cxl_region_ref *cxl_rr;
> > +
> > +	cxl_rr = kzalloc(sizeof(*cxl_rr), GFP_KERNEL);
> > +	if (!cxl_rr)
> > +		return NULL;
> > +	cxl_rr->port = port;
> > +	cxl_rr->region = cxlr;
> > +	xa_init(&cxl_rr->endpoints);
> > +	return cxl_rr;
> > +}
> > +
> > +static void free_region_ref(struct cxl_region_ref *cxl_rr)
> > +{
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +	struct cxl_decoder *cxld = cxl_rr->decoder;
> > +
> > +	dev_WARN_ONCE(&cxlr->dev, cxld->region != cxlr, "region mismatch\n");
> > +	if (cxld->region == cxlr) {
> > +		cxld->region = NULL;
> > +		put_device(&cxlr->dev);
> > +	}
> > +
> > +	xa_erase(&port->regions, (unsigned long)cxlr);
> > +	xa_destroy(&cxl_rr->endpoints);
> > +	kfree(cxl_rr);
> > +}
> > +
> > +static int cxl_rr_add(struct cxl_region_ref *cxl_rr)
> > +{
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +
> > +	return xa_insert(&port->regions, (unsigned long)cxlr, cxl_rr,
> > +			 GFP_KERNEL);
> > +}
> > +
> > +static int cxl_rr_ep_add(struct cxl_region_ref *cxl_rr,
> > +			 struct cxl_endpoint_decoder *cxled)
> > +{
> > +	int rc;
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +	struct cxl_decoder *cxld = cxl_rr->decoder;
> > +	struct cxl_ep *ep = cxl_ep_load(port, cxled_to_memdev(cxled));
> > +
> > +	rc = xa_insert(&cxl_rr->endpoints, (unsigned long)cxled, ep,
> > +			 GFP_KERNEL);
> > +	if (rc)
> > +		return rc;
> > +	cxl_rr->nr_eps++;
> > +
> > +	if (!cxld->region) {
> > +		cxld->region = cxlr;
> > +		get_device(&cxlr->dev);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int cxl_port_attach_region(struct cxl_port *port,
> > +				  struct cxl_region *cxlr,
> > +				  struct cxl_endpoint_decoder *cxled, int pos)
> > +{
> > +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> > +	struct cxl_ep *ep = cxl_ep_load(port, cxlmd);
> > +	struct cxl_region_ref *cxl_rr = NULL, *iter;
> > +	struct cxl_region_params *p = &cxlr->params;
> > +	struct cxl_decoder *cxld = NULL;
> > +	unsigned long index;
> > +	int rc = -EBUSY;
> > +
> > +	lockdep_assert_held_write(&cxl_region_rwsem);
> > +
> > +	xa_for_each(&port->regions, index, iter) {
> > +		struct cxl_region_params *ip = &iter->region->params;
> > +
> > +		if (iter->region == cxlr)
> > +			cxl_rr = iter;
> > +		if (ip->res->start > p->res->start) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: HPA order violation %s:%pr vs %pr\n",
> > +				dev_name(&port->dev),
> > +				dev_name(&iter->region->dev), ip->res, p->res);
> > +			return -EBUSY;
> > +		}
> > +	}
> > +
> > +	if (cxl_rr) {
> > +		struct cxl_ep *ep_iter;
> > +		int found = 0;
> > +
> > +		cxld = cxl_rr->decoder;
> > +		xa_for_each(&cxl_rr->endpoints, index, ep_iter) {
> > +			if (ep_iter == ep)
> > +				continue;
> > +			if (ep_iter->next == ep->next) {
> > +				found++;
> > +				break;
> > +			}
> > +		}
> > +
> > +		/*
> > +		 * If this is a new target or if this port is direct connected
> > +		 * to this endpoint then add to the target count.
> > +		 */
> > +		if (!found || !ep->next)
> > +			cxl_rr->nr_targets++;
> > +	} else {
> > +		cxl_rr = alloc_region_ref(port, cxlr);
> > +		if (!cxl_rr) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: failed to allocate region reference\n",
> > +				dev_name(&port->dev));
> > +			return -ENOMEM;
> > +		}
> > +		rc = cxl_rr_add(cxl_rr);
> > +		if (rc) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: failed to track region reference\n",
> > +				dev_name(&port->dev));
> > +			kfree(cxl_rr);
> > +			return rc;
> > +		}
> > +	}
> > +
> > +	if (!cxld) {
> > +		if (port == cxled_to_port(cxled))
> > +			cxld = &cxled->cxld;
> > +		else
> > +			cxld = cxl_region_find_decoder(port, cxlr);
> > +		if (!cxld) {
> > +			dev_dbg(&cxlr->dev, "%s: no decoder available\n",
> > +				dev_name(&port->dev));
> > +			goto out_erase;
> > +		}
> > +
> > +		if (cxld->region) {
> > +			dev_dbg(&cxlr->dev, "%s: %s already attached to %s\n",
> > +				dev_name(&port->dev), dev_name(&cxld->dev),
> > +				dev_name(&cxld->region->dev));
> > +			rc = -EBUSY;
> > +			goto out_erase;
> > +		}
> > +
> > +		cxl_rr->decoder = cxld;
> > +	}
> > +
> > +	rc = cxl_rr_ep_add(cxl_rr, cxled);
> > +	if (rc) {
> > +		dev_dbg(&cxlr->dev,
> > +			"%s: failed to track endpoint %s:%s reference\n",
> > +			dev_name(&port->dev), dev_name(&cxlmd->dev),
> > +			dev_name(&cxld->dev));
> > +		goto out_erase;
> > +	}
> > +
> > +	return 0;
> > +out_erase:
> > +	if (cxl_rr->nr_eps == 0)
> > +		free_region_ref(cxl_rr);
> > +	return rc;
> > +}
> > +
> > +static struct cxl_region_ref *cxl_rr_load(struct cxl_port *port,
> > +					  struct cxl_region *cxlr)
> > +{
> > +	return xa_load(&port->regions, (unsigned long)cxlr);
> > +}
> > +
> > +static void cxl_port_detach_region(struct cxl_port *port,
> > +				   struct cxl_region *cxlr,
> > +				   struct cxl_endpoint_decoder *cxled)
> > +{
> > +	struct cxl_region_ref *cxl_rr;
> > +	struct cxl_ep *ep;
> > +
> > +	lockdep_assert_held_write(&cxl_region_rwsem);
> > +
> > +	cxl_rr = cxl_rr_load(port, cxlr);
> > +	if (!cxl_rr)
> > +		return;
> > +
> > +	ep = xa_erase(&cxl_rr->endpoints, (unsigned long)cxled);
> > +	if (ep) {
> > +		struct cxl_ep *ep_iter;
> > +		unsigned long index;
> > +		int found = 0;
> > +
> > +		cxl_rr->nr_eps--;
> > +		xa_for_each(&cxl_rr->endpoints, index, ep_iter) {
> > +			if (ep_iter->next == ep->next) {
> > +				found++;
> > +				break;
> > +			}
> > +		}
> > +		if (!found)
> > +			cxl_rr->nr_targets--;
> > +	}
> > +
> > +	if (cxl_rr->nr_eps == 0)
> > +		free_region_ref(cxl_rr);
> > +}
> > +
> >  /*
> >   * - Check that the given endpoint is attached to a host-bridge identified
> >   *   in the root interleave.
> > @@ -435,14 +683,28 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
> >  static int cxl_region_attach(struct cxl_region *cxlr,
> >  			     struct cxl_endpoint_decoder *cxled, int pos)
> >  {
> > +	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> > +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> > +	struct cxl_port *ep_port, *root_port, *iter;
> >  	struct cxl_region_params *p = &cxlr->params;
> > +	struct cxl_dport *dport;
> > +	int i, rc = -ENXIO;
> >  
> >  	if (cxled->mode == CXL_DECODER_DEAD) {
> >  		dev_dbg(&cxlr->dev, "%s dead\n", dev_name(&cxled->cxld.dev));
> >  		return -ENODEV;
> >  	}
> >  
> > -	if (pos >= p->interleave_ways) {
> > +	/* all full of members, or interleave config not established? */
> > +	if (p->state > CXL_CONFIG_INTERLEAVE_ACTIVE) {
> > +		dev_dbg(&cxlr->dev, "region already active\n");
> > +		return -EBUSY;
> > +	} else if (p->state < CXL_CONFIG_INTERLEAVE_ACTIVE) {
> > +		dev_dbg(&cxlr->dev, "interleave config missing\n");
> > +		return -ENXIO;
> > +	}
> > +
> > +	if (pos < 0 || pos >= p->interleave_ways) {
> >  		dev_dbg(&cxlr->dev, "position %d out of range %d\n", pos,
> >  			p->interleave_ways);
> >  		return -ENXIO;
> > @@ -461,15 +723,83 @@ static int cxl_region_attach(struct cxl_region *cxlr,
> >  		return -EBUSY;
> >  	}
> >  
> > +	for (i = 0; i < p->interleave_ways; i++) {
> > +		struct cxl_endpoint_decoder *cxled_target;
> > +		struct cxl_memdev *cxlmd_target;
> > +
> > +		cxled_target = p->targets[pos];
> > +		if (!cxled_target)
> > +			continue;
> > +
> > +		cxlmd_target = cxled_to_memdev(cxled_target);
> > +		if (cxlmd_target == cxlmd) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s already specified at position %d via: %s\n",
> > +				dev_name(&cxlmd->dev), pos,
> > +				dev_name(&cxled_target->cxld.dev));
> > +			return -EBUSY;
> > +		}
> > +	}
> > +
> > +	ep_port = cxled_to_port(cxled);
> > +	root_port = cxlrd_to_port(cxlrd);
> > +	dport = cxl_dport_load(root_port, ep_port->host_bridge);
> > +	if (!dport) {
> > +		dev_dbg(&cxlr->dev, "%s:%s invalid target for %s\n",
> > +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> > +			dev_name(cxlr->dev.parent));
> > +		return -ENXIO;
> > +	}
> > +
> > +	if (cxlrd->calc_hb(cxlrd, pos) != dport) {
> > +		dev_dbg(&cxlr->dev, "%s:%s invalid target position for %s\n",
> > +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> > +			dev_name(&cxlrd->cxlsd.cxld.dev));
> > +		return -ENXIO;
> > +	}
> > +
> > +	if (cxled->cxld.target_type != cxlr->type) {
> > +		dev_dbg(&cxlr->dev, "%s:%s type mismatch: %d vs %d\n",
> > +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> > +			cxled->cxld.target_type, cxlr->type);
> > +		return -ENXIO;
> > +	}
> > +
> > +	if (resource_size(cxled->dpa_res) * p->interleave_ways !=
> 
> At this point cxled->dpa_res is NULL.

Will take a look, thanks.

Jonathan Cameron wrote:
> On Thu, 23 Jun 2022 21:19:44 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
> 
> > CXL regions (interleave sets) are made up of a set of memory devices
> > where each device maps a portion of the interleave with one of its
> > decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
> > As endpoint decoders are identified by a provisioning tool they can be
> > added to a region provided the region interleave properties are set
> > (way, granularity, HPA) and DPA has been assigned to the decoder.
> > 
> > The attach event triggers several validation checks, for example:
> > - is the DPA sized appropriately for the region
> > - is the decoder reachable via the host-bridges identified by the
> >   region's root decoder
> > - is the device already active in a different region position slot
> > - are there already regions with a higher HPA active on a given port
> >   (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)
> > 
> > ...and the attach event affords an opportunity to collect data and
> > resources relevant to later programming the target lists in switch
> > decoders, for example:
> > - allocate a decoder at each cxl_port in the decode chain
> > - for a given switch port, how many the region's endpoints are hosted
> >   through the port
> > - how many unique targets (next hops) does a port need to map to reach
> >   those endpoints
> > 
> > The act of reconciling this information and deploying it to the decoder
> > configuration is saved for a follow-on patch.
> Hi Dam,
> n
> Only managed to grab a few mins today to debug that crash.. So I know
> the immediate cause but not yet why we got to that state.
> 
> Test case (happened to be one I had open) is 2x HB, 2x RP on each,
> direct connected type 3s on all ports.
> 
> Manual test script is:
> 
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/core/cxl_core.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_acpi.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_port.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pci.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_mem.ko
> insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pmem.ko
> 
> cd /sys/bus/cxl/devices/decoder0.0/
> cat create_pmem_region
> echo region0 > create_pmem_region
> 
> cd region0/
> echo 4 > interleave_ways
> echo $((256 << 22)) > size
> echo 6a6b9b22-e0d4-11ec-9d64-0242ac120002 > uuid
> ls -lh /sys/bus/cxl/devices/endpoint?/upo*
> 
> # Then figure out the order hopefully write the correct targets 
> echo decoder5.0 > target0

Oh, something simple in the end. Just need to check that DPA is assigned
before region attach. I folded the following into patch 40:

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 0b5acabcc541..d52c97e941fe 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -765,10 +765,17 @@ static int cxl_region_attach(struct cxl_region *cxlr,
                return -ENXIO;
        }
 
+       if (!cxled->dpa_res) {
+               dev_dbg(&cxlr->dev, "%s:%s: missing DPA allocation.\n",
+                       dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev));
+               return -ENXIO;
+       }
+
        if (resource_size(cxled->dpa_res) * p->interleave_ways !=
            resource_size(p->res)) {
                dev_dbg(&cxlr->dev,
-                       "decoder-size-%#llx * ways-%d != region-size-%#llx\n",
+                       "%s:%s: decoder-size-%#llx * ways-%d != region-size-%#llx\n",
+                       dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
                        (u64)resource_size(cxled->dpa_res), p->interleave_ways,
                        (u64)resource_size(p->res));
                return -EINVAL;

Dan Williams wrote:
> Jonathan Cameron wrote:
> > On Thu, 23 Jun 2022 21:19:44 -0700
> > Dan Williams <dan.j.williams@intel.com> wrote:
> > 
> > > CXL regions (interleave sets) are made up of a set of memory devices
> > > where each device maps a portion of the interleave with one of its
> > > decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
> > > As endpoint decoders are identified by a provisioning tool they can be
> > > added to a region provided the region interleave properties are set
> > > (way, granularity, HPA) and DPA has been assigned to the decoder.
> > > 
> > > The attach event triggers several validation checks, for example:
> > > - is the DPA sized appropriately for the region
> > > - is the decoder reachable via the host-bridges identified by the
> > >   region's root decoder
> > > - is the device already active in a different region position slot
> > > - are there already regions with a higher HPA active on a given port
> > >   (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)
> > > 
> > > ...and the attach event affords an opportunity to collect data and
> > > resources relevant to later programming the target lists in switch
> > > decoders, for example:
> > > - allocate a decoder at each cxl_port in the decode chain
> > > - for a given switch port, how many the region's endpoints are hosted
> > >   through the port
> > > - how many unique targets (next hops) does a port need to map to reach
> > >   those endpoints
> > > 
> > > The act of reconciling this information and deploying it to the decoder
> > > configuration is saved for a follow-on patch.
> > Hi Dam,
> > n
> > Only managed to grab a few mins today to debug that crash.. So I know
> > the immediate cause but not yet why we got to that state.
> > 
> > Test case (happened to be one I had open) is 2x HB, 2x RP on each,
> > direct connected type 3s on all ports.
> > 
> > Manual test script is:
> > 
> > insmod modules/5.19.0-rc3+/kernel/drivers/cxl/core/cxl_core.ko
> > insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_acpi.ko
> > insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_port.ko
> > insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pci.ko
> > insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_mem.ko
> > insmod modules/5.19.0-rc3+/kernel/drivers/cxl/cxl_pmem.ko
> > 
> > cd /sys/bus/cxl/devices/decoder0.0/
> > cat create_pmem_region
> > echo region0 > create_pmem_region
> > 
> > cd region0/
> > echo 4 > interleave_ways
> > echo $((256 << 22)) > size
> > echo 6a6b9b22-e0d4-11ec-9d64-0242ac120002 > uuid
> > ls -lh /sys/bus/cxl/devices/endpoint?/upo*
> > 
> > # Then figure out the order hopefully write the correct targets 
> > echo decoder5.0 > target0
> 
> Oh, something simple in the end. Just need to check that DPA is assigned
> before region attach. I folded the following into patch 40:

BTW, as I'm finding these things I'm force pushing the preview branch
with the updates, so this one is fixed as of current HEAD at:

1985cf588505 cxl/region: Introduce cxl_pmem_region objects

On Thu, 23 Jun 2022 21:19:44 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> CXL regions (interleave sets) are made up of a set of memory devices
> where each device maps a portion of the interleave with one of its
> decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
> As endpoint decoders are identified by a provisioning tool they can be
> added to a region provided the region interleave properties are set
> (way, granularity, HPA) and DPA has been assigned to the decoder.
> 
> The attach event triggers several validation checks, for example:
> - is the DPA sized appropriately for the region
> - is the decoder reachable via the host-bridges identified by the
>   region's root decoder
> - is the device already active in a different region position slot
> - are there already regions with a higher HPA active on a given port
>   (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)
> 
> ...and the attach event affords an opportunity to collect data and
> resources relevant to later programming the target lists in switch
> decoders, for example:
> - allocate a decoder at each cxl_port in the decode chain
> - for a given switch port, how many the region's endpoints are hosted
>   through the port
> - how many unique targets (next hops) does a port need to map to reach
>   those endpoints
> 
> The act of reconciling this information and deploying it to the decoder
> configuration is saved for a follow-on patch.
> 
> Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
> Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/cxl/core/core.h   |   7 +
>  drivers/cxl/core/port.c   |  10 +-
>  drivers/cxl/core/region.c | 338 +++++++++++++++++++++++++++++++++++++-
>  drivers/cxl/cxl.h         |  20 +++
>  drivers/cxl/cxlmem.h      |   5 +
>  5 files changed, 372 insertions(+), 8 deletions(-)
> 


> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 4830365f3857..65bf84abad57 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -428,6 +428,254 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
>  	return rc;
>  }
>  

> +
> +static struct cxl_region_ref *alloc_region_ref(struct cxl_port *port,
> +					       struct cxl_region *cxlr)
> +{
> +	struct cxl_region_ref *cxl_rr;
> +
> +	cxl_rr = kzalloc(sizeof(*cxl_rr), GFP_KERNEL);
> +	if (!cxl_rr)
> +		return NULL;
> +	cxl_rr->port = port;
> +	cxl_rr->region = cxlr;
> +	xa_init(&cxl_rr->endpoints);
> +	return cxl_rr;
> +}
> +
> +static void free_region_ref(struct cxl_region_ref *cxl_rr)
> +{
> +	struct cxl_port *port = cxl_rr->port;
> +	struct cxl_region *cxlr = cxl_rr->region;
> +	struct cxl_decoder *cxld = cxl_rr->decoder;
> +
> +	dev_WARN_ONCE(&cxlr->dev, cxld->region != cxlr, "region mismatch\n");
> +	if (cxld->region == cxlr) {
> +		cxld->region = NULL;
> +		put_device(&cxlr->dev);
> +	}
> +
> +	xa_erase(&port->regions, (unsigned long)cxlr);

Why do we have things in a free_ function that aren't simply removing things
created in the alloc()?  I'd kind of expect this to be in a cxl_rr_del() or similar.

> +	xa_destroy(&cxl_rr->endpoints);
> +	kfree(cxl_rr);
> +}
> +
> +static int cxl_rr_add(struct cxl_region_ref *cxl_rr)
> +{
> +	struct cxl_port *port = cxl_rr->port;
> +	struct cxl_region *cxlr = cxl_rr->region;
> +
> +	return xa_insert(&port->regions, (unsigned long)cxlr, cxl_rr,
> +			 GFP_KERNEL);
> +}
> +
> +static int cxl_rr_ep_add(struct cxl_region_ref *cxl_rr,
> +			 struct cxl_endpoint_decoder *cxled)
> +{
> +	int rc;
> +	struct cxl_port *port = cxl_rr->port;
> +	struct cxl_region *cxlr = cxl_rr->region;
> +	struct cxl_decoder *cxld = cxl_rr->decoder;
> +	struct cxl_ep *ep = cxl_ep_load(port, cxled_to_memdev(cxled));
> +
> +	rc = xa_insert(&cxl_rr->endpoints, (unsigned long)cxled, ep,
> +			 GFP_KERNEL);
> +	if (rc)
> +		return rc;
> +	cxl_rr->nr_eps++;
> +
> +	if (!cxld->region) {
> +		cxld->region = cxlr;
> +		get_device(&cxlr->dev);
> +	}
> +
> +	return 0;
> +}
> +
> +static int cxl_port_attach_region(struct cxl_port *port,
> +				  struct cxl_region *cxlr,
> +				  struct cxl_endpoint_decoder *cxled, int pos)
> +{
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_ep *ep = cxl_ep_load(port, cxlmd);
> +	struct cxl_region_ref *cxl_rr = NULL, *iter;
> +	struct cxl_region_params *p = &cxlr->params;
> +	struct cxl_decoder *cxld = NULL;
> +	unsigned long index;
> +	int rc = -EBUSY;
> +
> +	lockdep_assert_held_write(&cxl_region_rwsem);

This function is complex enough that maybe it would benefit from
some saying what each part is doing.

> +
> +	xa_for_each(&port->regions, index, iter) {
> +		struct cxl_region_params *ip = &iter->region->params;
> +
> +		if (iter->region == cxlr)
> +			cxl_rr = iter;
> +		if (ip->res->start > p->res->start) {
> +			dev_dbg(&cxlr->dev,
> +				"%s: HPA order violation %s:%pr vs %pr\n",
> +				dev_name(&port->dev),
> +				dev_name(&iter->region->dev), ip->res, p->res);
> +			return -EBUSY;
> +		}
> +	}
> +
> +	if (cxl_rr) {
> +		struct cxl_ep *ep_iter;
> +		int found = 0;
> +
> +		cxld = cxl_rr->decoder;
> +		xa_for_each(&cxl_rr->endpoints, index, ep_iter) {
> +			if (ep_iter == ep)
> +				continue;
> +			if (ep_iter->next == ep->next) {
> +				found++;
> +				break;
> +			}
> +		}
> +
> +		/*
> +		 * If this is a new target or if this port is direct connected
> +		 * to this endpoint then add to the target count.
> +		 */
> +		if (!found || !ep->next)
> +			cxl_rr->nr_targets++;
> +	} else {
> +		cxl_rr = alloc_region_ref(port, cxlr);
> +		if (!cxl_rr) {
> +			dev_dbg(&cxlr->dev,
> +				"%s: failed to allocate region reference\n",
> +				dev_name(&port->dev));
> +			return -ENOMEM;
> +		}
> +		rc = cxl_rr_add(cxl_rr);
> +		if (rc) {
> +			dev_dbg(&cxlr->dev,
> +				"%s: failed to track region reference\n",
> +				dev_name(&port->dev));
> +			kfree(cxl_rr);
> +			return rc;
> +		}
> +	}
> +
> +	if (!cxld) {
> +		if (port == cxled_to_port(cxled))
> +			cxld = &cxled->cxld;
> +		else
> +			cxld = cxl_region_find_decoder(port, cxlr);
> +		if (!cxld) {
> +			dev_dbg(&cxlr->dev, "%s: no decoder available\n",
> +				dev_name(&port->dev));
> +			goto out_erase;
> +		}
> +
> +		if (cxld->region) {
> +			dev_dbg(&cxlr->dev, "%s: %s already attached to %s\n",
> +				dev_name(&port->dev), dev_name(&cxld->dev),
> +				dev_name(&cxld->region->dev));
> +			rc = -EBUSY;
> +			goto out_erase;
> +		}
> +
> +		cxl_rr->decoder = cxld;
> +	}
> +
> +	rc = cxl_rr_ep_add(cxl_rr, cxled);
> +	if (rc) {
> +		dev_dbg(&cxlr->dev,
> +			"%s: failed to track endpoint %s:%s reference\n",
> +			dev_name(&port->dev), dev_name(&cxlmd->dev),
> +			dev_name(&cxld->dev));
> +		goto out_erase;
> +	}
> +
> +	return 0;
> +out_erase:
> +	if (cxl_rr->nr_eps == 0)
> +		free_region_ref(cxl_rr);
> +	return rc;
> +}
> +

>  
>  static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  {
> +	struct cxl_port *iter, *ep_port = cxled_to_port(cxled);
>  	struct cxl_region *cxlr = cxled->cxld.region;
>  	struct cxl_region_params *p;
>  
> @@ -481,6 +811,10 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  	p = &cxlr->params;
>  	get_device(&cxlr->dev);
>  
> +	for (iter = ep_port; !is_cxl_root(iter);
> +	     iter = to_cxl_port(iter->dev.parent))
> +		cxl_port_detach_region(iter, cxlr, cxled);
> +
>  	if (cxled->pos < 0 || cxled->pos >= p->interleave_ways ||
>  	    p->targets[cxled->pos] != cxled) {
>  		struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> @@ -491,6 +825,8 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  		goto out;
>  	}
>  
> +	if (p->state == CXL_CONFIG_ACTIVE)

I 'think' the state is either CXL_CONFIG_ACTIVE or CXL_CONFIG_INTERLEAVE_ACTIVE,
so you could set this unconditionally.  A comment here on permissible
states would be useful for future reference.

> +		p->state = CXL_CONFIG_INTERLEAVE_ACTIVE;
>  	p->targets[cxled->pos] = NULL;
>  	p->nr_targets--;

Jonathan Cameron wrote:
> On Thu, 23 Jun 2022 21:19:44 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
> 
> > CXL regions (interleave sets) are made up of a set of memory devices
> > where each device maps a portion of the interleave with one of its
> > decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
> > As endpoint decoders are identified by a provisioning tool they can be
> > added to a region provided the region interleave properties are set
> > (way, granularity, HPA) and DPA has been assigned to the decoder.
> > 
> > The attach event triggers several validation checks, for example:
> > - is the DPA sized appropriately for the region
> > - is the decoder reachable via the host-bridges identified by the
> >   region's root decoder
> > - is the device already active in a different region position slot
> > - are there already regions with a higher HPA active on a given port
> >   (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)
> > 
> > ...and the attach event affords an opportunity to collect data and
> > resources relevant to later programming the target lists in switch
> > decoders, for example:
> > - allocate a decoder at each cxl_port in the decode chain
> > - for a given switch port, how many the region's endpoints are hosted
> >   through the port
> > - how many unique targets (next hops) does a port need to map to reach
> >   those endpoints
> > 
> > The act of reconciling this information and deploying it to the decoder
> > configuration is saved for a follow-on patch.
> > 
> > Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
> > Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > ---
> >  drivers/cxl/core/core.h   |   7 +
> >  drivers/cxl/core/port.c   |  10 +-
> >  drivers/cxl/core/region.c | 338 +++++++++++++++++++++++++++++++++++++-
> >  drivers/cxl/cxl.h         |  20 +++
> >  drivers/cxl/cxlmem.h      |   5 +
> >  5 files changed, 372 insertions(+), 8 deletions(-)
> > 
> 
> 
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index 4830365f3857..65bf84abad57 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -428,6 +428,254 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
> >  	return rc;
> >  }
> >  
> 
> > +
> > +static struct cxl_region_ref *alloc_region_ref(struct cxl_port *port,
> > +					       struct cxl_region *cxlr)
> > +{
> > +	struct cxl_region_ref *cxl_rr;
> > +
> > +	cxl_rr = kzalloc(sizeof(*cxl_rr), GFP_KERNEL);
> > +	if (!cxl_rr)
> > +		return NULL;
> > +	cxl_rr->port = port;
> > +	cxl_rr->region = cxlr;
> > +	xa_init(&cxl_rr->endpoints);
> > +	return cxl_rr;
> > +}
> > +
> > +static void free_region_ref(struct cxl_region_ref *cxl_rr)
> > +{
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +	struct cxl_decoder *cxld = cxl_rr->decoder;
> > +
> > +	dev_WARN_ONCE(&cxlr->dev, cxld->region != cxlr, "region mismatch\n");
> > +	if (cxld->region == cxlr) {
> > +		cxld->region = NULL;
> > +		put_device(&cxlr->dev);
> > +	}
> > +
> > +	xa_erase(&port->regions, (unsigned long)cxlr);
> 
> Why do we have things in a free_ function that aren't simply removing things
> created in the alloc()?  I'd kind of expect this to be in a cxl_rr_del() or similar.

Fixed it the other way by just open-coding cxl_rr_add() into
alloc_region_ref(). There was no good reason to have them as separate
steps.

> 
> > +	xa_destroy(&cxl_rr->endpoints);
> > +	kfree(cxl_rr);
> > +}
> > +
> > +static int cxl_rr_add(struct cxl_region_ref *cxl_rr)
> > +{
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +
> > +	return xa_insert(&port->regions, (unsigned long)cxlr, cxl_rr,
> > +			 GFP_KERNEL);
> > +}
> > +
> > +static int cxl_rr_ep_add(struct cxl_region_ref *cxl_rr,
> > +			 struct cxl_endpoint_decoder *cxled)
> > +{
> > +	int rc;
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +	struct cxl_decoder *cxld = cxl_rr->decoder;
> > +	struct cxl_ep *ep = cxl_ep_load(port, cxled_to_memdev(cxled));
> > +
> > +	rc = xa_insert(&cxl_rr->endpoints, (unsigned long)cxled, ep,
> > +			 GFP_KERNEL);
> > +	if (rc)
> > +		return rc;
> > +	cxl_rr->nr_eps++;
> > +
> > +	if (!cxld->region) {
> > +		cxld->region = cxlr;
> > +		get_device(&cxlr->dev);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int cxl_port_attach_region(struct cxl_port *port,
> > +				  struct cxl_region *cxlr,
> > +				  struct cxl_endpoint_decoder *cxled, int pos)
> > +{
> > +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> > +	struct cxl_ep *ep = cxl_ep_load(port, cxlmd);
> > +	struct cxl_region_ref *cxl_rr = NULL, *iter;
> > +	struct cxl_region_params *p = &cxlr->params;
> > +	struct cxl_decoder *cxld = NULL;
> > +	unsigned long index;
> > +	int rc = -EBUSY;
> > +
> > +	lockdep_assert_held_write(&cxl_region_rwsem);
> 
> This function is complex enough that maybe it would benefit from
> some saying what each part is doing.

...added a kdoc block:

/**
 * cxl_port_attach_region() - track a region's interest in a port by endpoint
 * @port: port to add a new region reference 'struct cxl_region_ref'
 * @cxlr: region to attach to @port
 * @cxled: endpoint decoder used to create or further pin a region reference
 * @pos: interleave position of @cxled in @cxlr
 *
 * The attach event is an opportunity to validate CXL decode setup
 * constraints and record metadata needed for programming HDM decoders,
 * in particular decoder target lists.
 *
 * The steps are:
 * - validate that there are no other regions with a higher HPA already
 *   associated with @port
 * - establish a region reference if one is not already present
 *   - additionally allocate a decoder instance that will host @cxlr on
 *     @port
 * - pin the region reference by the endpoint
 * - account for how many entries in @port's target list are needed to
 *   cover all of the added endpoints.
 */

> 
> > +
> > +	xa_for_each(&port->regions, index, iter) {
> > +		struct cxl_region_params *ip = &iter->region->params;
> > +
> > +		if (iter->region == cxlr)
> > +			cxl_rr = iter;
> > +		if (ip->res->start > p->res->start) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: HPA order violation %s:%pr vs %pr\n",
> > +				dev_name(&port->dev),
> > +				dev_name(&iter->region->dev), ip->res, p->res);
> > +			return -EBUSY;
> > +		}
> > +	}
> > +
> > +	if (cxl_rr) {
> > +		struct cxl_ep *ep_iter;
> > +		int found = 0;
> > +
> > +		cxld = cxl_rr->decoder;
> > +		xa_for_each(&cxl_rr->endpoints, index, ep_iter) {
> > +			if (ep_iter == ep)
> > +				continue;
> > +			if (ep_iter->next == ep->next) {
> > +				found++;
> > +				break;
> > +			}
> > +		}
> > +
> > +		/*
> > +		 * If this is a new target or if this port is direct connected
> > +		 * to this endpoint then add to the target count.
> > +		 */
> > +		if (!found || !ep->next)
> > +			cxl_rr->nr_targets++;
> > +	} else {
> > +		cxl_rr = alloc_region_ref(port, cxlr);
> > +		if (!cxl_rr) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: failed to allocate region reference\n",
> > +				dev_name(&port->dev));
> > +			return -ENOMEM;
> > +		}
> > +		rc = cxl_rr_add(cxl_rr);
> > +		if (rc) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: failed to track region reference\n",
> > +				dev_name(&port->dev));
> > +			kfree(cxl_rr);
> > +			return rc;
> > +		}
> > +	}
> > +
> > +	if (!cxld) {
> > +		if (port == cxled_to_port(cxled))
> > +			cxld = &cxled->cxld;
> > +		else
> > +			cxld = cxl_region_find_decoder(port, cxlr);
> > +		if (!cxld) {
> > +			dev_dbg(&cxlr->dev, "%s: no decoder available\n",
> > +				dev_name(&port->dev));
> > +			goto out_erase;
> > +		}
> > +
> > +		if (cxld->region) {
> > +			dev_dbg(&cxlr->dev, "%s: %s already attached to %s\n",
> > +				dev_name(&port->dev), dev_name(&cxld->dev),
> > +				dev_name(&cxld->region->dev));
> > +			rc = -EBUSY;
> > +			goto out_erase;
> > +		}
> > +
> > +		cxl_rr->decoder = cxld;
> > +	}
> > +
> > +	rc = cxl_rr_ep_add(cxl_rr, cxled);
> > +	if (rc) {
> > +		dev_dbg(&cxlr->dev,
> > +			"%s: failed to track endpoint %s:%s reference\n",
> > +			dev_name(&port->dev), dev_name(&cxlmd->dev),
> > +			dev_name(&cxld->dev));
> > +		goto out_erase;
> > +	}
> > +
> > +	return 0;
> > +out_erase:
> > +	if (cxl_rr->nr_eps == 0)
> > +		free_region_ref(cxl_rr);
> > +	return rc;
> > +}
> > +
> 
> >  
> >  static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
> >  {
> > +	struct cxl_port *iter, *ep_port = cxled_to_port(cxled);
> >  	struct cxl_region *cxlr = cxled->cxld.region;
> >  	struct cxl_region_params *p;
> >  
> > @@ -481,6 +811,10 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
> >  	p = &cxlr->params;
> >  	get_device(&cxlr->dev);
> >  
> > +	for (iter = ep_port; !is_cxl_root(iter);
> > +	     iter = to_cxl_port(iter->dev.parent))
> > +		cxl_port_detach_region(iter, cxlr, cxled);
> > +
> >  	if (cxled->pos < 0 || cxled->pos >= p->interleave_ways ||
> >  	    p->targets[cxled->pos] != cxled) {
> >  		struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> > @@ -491,6 +825,8 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
> >  		goto out;
> >  	}
> >  
> > +	if (p->state == CXL_CONFIG_ACTIVE)
> 
> I 'think' the state is either CXL_CONFIG_ACTIVE or CXL_CONFIG_INTERLEAVE_ACTIVE,
> so you could set this unconditionally.  A comment here on permissible
> states would be useful for future reference.

cxl_region_detach() should not care if the region state is idle. Not
that it will happen in the current code, but the only expectation is
that if the region is active and a endpoint departs it must be
downgraded in config state. CXL_CONFIG_IDLE is permissible, although not
expected. I do not think a comment is needed if the "if (p->state ==
CXL_CONFIG_ACTIVE)" check stays.

> 
> > +		p->state = CXL_CONFIG_INTERLEAVE_ACTIVE;
> >  	p->targets[cxled->pos] = NULL;
> >  	p->nr_targets--;
> 
>