[2/3] powerpc/powernv: DMA operations for discontiguous allocation

DMA pseudo-bypass is a new set of DMA operations that solve some issues for
devices that want to address more than 32 bits but can't address the 59
bits required to enable direct DMA.

The previous implementation for POWER8/PHB3 worked around this by
configuring a bypass from the default 32-bit address space into 64-bit
address space.  This approach does not work for POWER9/PHB4 because
regions of memory are discontiguous and many devices will be unable to
address memory beyond the first node.

Instead, implement a new set of DMA operations that allocate TCEs as DMA
mappings are requested so that all memory is addressable even when a
one-to-one mapping between real addresses and DMA addresses isn't
possible.  These TCEs are the maximum size available on the platform,
which is 256M on PHB3 and 1G on PHB4.

Devices can now map any region of memory up to the maximum amount they can
address according to the DMA mask set, in chunks of the largest available
TCE size.

This implementation replaces the need for the existing PHB3 solution and
should be compatible with future PHB versions.

It is, however, rather naive.  There is no unmapping, and as a result
devices can eventually run out of space if they address their entire
DMA mask worth of TCEs.  An implementation with unmap() will come in
future (and requires a much more complex implementation), but this is a
good start due to the drastic performance improvement.

Signed-off-by: Russell Currey <ruscur@russell.cc>
---
 arch/powerpc/include/asm/dma-mapping.h    |   1 +
 arch/powerpc/platforms/powernv/Makefile   |   2 +-
 arch/powerpc/platforms/powernv/pci-dma.c  | 243 ++++++++++++++++++++++
 arch/powerpc/platforms/powernv/pci-ioda.c |  82 +++-----
 arch/powerpc/platforms/powernv/pci.h      |   7 +
 5 files changed, 281 insertions(+), 54 deletions(-)
 create mode 100644 arch/powerpc/platforms/powernv/pci-dma.c

On Fri, 2018-06-29 at 17:34 +1000, Russell Currey wrote:
> DMA pseudo-bypass is a new set of DMA operations that solve some issues for
> devices that want to address more than 32 bits but can't address the 59
> bits required to enable direct DMA.

One thing you may need to add (I didn't see it with a cursory glance
but maybe it's there) is some form of handling of allocations or
mapping requests that span a TCE boundary.

For allocations, since they are page orders, that means you only have
to check if they are bigger than a TCE page.

For mappings, you need to check individual sglist entries.

At this stage, if you hit that all you can do is fail, with maybe a
rate limited printk. But it's better than whatever corruption or
misbehaviour will happen if you don't catch them. I don't expect this
to happen much if at all with 1G pages, as most "sg" mappings are
probably be in unit of pages, but I still want to catch if it does
happen.

> The previous implementation for POWER8/PHB3 worked around this by
> configuring a bypass from the default 32-bit address space into 64-bit
> address space.  This approach does not work for POWER9/PHB4 because
> regions of memory are discontiguous and many devices will be unable to
> address memory beyond the first node.
> 
> Instead, implement a new set of DMA operations that allocate TCEs as DMA
> mappings are requested so that all memory is addressable even when a
> one-to-one mapping between real addresses and DMA addresses isn't
> possible.  These TCEs are the maximum size available on the platform,
> which is 256M on PHB3 and 1G on PHB4.
> 
> Devices can now map any region of memory up to the maximum amount they can
> address according to the DMA mask set, in chunks of the largest available
> TCE size.
> 
> This implementation replaces the need for the existing PHB3 solution and
> should be compatible with future PHB versions.
> 
> It is, however, rather naive.  There is no unmapping, and as a result
> devices can eventually run out of space if they address their entire
> DMA mask worth of TCEs.  An implementation with unmap() will come in
> future (and requires a much more complex implementation), but this is a
> good start due to the drastic performance improvement.
> 
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> ---
>  arch/powerpc/include/asm/dma-mapping.h    |   1 +
>  arch/powerpc/platforms/powernv/Makefile   |   2 +-
>  arch/powerpc/platforms/powernv/pci-dma.c  | 243 ++++++++++++++++++++++
>  arch/powerpc/platforms/powernv/pci-ioda.c |  82 +++-----
>  arch/powerpc/platforms/powernv/pci.h      |   7 +
>  5 files changed, 281 insertions(+), 54 deletions(-)
>  create mode 100644 arch/powerpc/platforms/powernv/pci-dma.c
> 
> diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h
> index 8fa394520af6..354f435160f3 100644
> --- a/arch/powerpc/include/asm/dma-mapping.h
> +++ b/arch/powerpc/include/asm/dma-mapping.h
> @@ -74,6 +74,7 @@ static inline unsigned long device_to_mask(struct device *dev)
>  extern struct dma_map_ops dma_iommu_ops;
>  #endif
>  extern const struct dma_map_ops dma_nommu_ops;
> +extern const struct dma_map_ops dma_pseudo_bypass_ops;
>  
>  static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
>  {
> diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
> index 703a350a7f4e..2467bdab3c13 100644
> --- a/arch/powerpc/platforms/powernv/Makefile
> +++ b/arch/powerpc/platforms/powernv/Makefile
> @@ -6,7 +6,7 @@ obj-y			+= opal-msglog.o opal-hmi.o opal-power.o opal-irqchip.o
>  obj-y			+= opal-kmsg.o opal-powercap.o opal-psr.o opal-sensor-groups.o
>  
>  obj-$(CONFIG_SMP)	+= smp.o subcore.o subcore-asm.o
> -obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o
> +obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o pci-dma.o
>  obj-$(CONFIG_CXL_BASE)	+= pci-cxl.o
>  obj-$(CONFIG_EEH)	+= eeh-powernv.o
>  obj-$(CONFIG_PPC_SCOM)	+= opal-xscom.o
> diff --git a/arch/powerpc/platforms/powernv/pci-dma.c b/arch/powerpc/platforms/powernv/pci-dma.c
> new file mode 100644
> index 000000000000..79382627c7be
> --- /dev/null
> +++ b/arch/powerpc/platforms/powernv/pci-dma.c
> @@ -0,0 +1,243 @@
> +/*
> + * DMA operations supporting pseudo-bypass for PHB3+
> + *
> + * Author: Russell Currey <ruscur@russell.cc>
> + *
> + * Copyright 2018 IBM Corporation.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the
> + * Free Software Foundation; either version 2 of the License, or (at your
> + * option) any later version.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/memblock.h>
> +#include <linux/device.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/hash.h>
> +
> +#include <asm/pci-bridge.h>
> +#include <asm/ppc-pci.h>
> +#include <asm/pnv-pci.h>
> +#include <asm/tce.h>
> +
> +#include "pci.h"
> +
> +/*
> + * This is a naive implementation that directly operates on TCEs, allocating
> + * on demand.  There is no locking or refcounts since no TCEs are ever removed
> + * and unmap does nothing.
> + */
> +static dma_addr_t dma_pseudo_bypass_get_address(struct device *dev,
> +					    phys_addr_t addr)
> +{
> +	struct pci_dev *pdev = container_of(dev, struct pci_dev, dev);
> +	struct pci_controller *hose = pci_bus_to_host(pdev->bus);
> +	struct pnv_phb *phb = hose->private_data;
> +	struct pnv_ioda_pe *pe;
> +	u64 i, tce, ret, offset;
> +	__be64 entry;
> +
> +	offset = addr & ((1 << phb->ioda.max_tce_order) - 1);
> +
> +	pe = &phb->ioda.pe_array[pci_get_pdn(pdev)->pe_number];
> +
> +	/* look through the tracking table for a free entry */
> +	for (i = 0; i < pe->tce_count; i++) {
> +		/* skip between 2GB and 4GB */
> +		if ((i << phb->ioda.max_tce_order) >= 0x80000000 &&
> +		    (i << phb->ioda.max_tce_order) < 0x100000000)
> +			continue;
> +
> +		tce = be64_to_cpu(pe->tces[i]);
> +
> +		/* if the TCE is already valid (read + write) */
> +		if ((tce & 3) == 3) {
> +			/* check if we're already allocated, if not move on */
> +			if (tce >> phb->ioda.max_tce_order ==
> +			    addr >> phb->ioda.max_tce_order) {
> +				/* wait for the lock bit to clear */
> +				while (be64_to_cpu(pe->tces[i]) & 4)
> +					cpu_relax();
> +
> +				return (i << phb->ioda.max_tce_order) | offset;
> +			}
> +
> +			continue;
> +		}
> +
> +		/*
> +		 * The TCE isn't being used, so let's try and allocate it.
> +		 * Bits 0 and 1 are read/write, and we use bit 2 as a "lock"
> +		 * bit.  This is to prevent any race where the value is set in
> +		 * the TCE table but the invalidate/mb() hasn't finished yet.
> +		 */
> +		entry = cpu_to_be64((addr - offset) | 7);
> +		ret = cmpxchg(&pe->tces[i], tce, entry);
> +		if (ret != tce) {
> +			/* conflict, start looking again just in case */
> +			i--;
> +			continue;
> +		}
> +		pnv_pci_phb3_tce_invalidate(pe, 0, 0, addr - offset, 1);
> +		mb();
> +		/* clear the lock bit now that we know it's active */
> +		ret = cmpxchg(&pe->tces[i], entry, cpu_to_be64((addr - offset) | 3));
> +		if (ret != entry) {
> +			/* conflict, start looking again just in case */
> +			i--;
> +			continue;
> +		}
> +
> +		return (i << phb->ioda.max_tce_order) | offset;
> +	}
> +	/* If we get here, the table must be full, so error out. */
> +	return -1ULL;
> +}
> +
> +/*
> + * For now, don't actually do anything on unmap.
> + */
> +static void dma_pseudo_bypass_unmap_address(struct device *dev, dma_addr_t dma_addr)
> +{
> +}
> +
> +static int dma_pseudo_bypass_dma_supported(struct device *dev, u64 mask)
> +{
> +	/*
> +	 * Normally dma_supported() checks if the mask is capable of addressing
> +	 * all of memory.  Since we map physical memory in chunks that the
> +	 * device can address, the device will be able to address whatever it
> +	 * wants - just not all at once.
> +	 */
> +	return 1;
> +}
> +
> +static void *dma_pseudo_bypass_alloc_coherent(struct device *dev,
> +					  size_t size,
> +					  dma_addr_t *dma_handle,
> +					  gfp_t flag,
> +					  unsigned long attrs)
> +{
> +	void *ret;
> +	struct page *page;
> +	int node = dev_to_node(dev);
> +
> +	/* ignore region specifiers */
> +	flag &= ~(__GFP_HIGHMEM);
> +
> +	page = alloc_pages_node(node, flag, get_order(size));
> +	if (page == NULL)
> +		return NULL;
> +	ret = page_address(page);
> +	memset(ret, 0, size);
> +	*dma_handle = dma_pseudo_bypass_get_address(dev, __pa(ret));
> +
> +	return ret;
> +}
> +
> +static void dma_pseudo_bypass_free_coherent(struct device *dev,
> +					 size_t size,
> +					 void *vaddr,
> +					 dma_addr_t dma_handle,
> +					 unsigned long attrs)
> +{
> +	free_pages((unsigned long)vaddr, get_order(size));
> +}
> +
> +static int dma_pseudo_bypass_mmap_coherent(struct device *dev,
> +				       struct vm_area_struct *vma,
> +				       void *cpu_addr,
> +				       dma_addr_t handle,
> +				       size_t size,
> +				       unsigned long attrs)
> +{
> +	unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
> +
> +	return remap_pfn_range(vma, vma->vm_start,
> +			       pfn + vma->vm_pgoff,
> +			       vma->vm_end - vma->vm_start,
> +			       vma->vm_page_prot);
> +}
> +
> +static inline dma_addr_t dma_pseudo_bypass_map_page(struct device *dev,
> +						struct page *page,
> +						unsigned long offset,
> +						size_t size,
> +						enum dma_data_direction dir,
> +						unsigned long attrs)
> +{
> +	BUG_ON(dir == DMA_NONE);
> +
> +	return dma_pseudo_bypass_get_address(dev, page_to_phys(page) + offset);
> +}
> +
> +static inline void dma_pseudo_bypass_unmap_page(struct device *dev,
> +					 dma_addr_t dma_address,
> +					 size_t size,
> +					 enum dma_data_direction direction,
> +					 unsigned long attrs)
> +{
> +	dma_pseudo_bypass_unmap_address(dev, dma_address);
> +}
> +
> +
> +static int dma_pseudo_bypass_map_sg(struct device *dev, struct scatterlist *sgl,
> +			     int nents, enum dma_data_direction direction,
> +			     unsigned long attrs)
> +{
> +	struct scatterlist *sg;
> +	int i;
> +
> +
> +	for_each_sg(sgl, sg, nents, i) {
> +		sg->dma_address = dma_pseudo_bypass_get_address(dev, sg_phys(sg));
> +		sg->dma_length = sg->length;
> +
> +		__dma_sync_page(sg_page(sg), sg->offset, sg->length, direction);
> +	}
> +
> +	return nents;
> +}
> +
> +static void dma_pseudo_bypass_unmap_sg(struct device *dev, struct scatterlist *sgl,
> +				int nents, enum dma_data_direction direction,
> +				unsigned long attrs)
> +{
> +	struct scatterlist *sg;
> +	int i;
> +
> +	for_each_sg(sgl, sg, nents, i) {
> +		dma_pseudo_bypass_unmap_address(dev, sg->dma_address);
> +	}
> +}
> +
> +static u64 dma_pseudo_bypass_get_required_mask(struct device *dev)
> +{
> +	/*
> +	 * there's no limitation on our end, the driver should just call
> +	 * set_mask() with as many bits as the device can address.
> +	 */
> +	return -1ULL;
> +}
> +
> +static int dma_pseudo_bypass_mapping_error(struct device *dev, dma_addr_t dma_addr)
> +{
> +	return dma_addr == -1ULL;
> +}
> +
> +
> +const struct dma_map_ops dma_pseudo_bypass_ops = {
> +	.alloc				= dma_pseudo_bypass_alloc_coherent,
> +	.free				= dma_pseudo_bypass_free_coherent,
> +	.mmap				= dma_pseudo_bypass_mmap_coherent,
> +	.map_sg				= dma_pseudo_bypass_map_sg,
> +	.unmap_sg			= dma_pseudo_bypass_unmap_sg,
> +	.dma_supported			= dma_pseudo_bypass_dma_supported,
> +	.map_page			= dma_pseudo_bypass_map_page,
> +	.unmap_page			= dma_pseudo_bypass_unmap_page,
> +	.get_required_mask		= dma_pseudo_bypass_get_required_mask,
> +	.mapping_error			= dma_pseudo_bypass_mapping_error,
> +};
> +EXPORT_SYMBOL(dma_pseudo_bypass_ops);
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 17c590087279..d2ca214610fd 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -1088,6 +1088,7 @@ static struct pnv_ioda_pe *pnv_ioda_setup_dev_PE(struct pci_dev *dev)
>  	pe->pbus = NULL;
>  	pe->mve_number = -1;
>  	pe->rid = dev->bus->number << 8 | pdn->devfn;
> +	pe->tces = NULL;
>  
>  	pe_info(pe, "Associated device to PE\n");
>  
> @@ -1569,6 +1570,7 @@ static void pnv_ioda_setup_vf_PE(struct pci_dev *pdev, u16 num_vfs)
>  		pe->mve_number = -1;
>  		pe->rid = (pci_iov_virtfn_bus(pdev, vf_index) << 8) |
>  			   pci_iov_virtfn_devfn(pdev, vf_index);
> +		pe->tces = NULL;
>  
>  		pe_info(pe, "VF %04d:%02d:%02d.%d associated with PE#%x\n",
>  			hose->global_number, pdev->bus->number,
> @@ -1774,43 +1776,22 @@ static bool pnv_pci_ioda_pe_single_vendor(struct pnv_ioda_pe *pe)
>  	return true;
>  }
>  
> -/*
> - * Reconfigure TVE#0 to be usable as 64-bit DMA space.
> - *
> - * The first 4GB of virtual memory for a PE is reserved for 32-bit accesses.
> - * Devices can only access more than that if bit 59 of the PCI address is set
> - * by hardware, which indicates TVE#1 should be used instead of TVE#0.
> - * Many PCI devices are not capable of addressing that many bits, and as a
> - * result are limited to the 4GB of virtual memory made available to 32-bit
> - * devices in TVE#0.
> - *
> - * In order to work around this, reconfigure TVE#0 to be suitable for 64-bit
> - * devices by configuring the virtual memory past the first 4GB inaccessible
> - * by 64-bit DMAs.  This should only be used by devices that want more than
> - * 4GB, and only on PEs that have no 32-bit devices.
> - *
> - * Currently this will only work on PHB3 (POWER8).
> - */
> -static int pnv_pci_ioda_dma_64bit_bypass(struct pnv_ioda_pe *pe)
> +static int pnv_pci_pseudo_bypass_setup(struct pnv_ioda_pe *pe)
>  {
> -	u64 window_size, table_size, tce_count, addr;
> +	u64 tce_count, table_size, window_size;
> +	struct pnv_phb *p = pe->phb;
>  	struct page *table_pages;
> -	u64 tce_order = 28; /* 256MB TCEs */
>  	__be64 *tces;
> -	s64 rc;
> +	int rc = -ENOMEM;
>  
> -	/*
> -	 * Window size needs to be a power of two, but needs to account for
> -	 * shifting memory by the 4GB offset required to skip 32bit space.
> -	 */
> -	window_size = roundup_pow_of_two(memory_hotplug_max() + (1ULL << 32));
> -	tce_count = window_size >> tce_order;
> +	window_size = roundup_pow_of_two(memory_hotplug_max());
> +	tce_count = window_size >> p->ioda.max_tce_order;
>  	table_size = tce_count << 3;
>  
>  	if (table_size < PAGE_SIZE)
>  		table_size = PAGE_SIZE;
>  
> -	table_pages = alloc_pages_node(pe->phb->hose->node, GFP_KERNEL,
> +	table_pages = alloc_pages_node(p->hose->node, GFP_KERNEL,
>  				       get_order(table_size));
>  	if (!table_pages)
>  		goto err;
> @@ -1821,26 +1802,23 @@ static int pnv_pci_ioda_dma_64bit_bypass(struct pnv_ioda_pe *pe)
>  
>  	memset(tces, 0, table_size);
>  
> -	for (addr = 0; addr < memory_hotplug_max(); addr += (1 << tce_order)) {
> -		tces[(addr + (1ULL << 32)) >> tce_order] =
> -			cpu_to_be64(addr | TCE_PCI_READ | TCE_PCI_WRITE);
> -	}
> +	pe->tces = tces;
> +	pe->tce_count = tce_count;
>  
>  	rc = opal_pci_map_pe_dma_window(pe->phb->opal_id,
>  					pe->pe_number,
> -					/* reconfigure window 0 */
>  					(pe->pe_number << 1) + 0,
>  					1,
>  					__pa(tces),
>  					table_size,
> -					1 << tce_order);
> +					1 << p->ioda.max_tce_order);
>  	if (rc == OPAL_SUCCESS) {
> -		pe_info(pe, "Using 64-bit DMA iommu bypass (through TVE#0)\n");
> +		pe_info(pe, "TCE tables configured for pseudo-bypass\n");
>  		return 0;
>  	}
>  err:
> -	pe_err(pe, "Error configuring 64-bit DMA bypass\n");
> -	return -EIO;
> +	pe_err(pe, "error configuring pseudo-bypass\n");
> +	return rc;
>  }
>  
>  static int pnv_pci_ioda_dma_set_mask(struct pci_dev *pdev, u64 dma_mask)
> @@ -1851,7 +1829,6 @@ static int pnv_pci_ioda_dma_set_mask(struct pci_dev *pdev, u64 dma_mask)
>  	struct pnv_ioda_pe *pe;
>  	uint64_t top;
>  	bool bypass = false;
> -	s64 rc;
>  
>  	if (WARN_ON(!pdn || pdn->pe_number == IODA_INVALID_PE))
>  		return -ENODEV;
> @@ -1868,21 +1845,15 @@ static int pnv_pci_ioda_dma_set_mask(struct pci_dev *pdev, u64 dma_mask)
>  	} else {
>  		/*
>  		 * If the device can't set the TCE bypass bit but still wants
> -		 * to access 4GB or more, on PHB3 we can reconfigure TVE#0 to
> -		 * bypass the 32-bit region and be usable for 64-bit DMAs.
> -		 * The device needs to be able to address all of this space.
> +		 * to access 4GB or more, we need to use a different set of DMA
> +		 * operations with an indirect mapping.
>  		 */
>  		if (dma_mask >> 32 &&
> -		    dma_mask > (memory_hotplug_max() + (1ULL << 32)) &&
> -		    pnv_pci_ioda_pe_single_vendor(pe) &&
> -		    phb->model == PNV_PHB_MODEL_PHB3) {
> -			/* Configure the bypass mode */
> -			rc = pnv_pci_ioda_dma_64bit_bypass(pe);
> -			if (rc)
> -				return rc;
> -			/* 4GB offset bypasses 32-bit space */
> -			set_dma_offset(&pdev->dev, (1ULL << 32));
> -			set_dma_ops(&pdev->dev, &dma_nommu_ops);
> +		    phb->model != PNV_PHB_MODEL_P7IOC &&
> +		    pnv_pci_ioda_pe_single_vendor(pe)) {
> +			if (!pe->tces)
> +				pnv_pci_pseudo_bypass_setup(pe);
> +			set_dma_ops(&pdev->dev, &dma_pseudo_bypass_ops);
>  		} else if (dma_mask >> 32 && dma_mask != DMA_BIT_MASK(64)) {
>  			/*
>  			 * Fail the request if a DMA mask between 32 and 64 bits
> @@ -2071,7 +2042,7 @@ static inline void pnv_pci_phb3_tce_invalidate_pe(struct pnv_ioda_pe *pe)
>  	__raw_writeq_be(val, invalidate);
>  }
>  
> -static void pnv_pci_phb3_tce_invalidate(struct pnv_ioda_pe *pe, bool rm,
> +void pnv_pci_phb3_tce_invalidate(struct pnv_ioda_pe *pe, bool rm,
>  					unsigned shift, unsigned long index,
>  					unsigned long npages)
>  {
> @@ -2611,10 +2582,15 @@ static unsigned long pnv_pci_ioda2_get_table_size(__u32 page_shift,
>  static void pnv_ioda2_take_ownership(struct iommu_table_group *table_group)
>  {
>  	struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> -						table_group);
> +					      table_group);
> +
>  	/* Store @tbl as pnv_pci_ioda2_unset_window() resets it */
>  	struct iommu_table *tbl = pe->table_group.tables[0];
>  
> +	if (pe->tces)
> +		free_pages((unsigned long)pe->tces,
> +			   get_order(pe->tce_count << 3));
> +
>  	pnv_pci_ioda2_set_bypass(pe, false);
>  	pnv_pci_ioda2_unset_window(&pe->table_group, 0);
>  	if (pe->pbus)
> diff --git a/arch/powerpc/platforms/powernv/pci.h b/arch/powerpc/platforms/powernv/pci.h
> index c9952def5e93..56846ddc76a2 100644
> --- a/arch/powerpc/platforms/powernv/pci.h
> +++ b/arch/powerpc/platforms/powernv/pci.h
> @@ -70,6 +70,10 @@ struct pnv_ioda_pe {
>  	bool			tce_bypass_enabled;
>  	uint64_t		tce_bypass_base;
>  
> +	/* TCE tables for DMA pseudo-bypass */
> +	__be64			*tces;
> +	u64			tce_count;
> +
>  	/* MSIs. MVE index is identical for for 32 and 64 bit MSI
>  	 * and -1 if not supported. (It's actually identical to the
>  	 * PE number)
> @@ -211,6 +215,9 @@ extern void pnv_tce_free(struct iommu_table *tbl, long index, long npages);
>  extern int pnv_tce_xchg(struct iommu_table *tbl, long index,
>  		unsigned long *hpa, enum dma_data_direction *direction);
>  extern unsigned long pnv_tce_get(struct iommu_table *tbl, long index);
> +extern void pnv_pci_phb3_tce_invalidate(struct pnv_ioda_pe *pe, bool rm,
> +					unsigned shift, unsigned long index,
> +					unsigned long npages);
>  
>  void pnv_pci_dump_phb_diag_data(struct pci_controller *hose,
>  				unsigned char *log_buff);

On Fri, 29 Jun 2018 17:34:36 +1000
Russell Currey <ruscur@russell.cc> wrote:

> DMA pseudo-bypass is a new set of DMA operations that solve some issues for
> devices that want to address more than 32 bits but can't address the 59
> bits required to enable direct DMA.
> 
> The previous implementation for POWER8/PHB3 worked around this by
> configuring a bypass from the default 32-bit address space into 64-bit
> address space.  This approach does not work for POWER9/PHB4 because
> regions of memory are discontiguous and many devices will be unable to
> address memory beyond the first node.
> 
> Instead, implement a new set of DMA operations that allocate TCEs as DMA
> mappings are requested so that all memory is addressable even when a
> one-to-one mapping between real addresses and DMA addresses isn't
> possible.  These TCEs are the maximum size available on the platform,
> which is 256M on PHB3 and 1G on PHB4.
> 
> Devices can now map any region of memory up to the maximum amount they can
> address according to the DMA mask set, in chunks of the largest available
> TCE size.
> 
> This implementation replaces the need for the existing PHB3 solution and
> should be compatible with future PHB versions.
> 
> It is, however, rather naive.  There is no unmapping, and as a result
> devices can eventually run out of space if they address their entire
> DMA mask worth of TCEs.  An implementation with unmap() will come in
> future (and requires a much more complex implementation), but this is a
> good start due to the drastic performance improvement.


Why does not dma_iommu_ops work in this case? I keep asking and yet no
comment in the commit log or mails...


> 
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> ---
>  arch/powerpc/include/asm/dma-mapping.h    |   1 +
>  arch/powerpc/platforms/powernv/Makefile   |   2 +-
>  arch/powerpc/platforms/powernv/pci-dma.c  | 243 ++++++++++++++++++++++
>  arch/powerpc/platforms/powernv/pci-ioda.c |  82 +++-----
>  arch/powerpc/platforms/powernv/pci.h      |   7 +
>  5 files changed, 281 insertions(+), 54 deletions(-)
>  create mode 100644 arch/powerpc/platforms/powernv/pci-dma.c

Too generic file name for such a hack.


> 
> diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h
> index 8fa394520af6..354f435160f3 100644
> --- a/arch/powerpc/include/asm/dma-mapping.h
> +++ b/arch/powerpc/include/asm/dma-mapping.h
> @@ -74,6 +74,7 @@ static inline unsigned long device_to_mask(struct device *dev)
>  extern struct dma_map_ops dma_iommu_ops;
>  #endif
>  extern const struct dma_map_ops dma_nommu_ops;
> +extern const struct dma_map_ops dma_pseudo_bypass_ops;
>  
>  static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
>  {
> diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
> index 703a350a7f4e..2467bdab3c13 100644
> --- a/arch/powerpc/platforms/powernv/Makefile
> +++ b/arch/powerpc/platforms/powernv/Makefile
> @@ -6,7 +6,7 @@ obj-y			+= opal-msglog.o opal-hmi.o opal-power.o opal-irqchip.o
>  obj-y			+= opal-kmsg.o opal-powercap.o opal-psr.o opal-sensor-groups.o
>  
>  obj-$(CONFIG_SMP)	+= smp.o subcore.o subcore-asm.o
> -obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o
> +obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o pci-dma.o
>  obj-$(CONFIG_CXL_BASE)	+= pci-cxl.o
>  obj-$(CONFIG_EEH)	+= eeh-powernv.o
>  obj-$(CONFIG_PPC_SCOM)	+= opal-xscom.o
> diff --git a/arch/powerpc/platforms/powernv/pci-dma.c b/arch/powerpc/platforms/powernv/pci-dma.c
> new file mode 100644
> index 000000000000..79382627c7be
> --- /dev/null
> +++ b/arch/powerpc/platforms/powernv/pci-dma.c
> @@ -0,0 +1,243 @@
> +/*
> + * DMA operations supporting pseudo-bypass for PHB3+
> + *
> + * Author: Russell Currey <ruscur@russell.cc>
> + *
> + * Copyright 2018 IBM Corporation.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the
> + * Free Software Foundation; either version 2 of the License, or (at your
> + * option) any later version.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/memblock.h>
> +#include <linux/device.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/hash.h>
> +
> +#include <asm/pci-bridge.h>
> +#include <asm/ppc-pci.h>
> +#include <asm/pnv-pci.h>
> +#include <asm/tce.h>
> +
> +#include "pci.h"
> +
> +/*
> + * This is a naive implementation that directly operates on TCEs, allocating
> + * on demand.  There is no locking or refcounts since no TCEs are ever removed
> + * and unmap does nothing.
> + */
> +static dma_addr_t dma_pseudo_bypass_get_address(struct device *dev,
> +					    phys_addr_t addr)
> +{
> +	struct pci_dev *pdev = container_of(dev, struct pci_dev, dev);
> +	struct pci_controller *hose = pci_bus_to_host(pdev->bus);
> +	struct pnv_phb *phb = hose->private_data;
> +	struct pnv_ioda_pe *pe;
> +	u64 i, tce, ret, offset;
> +	__be64 entry;
> +
> +	offset = addr & ((1 << phb->ioda.max_tce_order) - 1);
> +
> +	pe = &phb->ioda.pe_array[pci_get_pdn(pdev)->pe_number];
> +
> +	/* look through the tracking table for a free entry */
> +	for (i = 0; i < pe->tce_count; i++) {
> +		/* skip between 2GB and 4GB */
> +		if ((i << phb->ioda.max_tce_order) >= 0x80000000 &&
> +		    (i << phb->ioda.max_tce_order) < 0x100000000)
> +			continue;
> +
> +		tce = be64_to_cpu(pe->tces[i]);
> +
> +		/* if the TCE is already valid (read + write) */
> +		if ((tce & 3) == 3) {
> +			/* check if we're already allocated, if not move on */
> +			if (tce >> phb->ioda.max_tce_order ==
> +			    addr >> phb->ioda.max_tce_order) {
> +				/* wait for the lock bit to clear */
> +				while (be64_to_cpu(pe->tces[i]) & 4)
> +					cpu_relax();
> +
> +				return (i << phb->ioda.max_tce_order) | offset;
> +			}
> +
> +			continue;
> +		}
> +
> +		/*
> +		 * The TCE isn't being used, so let's try and allocate it.
> +		 * Bits 0 and 1 are read/write, and we use bit 2 as a "lock"
> +		 * bit.  This is to prevent any race where the value is set in
> +		 * the TCE table but the invalidate/mb() hasn't finished yet.
> +		 */
> +		entry = cpu_to_be64((addr - offset) | 7);
> +		ret = cmpxchg(&pe->tces[i], tce, entry);
> +		if (ret != tce) {
> +			/* conflict, start looking again just in case */
> +			i--;
> +			continue;
> +		}
> +		pnv_pci_phb3_tce_invalidate(pe, 0, 0, addr - offset, 1);
> +		mb();
> +		/* clear the lock bit now that we know it's active */
> +		ret = cmpxchg(&pe->tces[i], entry, cpu_to_be64((addr - offset) | 3));
> +		if (ret != entry) {
> +			/* conflict, start looking again just in case */
> +			i--;
> +			continue;
> +		}
> +
> +		return (i << phb->ioda.max_tce_order) | offset;
> +	}
> +	/* If we get here, the table must be full, so error out. */
> +	return -1ULL;
> +}
> +
> +/*
> + * For now, don't actually do anything on unmap.
> + */
> +static void dma_pseudo_bypass_unmap_address(struct device *dev, dma_addr_t dma_addr)
> +{
> +}
> +
> +static int dma_pseudo_bypass_dma_supported(struct device *dev, u64 mask)
> +{
> +	/*
> +	 * Normally dma_supported() checks if the mask is capable of addressing
> +	 * all of memory.  Since we map physical memory in chunks that the
> +	 * device can address, the device will be able to address whatever it
> +	 * wants - just not all at once.
> +	 */
> +	return 1;
> +}
> +
> +static void *dma_pseudo_bypass_alloc_coherent(struct device *dev,
> +					  size_t size,
> +					  dma_addr_t *dma_handle,
> +					  gfp_t flag,
> +					  unsigned long attrs)
> +{
> +	void *ret;
> +	struct page *page;
> +	int node = dev_to_node(dev);
> +
> +	/* ignore region specifiers */
> +	flag &= ~(__GFP_HIGHMEM);
> +
> +	page = alloc_pages_node(node, flag, get_order(size));
> +	if (page == NULL)
> +		return NULL;
> +	ret = page_address(page);
> +	memset(ret, 0, size);
> +	*dma_handle = dma_pseudo_bypass_get_address(dev, __pa(ret));
> +
> +	return ret;
> +}
> +
> +static void dma_pseudo_bypass_free_coherent(struct device *dev,
> +					 size_t size,
> +					 void *vaddr,
> +					 dma_addr_t dma_handle,
> +					 unsigned long attrs)
> +{
> +	free_pages((unsigned long)vaddr, get_order(size));
> +}
> +
> +static int dma_pseudo_bypass_mmap_coherent(struct device *dev,
> +				       struct vm_area_struct *vma,
> +				       void *cpu_addr,
> +				       dma_addr_t handle,
> +				       size_t size,
> +				       unsigned long attrs)
> +{
> +	unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
> +
> +	return remap_pfn_range(vma, vma->vm_start,
> +			       pfn + vma->vm_pgoff,
> +			       vma->vm_end - vma->vm_start,
> +			       vma->vm_page_prot);
> +}
> +
> +static inline dma_addr_t dma_pseudo_bypass_map_page(struct device *dev,
> +						struct page *page,
> +						unsigned long offset,
> +						size_t size,
> +						enum dma_data_direction dir,
> +						unsigned long attrs)
> +{
> +	BUG_ON(dir == DMA_NONE);
> +
> +	return dma_pseudo_bypass_get_address(dev, page_to_phys(page) + offset);
> +}
> +
> +static inline void dma_pseudo_bypass_unmap_page(struct device *dev,
> +					 dma_addr_t dma_address,
> +					 size_t size,
> +					 enum dma_data_direction direction,
> +					 unsigned long attrs)
> +{
> +	dma_pseudo_bypass_unmap_address(dev, dma_address);
> +}
> +
> +
> +static int dma_pseudo_bypass_map_sg(struct device *dev, struct scatterlist *sgl,
> +			     int nents, enum dma_data_direction direction,
> +			     unsigned long attrs)
> +{
> +	struct scatterlist *sg;
> +	int i;
> +
> +
> +	for_each_sg(sgl, sg, nents, i) {
> +		sg->dma_address = dma_pseudo_bypass_get_address(dev, sg_phys(sg));
> +		sg->dma_length = sg->length;
> +
> +		__dma_sync_page(sg_page(sg), sg->offset, sg->length, direction);
> +	}
> +
> +	return nents;
> +}
> +
> +static void dma_pseudo_bypass_unmap_sg(struct device *dev, struct scatterlist *sgl,
> +				int nents, enum dma_data_direction direction,
> +				unsigned long attrs)
> +{
> +	struct scatterlist *sg;
> +	int i;
> +
> +	for_each_sg(sgl, sg, nents, i) {
> +		dma_pseudo_bypass_unmap_address(dev, sg->dma_address);
> +	}
> +}
> +
> +static u64 dma_pseudo_bypass_get_required_mask(struct device *dev)
> +{
> +	/*
> +	 * there's no limitation on our end, the driver should just call
> +	 * set_mask() with as many bits as the device can address.
> +	 */
> +	return -1ULL;
> +}
> +
> +static int dma_pseudo_bypass_mapping_error(struct device *dev, dma_addr_t dma_addr)
> +{
> +	return dma_addr == -1ULL;




> +}
> +
> +
> +const struct dma_map_ops dma_pseudo_bypass_ops = {
> +	.alloc				= dma_pseudo_bypass_alloc_coherent,
> +	.free				= dma_pseudo_bypass_free_coherent,
> +	.mmap				= dma_pseudo_bypass_mmap_coherent,
> +	.map_sg				= dma_pseudo_bypass_map_sg,
> +	.unmap_sg			= dma_pseudo_bypass_unmap_sg,
> +	.dma_supported			= dma_pseudo_bypass_dma_supported,
> +	.map_page			= dma_pseudo_bypass_map_page,
> +	.unmap_page			= dma_pseudo_bypass_unmap_page,
> +	.get_required_mask		= dma_pseudo_bypass_get_required_mask,
> +	.mapping_error			= dma_pseudo_bypass_mapping_error,
> +};
> +EXPORT_SYMBOL(dma_pseudo_bypass_ops);
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 17c590087279..d2ca214610fd 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -1088,6 +1088,7 @@ static struct pnv_ioda_pe *pnv_ioda_setup_dev_PE(struct pci_dev *dev)
>  	pe->pbus = NULL;
>  	pe->mve_number = -1;
>  	pe->rid = dev->bus->number << 8 | pdn->devfn;
> +	pe->tces = NULL;
>  
>  	pe_info(pe, "Associated device to PE\n");
>  
> @@ -1569,6 +1570,7 @@ static void pnv_ioda_setup_vf_PE(struct pci_dev *pdev, u16 num_vfs)
>  		pe->mve_number = -1;
>  		pe->rid = (pci_iov_virtfn_bus(pdev, vf_index) << 8) |
>  			   pci_iov_virtfn_devfn(pdev, vf_index);
> +		pe->tces = NULL;
>  
>  		pe_info(pe, "VF %04d:%02d:%02d.%d associated with PE#%x\n",
>  			hose->global_number, pdev->bus->number,
> @@ -1774,43 +1776,22 @@ static bool pnv_pci_ioda_pe_single_vendor(struct pnv_ioda_pe *pe)
>  	return true;
>  }
>  
> -/*
> - * Reconfigure TVE#0 to be usable as 64-bit DMA space.
> - *
> - * The first 4GB of virtual memory for a PE is reserved for 32-bit accesses.
> - * Devices can only access more than that if bit 59 of the PCI address is set
> - * by hardware, which indicates TVE#1 should be used instead of TVE#0.
> - * Many PCI devices are not capable of addressing that many bits, and as a
> - * result are limited to the 4GB of virtual memory made available to 32-bit
> - * devices in TVE#0.
> - *
> - * In order to work around this, reconfigure TVE#0 to be suitable for 64-bit
> - * devices by configuring the virtual memory past the first 4GB inaccessible
> - * by 64-bit DMAs.  This should only be used by devices that want more than
> - * 4GB, and only on PEs that have no 32-bit devices.
> - *
> - * Currently this will only work on PHB3 (POWER8).
> - */
> -static int pnv_pci_ioda_dma_64bit_bypass(struct pnv_ioda_pe *pe)
> +static int pnv_pci_pseudo_bypass_setup(struct pnv_ioda_pe *pe)
>  {
> -	u64 window_size, table_size, tce_count, addr;
> +	u64 tce_count, table_size, window_size;
> +	struct pnv_phb *p = pe->phb;
>  	struct page *table_pages;
> -	u64 tce_order = 28; /* 256MB TCEs */
>  	__be64 *tces;
> -	s64 rc;
> +	int rc = -ENOMEM;
>  
> -	/*
> -	 * Window size needs to be a power of two, but needs to account for
> -	 * shifting memory by the 4GB offset required to skip 32bit space.
> -	 */
> -	window_size = roundup_pow_of_two(memory_hotplug_max() + (1ULL << 32));
> -	tce_count = window_size >> tce_order;
> +	window_size = roundup_pow_of_two(memory_hotplug_max());
> +	tce_count = window_size >> p->ioda.max_tce_order;
>  	table_size = tce_count << 3;
>  
>  	if (table_size < PAGE_SIZE)
>  		table_size = PAGE_SIZE;
>  
> -	table_pages = alloc_pages_node(pe->phb->hose->node, GFP_KERNEL,
> +	table_pages = alloc_pages_node(p->hose->node, GFP_KERNEL,
>  				       get_order(table_size));


pnv_pci_ioda2_create_table() allocates the table, why does not it work for this task?


>  	if (!table_pages)
>  		goto err;
> @@ -1821,26 +1802,23 @@ static int pnv_pci_ioda_dma_64bit_bypass(struct pnv_ioda_pe *pe)
>  
>  	memset(tces, 0, table_size);
>  
> -	for (addr = 0; addr < memory_hotplug_max(); addr += (1 << tce_order)) {
> -		tces[(addr + (1ULL << 32)) >> tce_order] =
> -			cpu_to_be64(addr | TCE_PCI_READ | TCE_PCI_WRITE);
> -	}
> +	pe->tces = tces;
> +	pe->tce_count = tce_count;
>  
>  	rc = opal_pci_map_pe_dma_window(pe->phb->opal_id,
>  					pe->pe_number,
> -					/* reconfigure window 0 */
>  					(pe->pe_number << 1) + 0,
>  					1,
>  					__pa(tces),
>  					table_size,
> -					1 << tce_order);
> +					1 << p->ioda.max_tce_order);
>  	if (rc == OPAL_SUCCESS) {
> -		pe_info(pe, "Using 64-bit DMA iommu bypass (through TVE#0)\n");
> +		pe_info(pe, "TCE tables configured for pseudo-bypass\n");
>  		return 0;
>  	}
>  err:
> -	pe_err(pe, "Error configuring 64-bit DMA bypass\n");
> -	return -EIO;
> +	pe_err(pe, "error configuring pseudo-bypass\n");
> +	return rc;
>  }
>  
>  static int pnv_pci_ioda_dma_set_mask(struct pci_dev *pdev, u64 dma_mask)
> @@ -1851,7 +1829,6 @@ static int pnv_pci_ioda_dma_set_mask(struct pci_dev *pdev, u64 dma_mask)
>  	struct pnv_ioda_pe *pe;
>  	uint64_t top;
>  	bool bypass = false;
> -	s64 rc;
>  
>  	if (WARN_ON(!pdn || pdn->pe_number == IODA_INVALID_PE))
>  		return -ENODEV;
> @@ -1868,21 +1845,15 @@ static int pnv_pci_ioda_dma_set_mask(struct pci_dev *pdev, u64 dma_mask)
>  	} else {
>  		/*
>  		 * If the device can't set the TCE bypass bit but still wants
> -		 * to access 4GB or more, on PHB3 we can reconfigure TVE#0 to
> -		 * bypass the 32-bit region and be usable for 64-bit DMAs.
> -		 * The device needs to be able to address all of this space.
> +		 * to access 4GB or more, we need to use a different set of DMA
> +		 * operations with an indirect mapping.
>  		 */
>  		if (dma_mask >> 32 &&
> -		    dma_mask > (memory_hotplug_max() + (1ULL << 32)) &&
> -		    pnv_pci_ioda_pe_single_vendor(pe) &&
> -		    phb->model == PNV_PHB_MODEL_PHB3) {
> -			/* Configure the bypass mode */
> -			rc = pnv_pci_ioda_dma_64bit_bypass(pe);
> -			if (rc)
> -				return rc;
> -			/* 4GB offset bypasses 32-bit space */
> -			set_dma_offset(&pdev->dev, (1ULL << 32));
> -			set_dma_ops(&pdev->dev, &dma_nommu_ops);
> +		    phb->model != PNV_PHB_MODEL_P7IOC &&
> +		    pnv_pci_ioda_pe_single_vendor(pe)) {
> +			if (!pe->tces)
> +				pnv_pci_pseudo_bypass_setup(pe);
> +			set_dma_ops(&pdev->dev, &dma_pseudo_bypass_ops);
>  		} else if (dma_mask >> 32 && dma_mask != DMA_BIT_MASK(64)) {
>  			/*
>  			 * Fail the request if a DMA mask between 32 and 64 bits
> @@ -2071,7 +2042,7 @@ static inline void pnv_pci_phb3_tce_invalidate_pe(struct pnv_ioda_pe *pe)
>  	__raw_writeq_be(val, invalidate);
>  }
>  
> -static void pnv_pci_phb3_tce_invalidate(struct pnv_ioda_pe *pe, bool rm,
> +void pnv_pci_phb3_tce_invalidate(struct pnv_ioda_pe *pe, bool rm,
>  					unsigned shift, unsigned long index,
>  					unsigned long npages)
>  {
> @@ -2611,10 +2582,15 @@ static unsigned long pnv_pci_ioda2_get_table_size(__u32 page_shift,
>  static void pnv_ioda2_take_ownership(struct iommu_table_group *table_group)
>  {
>  	struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> -						table_group);
> +					      table_group);
> +
>  	/* Store @tbl as pnv_pci_ioda2_unset_window() resets it */
>  	struct iommu_table *tbl = pe->table_group.tables[0];
>  
> +	if (pe->tces)
> +		free_pages((unsigned long)pe->tces,
> +			   get_order(pe->tce_count << 3));
> +
>  	pnv_pci_ioda2_set_bypass(pe, false);
>  	pnv_pci_ioda2_unset_window(&pe->table_group, 0);
>  	if (pe->pbus)
> diff --git a/arch/powerpc/platforms/powernv/pci.h b/arch/powerpc/platforms/powernv/pci.h
> index c9952def5e93..56846ddc76a2 100644
> --- a/arch/powerpc/platforms/powernv/pci.h
> +++ b/arch/powerpc/platforms/powernv/pci.h
> @@ -70,6 +70,10 @@ struct pnv_ioda_pe {
>  	bool			tce_bypass_enabled;
>  	uint64_t		tce_bypass_base;
>  
> +	/* TCE tables for DMA pseudo-bypass */
> +	__be64			*tces;
> +	u64			tce_count;


pnv_ioda_pe::table_group::tables[0] has a pointer to pages, a table size in entries and a page size, why duplicate all of this again?


> +
>  	/* MSIs. MVE index is identical for for 32 and 64 bit MSI
>  	 * and -1 if not supported. (It's actually identical to the
>  	 * PE number)
> @@ -211,6 +215,9 @@ extern void pnv_tce_free(struct iommu_table *tbl, long index, long npages);
>  extern int pnv_tce_xchg(struct iommu_table *tbl, long index,
>  		unsigned long *hpa, enum dma_data_direction *direction);
>  extern unsigned long pnv_tce_get(struct iommu_table *tbl, long index);
> +extern void pnv_pci_phb3_tce_invalidate(struct pnv_ioda_pe *pe, bool rm,
> +					unsigned shift, unsigned long index,
> +					unsigned long npages);
>  
>  void pnv_pci_dump_phb_diag_data(struct pci_controller *hose,
>  				unsigned char *log_buff);
> -- 
> 2.17.1
> 



--
Alexey

On Mon, 2018-07-02 at 18:47 +1000, Alexey Kardashevskiy wrote:
> On Fri, 29 Jun 2018 17:34:36 +1000
> Russell Currey <ruscur@russell.cc> wrote:
> 
> > DMA pseudo-bypass is a new set of DMA operations that solve some
> > issues for
> > devices that want to address more than 32 bits but can't address
> > the 59
> > bits required to enable direct DMA.
> > 
> > The previous implementation for POWER8/PHB3 worked around this by
> > configuring a bypass from the default 32-bit address space into 64-
> > bit
> > address space.  This approach does not work for POWER9/PHB4 because
> > regions of memory are discontiguous and many devices will be unable
> > to
> > address memory beyond the first node.
> > 
> > Instead, implement a new set of DMA operations that allocate TCEs
> > as DMA
> > mappings are requested so that all memory is addressable even when
> > a
> > one-to-one mapping between real addresses and DMA addresses isn't
> > possible.  These TCEs are the maximum size available on the
> > platform,
> > which is 256M on PHB3 and 1G on PHB4.
> > 
> > Devices can now map any region of memory up to the maximum amount
> > they can
> > address according to the DMA mask set, in chunks of the largest
> > available
> > TCE size.
> > 
> > This implementation replaces the need for the existing PHB3
> > solution and
> > should be compatible with future PHB versions.
> > 
> > It is, however, rather naive.  There is no unmapping, and as a
> > result
> > devices can eventually run out of space if they address their
> > entire
> > DMA mask worth of TCEs.  An implementation with unmap() will come
> > in
> > future (and requires a much more complex implementation), but this
> > is a
> > good start due to the drastic performance improvement.
> 
> 
> Why does not dma_iommu_ops work in this case? I keep asking and yet
> no
> comment in the commit log or mails...

Yes, I should cover this in the commit message.

So the primary reason that the IOMMU doesn't work for this case is the
TCE allocation - the IOMMU doesn't have a refcount and will allocate
(in this case on P9) 1GB TCEs to each map which will quickly fail.

This isn't intended to be a replacement for the IOMMU, it's a
roundabout way of achieving what the direct ops do (like NVIDIA devices
on P8 can do today).

On Fri, 2018-06-29 at 17:34 +1000, Russell Currey wrote:

<snip>

> +		/*
> +		 * The TCE isn't being used, so let's try and
> allocate it.
> +		 * Bits 0 and 1 are read/write, and we use bit 2 as
> a "lock"
> +		 * bit.  This is to prevent any race where the value
> is set in
> +		 * the TCE table but the invalidate/mb() hasn't
> finished yet.
> +		 */
> +		entry = cpu_to_be64((addr - offset) | 7);
> +		ret = cmpxchg(&pe->tces[i], tce, entry);
> +		if (ret != tce) {
> +			/* conflict, start looking again just in
> case */
> +			i--;
> +			continue;
> +		}
> +		pnv_pci_phb3_tce_invalidate(pe, 0, 0, addr - offset,
> 1);

This is wrong and won't work outside of PHB3, will make a generic
handler

> +		mb();
> +		/* clear the lock bit now that we know it's active
> */
> +		ret = cmpxchg(&pe->tces[i], entry, cpu_to_be64((addr
> - offset) | 3));
> +		if (ret != entry) {
> +			/* conflict, start looking again just in
> case */
> +			i--;
> +			continue;
> +		}
> +
> +		return (i << phb->ioda.max_tce_order) | offset;
> +	}
> +	/* If we get here, the table must be full, so error out. */
> +	return -1ULL;
> +}
> +