[v4,3/3] i2c: mux: pca954x: allow management of device idle state via sysfs
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Message ID 20190228114343.36443-4-robertshearman@gmail.com
State Accepted
Delegated to: Peter Rosin
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Series
  • i2c: mux: pca954x: allow management of device idle state via sysfs
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Commit Message

Robert Shearman Feb. 28, 2019, 11:43 a.m. UTC
From: Robert Shearman <robert.shearman@att.com>

The behaviour, by default, to not deselect after each transfer is
unsafe when there is a device with an address that conflicts with
another device on another mux on the same parent bus, and it
may not be convenient to use devicetree to set the deselect mux,
e.g. when running on x86_64 when ACPI is used to discover most of the
device hierarchy.

Therefore, provide the ability to set the idle state behaviour using a
new sysfs file, idle_state as a complement to the method of
instantiating the device via sysfs. The possible behaviours are
disconnect, i.e. to deselect all channels from the mux, as-is (the
default), i.e. leave the last channel selected, and set a
predetermined channel.

The current behaviour of leaving the channel as-is after each
transaction is preserved.

Signed-off-by: Robert Shearman <robert.shearman@att.com>
---
 .../ABI/testing/sysfs-bus-i2c-devices-pca954x | 20 +++++
 drivers/i2c/muxes/i2c-mux-pca954x.c           | 85 +++++++++++++++++--
 2 files changed, 97 insertions(+), 8 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x

Comments

Peter Rosin March 13, 2019, 7:04 a.m. UTC | #1
Hi Greg,

I was wondering if you think the below ABI addition looks sane to you?
Or, should I ask someone else for a tag?

Cheers,
Peter

On 2019-02-28 12:43, Robert Shearman wrote:
> From: Robert Shearman <robert.shearman@att.com>
> 
> The behaviour, by default, to not deselect after each transfer is
> unsafe when there is a device with an address that conflicts with
> another device on another mux on the same parent bus, and it
> may not be convenient to use devicetree to set the deselect mux,
> e.g. when running on x86_64 when ACPI is used to discover most of the
> device hierarchy.
> 
> Therefore, provide the ability to set the idle state behaviour using a
> new sysfs file, idle_state as a complement to the method of
> instantiating the device via sysfs. The possible behaviours are
> disconnect, i.e. to deselect all channels from the mux, as-is (the
> default), i.e. leave the last channel selected, and set a
> predetermined channel.
> 
> The current behaviour of leaving the channel as-is after each
> transaction is preserved.
> 
> Signed-off-by: Robert Shearman <robert.shearman@att.com>
> ---
>  .../ABI/testing/sysfs-bus-i2c-devices-pca954x | 20 +++++
>  drivers/i2c/muxes/i2c-mux-pca954x.c           | 85 +++++++++++++++++--
>  2 files changed, 97 insertions(+), 8 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x b/Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x
> new file mode 100644
> index 000000000000..0b0de8cd0d13
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x
> @@ -0,0 +1,20 @@
> +What:		/sys/bus/i2c/.../idle_state
> +Date:		January 2019
> +KernelVersion:	5.2
> +Contact:	Robert Shearman <robert.shearman@att.com>
> +Description:
> +		Value that exists only for mux devices that can be
> +		written to control the behaviour of the multiplexer on
> +		idle. Possible values:
> +		-2 - disconnect on idle, i.e. deselect the last used
> +		     channel, which is useful when there is a device
> +		     with an address that conflicts with another
> +		     device on another mux on the same parent bus.
> +		-1 - leave the mux as-is, which is the most optimal
> +		     setting in terms of I2C operations and is the
> +		     default mode.
> +		0..<nchans> - set the mux to a predetermined channel,
> +		     which is useful if there is one channel that is
> +		     used almost always, and you want to reduce the
> +		     latency for normal operations after rare
> +		     transactions on other channels
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index e32fef560684..923aa3a5a3dc 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -49,6 +49,7 @@
>  #include <linux/pm.h>
>  #include <linux/slab.h>
>  #include <linux/spinlock.h>
> +#include <dt-bindings/mux/mux.h>
>  
>  #define PCA954X_MAX_NCHANS 8
>  
> @@ -84,7 +85,9 @@ struct pca954x {
>  	const struct chip_desc *chip;
>  
>  	u8 last_chan;		/* last register value */
> -	u8 deselect;
> +	/* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
> +	s8 idle_state;
> +
>  	struct i2c_client *client;
>  
>  	struct irq_domain *irq;
> @@ -253,15 +256,71 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
>  {
>  	struct pca954x *data = i2c_mux_priv(muxc);
>  	struct i2c_client *client = data->client;
> +	s8 idle_state;
> +
> +	idle_state = READ_ONCE(data->idle_state);
> +	if (idle_state >= 0)
> +		/* Set the mux back to a predetermined channel */
> +		return pca954x_select_chan(muxc, idle_state);
> +
> +	if (idle_state == MUX_IDLE_DISCONNECT) {
> +		/* Deselect active channel */
> +		data->last_chan = 0;
> +		return pca954x_reg_write(muxc->parent, client,
> +					 data->last_chan);
> +	}
>  
> -	if (!(data->deselect & (1 << chan)))
> -		return 0;
> +	/* otherwise leave as-is */
>  
> -	/* Deselect active channel */
> -	data->last_chan = 0;
> -	return pca954x_reg_write(muxc->parent, client, data->last_chan);
> +	return 0;
> +}
> +
> +static ssize_t idle_state_show(struct device *dev,
> +				    struct device_attribute *attr,
> +				    char *buf)
> +{
> +	struct i2c_client *client = to_i2c_client(dev);
> +	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
> +	struct pca954x *data = i2c_mux_priv(muxc);
> +
> +	return sprintf(buf, "%d\n", READ_ONCE(data->idle_state));
> +}
> +
> +static ssize_t idle_state_store(struct device *dev,
> +				struct device_attribute *attr,
> +				const char *buf, size_t count)
> +{
> +	struct i2c_client *client = to_i2c_client(dev);
> +	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
> +	struct pca954x *data = i2c_mux_priv(muxc);
> +	int val;
> +	int ret;
> +
> +	ret = kstrtoint(buf, 0, &val);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (val != MUX_IDLE_AS_IS && val != MUX_IDLE_DISCONNECT &&
> +	    (val < 0 || val >= data->chip->nchans))
> +		return -EINVAL;
> +
> +	i2c_lock_bus(muxc->parent, I2C_LOCK_SEGMENT);
> +
> +	WRITE_ONCE(data->idle_state, val);
> +	/*
> +	 * Set the mux into a state consistent with the new
> +	 * idle_state.
> +	 */
> +	if (data->last_chan || val != MUX_IDLE_DISCONNECT)
> +		ret = pca954x_deselect_mux(muxc, 0);
> +
> +	i2c_unlock_bus(muxc->parent, I2C_LOCK_SEGMENT);
> +
> +	return ret < 0 ? ret : count;
>  }
>  
> +static DEVICE_ATTR_RW(idle_state);
> +
>  static irqreturn_t pca954x_irq_handler(int irq, void *dev_id)
>  {
>  	struct pca954x *data = dev_id;
> @@ -328,8 +387,11 @@ static int pca954x_irq_setup(struct i2c_mux_core *muxc)
>  static void pca954x_cleanup(struct i2c_mux_core *muxc)
>  {
>  	struct pca954x *data = i2c_mux_priv(muxc);
> +	struct i2c_client *client = data->client;
>  	int c, irq;
>  
> +	device_remove_file(&client->dev, &dev_attr_idle_state);
> +
>  	if (data->irq) {
>  		for (c = 0; c < data->chip->nchans; c++) {
>  			irq = irq_find_mapping(data->irq, c);
> @@ -410,9 +472,12 @@ static int pca954x_probe(struct i2c_client *client,
>  	}
>  
>  	data->last_chan = 0;		   /* force the first selection */
> +	data->idle_state = MUX_IDLE_AS_IS;
>  
>  	idle_disconnect_dt = np &&
>  		of_property_read_bool(np, "i2c-mux-idle-disconnect");
> +	if (idle_disconnect_dt)
> +		data->idle_state = MUX_IDLE_DISCONNECT;
>  
>  	ret = pca954x_irq_setup(muxc);
>  	if (ret)
> @@ -420,8 +485,6 @@ static int pca954x_probe(struct i2c_client *client,
>  
>  	/* Now create an adapter for each channel */
>  	for (num = 0; num < data->chip->nchans; num++) {
> -		data->deselect |= idle_disconnect_dt << num;
> -
>  		ret = i2c_mux_add_adapter(muxc, 0, num, 0);
>  		if (ret)
>  			goto fail_cleanup;
> @@ -436,6 +499,12 @@ static int pca954x_probe(struct i2c_client *client,
>  			goto fail_cleanup;
>  	}
>  
> +	/*
> +	 * The attr probably isn't going to be needed in most cases,
> +	 * so don't fail completely on error.
> +	 */
> +	device_create_file(dev, &dev_attr_idle_state);
> +
>  	dev_info(dev, "registered %d multiplexed busses for I2C %s %s\n",
>  		 num, data->chip->muxtype == pca954x_ismux
>  				? "mux" : "switch", client->name);
>
Greg Kroah-Hartman March 13, 2019, 3:20 p.m. UTC | #2
On Wed, Mar 13, 2019 at 07:04:06AM +0000, Peter Rosin wrote:
> Hi Greg,
> 
> I was wondering if you think the below ABI addition looks sane to you?

I am not the i2c maintainer :)

> Or, should I ask someone else for a tag?

It's the middle of the merge window.  None of us can do much other than
focus on that until 5.1-rc1 is out.

thanks,

greg k-h
Wolfram Sang March 13, 2019, 4:36 p.m. UTC | #3
Hi Greg,

> > I was wondering if you think the below ABI addition looks sane to you?
> I am not the i2c maintainer :)

Peter is the i2c-mux maintainer, so I trust him very much on the I2C
side of things. We just wondered if you'd notice a general flaw when
exposing such an interface to userspace.

> > Or, should I ask someone else for a tag?
> 
> It's the middle of the merge window.  None of us can do much other than
> focus on that until 5.1-rc1 is out.

Sure, thanks anyway for the response.

Regards,

   Wolfram
Greg Kroah-Hartman March 13, 2019, 9:14 p.m. UTC | #4
On Wed, Mar 13, 2019 at 05:36:10PM +0100, Wolfram Sang wrote:
> Hi Greg,
> 
> > > I was wondering if you think the below ABI addition looks sane to you?
> > I am not the i2c maintainer :)
> 
> Peter is the i2c-mux maintainer, so I trust him very much on the I2C
> side of things. We just wondered if you'd notice a general flaw when
> exposing such an interface to userspace.

Ah, I see.  No, looks fine to me, it's a single value, well documented,
should be just fine.

thanks,

greg k-h

Patch
diff mbox series

diff --git a/Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x b/Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x
new file mode 100644
index 000000000000..0b0de8cd0d13
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x
@@ -0,0 +1,20 @@ 
+What:		/sys/bus/i2c/.../idle_state
+Date:		January 2019
+KernelVersion:	5.2
+Contact:	Robert Shearman <robert.shearman@att.com>
+Description:
+		Value that exists only for mux devices that can be
+		written to control the behaviour of the multiplexer on
+		idle. Possible values:
+		-2 - disconnect on idle, i.e. deselect the last used
+		     channel, which is useful when there is a device
+		     with an address that conflicts with another
+		     device on another mux on the same parent bus.
+		-1 - leave the mux as-is, which is the most optimal
+		     setting in terms of I2C operations and is the
+		     default mode.
+		0..<nchans> - set the mux to a predetermined channel,
+		     which is useful if there is one channel that is
+		     used almost always, and you want to reduce the
+		     latency for normal operations after rare
+		     transactions on other channels
diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index e32fef560684..923aa3a5a3dc 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -49,6 +49,7 @@ 
 #include <linux/pm.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <dt-bindings/mux/mux.h>
 
 #define PCA954X_MAX_NCHANS 8
 
@@ -84,7 +85,9 @@  struct pca954x {
 	const struct chip_desc *chip;
 
 	u8 last_chan;		/* last register value */
-	u8 deselect;
+	/* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
+	s8 idle_state;
+
 	struct i2c_client *client;
 
 	struct irq_domain *irq;
@@ -253,15 +256,71 @@  static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 {
 	struct pca954x *data = i2c_mux_priv(muxc);
 	struct i2c_client *client = data->client;
+	s8 idle_state;
+
+	idle_state = READ_ONCE(data->idle_state);
+	if (idle_state >= 0)
+		/* Set the mux back to a predetermined channel */
+		return pca954x_select_chan(muxc, idle_state);
+
+	if (idle_state == MUX_IDLE_DISCONNECT) {
+		/* Deselect active channel */
+		data->last_chan = 0;
+		return pca954x_reg_write(muxc->parent, client,
+					 data->last_chan);
+	}
 
-	if (!(data->deselect & (1 << chan)))
-		return 0;
+	/* otherwise leave as-is */
 
-	/* Deselect active channel */
-	data->last_chan = 0;
-	return pca954x_reg_write(muxc->parent, client, data->last_chan);
+	return 0;
+}
+
+static ssize_t idle_state_show(struct device *dev,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
+	struct pca954x *data = i2c_mux_priv(muxc);
+
+	return sprintf(buf, "%d\n", READ_ONCE(data->idle_state));
+}
+
+static ssize_t idle_state_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
+	struct pca954x *data = i2c_mux_priv(muxc);
+	int val;
+	int ret;
+
+	ret = kstrtoint(buf, 0, &val);
+	if (ret < 0)
+		return ret;
+
+	if (val != MUX_IDLE_AS_IS && val != MUX_IDLE_DISCONNECT &&
+	    (val < 0 || val >= data->chip->nchans))
+		return -EINVAL;
+
+	i2c_lock_bus(muxc->parent, I2C_LOCK_SEGMENT);
+
+	WRITE_ONCE(data->idle_state, val);
+	/*
+	 * Set the mux into a state consistent with the new
+	 * idle_state.
+	 */
+	if (data->last_chan || val != MUX_IDLE_DISCONNECT)
+		ret = pca954x_deselect_mux(muxc, 0);
+
+	i2c_unlock_bus(muxc->parent, I2C_LOCK_SEGMENT);
+
+	return ret < 0 ? ret : count;
 }
 
+static DEVICE_ATTR_RW(idle_state);
+
 static irqreturn_t pca954x_irq_handler(int irq, void *dev_id)
 {
 	struct pca954x *data = dev_id;
@@ -328,8 +387,11 @@  static int pca954x_irq_setup(struct i2c_mux_core *muxc)
 static void pca954x_cleanup(struct i2c_mux_core *muxc)
 {
 	struct pca954x *data = i2c_mux_priv(muxc);
+	struct i2c_client *client = data->client;
 	int c, irq;
 
+	device_remove_file(&client->dev, &dev_attr_idle_state);
+
 	if (data->irq) {
 		for (c = 0; c < data->chip->nchans; c++) {
 			irq = irq_find_mapping(data->irq, c);
@@ -410,9 +472,12 @@  static int pca954x_probe(struct i2c_client *client,
 	}
 
 	data->last_chan = 0;		   /* force the first selection */
+	data->idle_state = MUX_IDLE_AS_IS;
 
 	idle_disconnect_dt = np &&
 		of_property_read_bool(np, "i2c-mux-idle-disconnect");
+	if (idle_disconnect_dt)
+		data->idle_state = MUX_IDLE_DISCONNECT;
 
 	ret = pca954x_irq_setup(muxc);
 	if (ret)
@@ -420,8 +485,6 @@  static int pca954x_probe(struct i2c_client *client,
 
 	/* Now create an adapter for each channel */
 	for (num = 0; num < data->chip->nchans; num++) {
-		data->deselect |= idle_disconnect_dt << num;
-
 		ret = i2c_mux_add_adapter(muxc, 0, num, 0);
 		if (ret)
 			goto fail_cleanup;
@@ -436,6 +499,12 @@  static int pca954x_probe(struct i2c_client *client,
 			goto fail_cleanup;
 	}
 
+	/*
+	 * The attr probably isn't going to be needed in most cases,
+	 * so don't fail completely on error.
+	 */
+	device_create_file(dev, &dev_attr_idle_state);
+
 	dev_info(dev, "registered %d multiplexed busses for I2C %s %s\n",
 		 num, data->chip->muxtype == pca954x_ismux
 				? "mux" : "switch", client->name);