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[RFC PATCH 0/1] i2c: scan ACPI enumerated I2C mux channels

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  [RFC PATCH 0/1] i2c: scan ACPI enumerated I2C mux channels Dustin Byford <dustin@cumulusnetworks.com> - 2015-08-14 02:00 +0200
    [RFC PATCH 1/1] i2c: acpi: scan ACPI enumerated I2C mux channels Dustin Byford <dustin@cumulusnetworks.com> - 2015-08-14 02:00 +0200
    [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels Dustin Byford <dustin@cumulusnetworks.com> - 2015-08-14 21:40 +0200
      Re: [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels Wolfram Sang <wsa@the-dreams.de> - 2015-08-15 22:30 +0200
      Re: [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels Mika Westerberg <mika.westerberg@linux.intel.com> - 2015-08-17 14:10 +0200
        Re: [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels Dustin Byford <dustin@cumulusnetworks.com> - 2015-08-17 21:10 +0200

#1207249 — [RFC PATCH 0/1] i2c: scan ACPI enumerated I2C mux channels

I would like to add support for scanning I2C devices connected to ACPI
OF compatible muxes described in ASL like this:

Device (MUX0)
{
    Name (_ADR, 0x70)
    Name (_HID, "PRP0001")
    Name (_CRS, ResourceTemplate()
    {
        I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
                      AddressingMode7Bit, "^^SMB2", 0x00,
                      ResourceConsumer,,)
    })
    Name (_DSD, Package ()
    {
        ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
        Package () {
            Package (2) { "compatible", "nxp,pca9548" },
        }
    })

    // MUX channels
    Device (CH00) { Name (_ADR, 0x0) }
}

Scope(MUX0.CH00)
{
    Device (TMP0) {
        /* Temp sensor ASL, for example. */
    }
}

It seems like a reasonable way to describe a common I2C component and
kernel support is almost there.

I had to:

1) Find and set an ACPI companion for the "virtual" I2C adapters created
   for each mux channel.

2) Make sure to scan adap.dev when registering devices under each mux
   channel.

At first, I was confused about why adap.dev->parent is used in
acpi_i2c_register_devices().  I found b34bb1ee from 4/2013 (ACPI / I2C:
Use parent's ACPI_HANDLE()), which offers an explanation.

This patch works well, but I'm not sure about the code to just fall back
to using adap.dev when adap.dev->parent doesn't have an ACPI companion.
Is there a more explicit check I can make to determine if the adapter
represents a mux channel?

Any feedback would be welcome.  Thanks,

   --Dustin

Dustin Byford (1):
  i2c: acpi: scan ACPI enumerated I2C mux channels

 drivers/i2c/i2c-core.c | 10 ++++++++++
 drivers/i2c/i2c-mux.c  |  8 ++++++++
 2 files changed, 18 insertions(+)

-- 
2.1.4

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#1207251 — [RFC PATCH 1/1] i2c: acpi: scan ACPI enumerated I2C mux channels

Set an ACPI companion for I2C mux channels enumerated through ACPI and
ensure they are scanned for devices.

Signed-off-by: Dustin Byford <dustin@cumulusnetworks.com>
---
 drivers/i2c/i2c-core.c | 10 ++++++++++
 drivers/i2c/i2c-mux.c  |  8 ++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index c83e4d1..23cc8e9 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -171,8 +171,18 @@ static void acpi_i2c_register_devices(struct i2c_adapter *adap)
 	if (!adap->dev.parent)
 		return;
 
+	/*
+	 * Determine where to start walking the ACPI namespace.  The common
+	 * case is to start at the adapter's parent device.  However, in
+	 * the case of a "virtual" I2C adapter created to represent a mux
+	 * channel the parent dev (pointing to the mux device) does not
+	 * have an ACPI handle.  Walk starting at the adapter instead.
+	 */
 	handle = ACPI_HANDLE(adap->dev.parent);
 	if (!handle)
+		handle = ACPI_HANDLE(&adap->dev);
+
+	if (!handle)
 		return;
 
 	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, 1,
diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 2ba7c0f..2731b99 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -25,6 +25,7 @@
 #include <linux/i2c.h>
 #include <linux/i2c-mux.h>
 #include <linux/of.h>
+#include <linux/acpi.h>
 
 /* multiplexer per channel data */
 struct i2c_mux_priv {
@@ -173,6 +174,13 @@ struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
 		}
 	}
 
+	/*
+	 * Now try to populate the mux adapter's ACPI node.
+	 */
+	if (has_acpi_companion(mux_dev))
+		acpi_preset_companion(&priv->adap.dev, ACPI_COMPANION(mux_dev),
+				      chan_id);
+
 	if (force_nr) {
 		priv->adap.nr = force_nr;
 		ret = i2c_add_numbered_adapter(&priv->adap);
-- 
2.1.4

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#1207883 — [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels

(v2 corrects cc: list)

I would like to add support for scanning I2C devices connected to ACPI
OF compatible muxes described in ASL like this:

Device (MUX0)
{
    Name (_ADR, 0x70)
    Name (_HID, "PRP0001")
    Name (_CRS, ResourceTemplate()
    {
        I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
                      AddressingMode7Bit, "^^SMB2", 0x00,
                      ResourceConsumer,,)
    })
    Name (_DSD, Package ()
    {
        ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
        Package () {
            Package (2) { "compatible", "nxp,pca9548" },
        }
    })

    // MUX channels
    Device (CH00) { Name (_ADR, 0x0) }
}

Scope(MUX0.CH00)
{
    Device (TMP0) {
        /* Temp sensor ASL, for example. */
    }
}

It seems like a reasonable way to describe a common I2C component and
kernel support is almost there.

I had to:

1) Find and set an ACPI companion for the "virtual" I2C adapters created
   for each mux channel.

2) Make sure to scan adap.dev when registering devices under each mux
   channel.

At first, I was confused about why adap.dev->parent is used in
acpi_i2c_register_devices().  I found b34bb1ee from 4/2013 (ACPI / I2C:
Use parent's ACPI_HANDLE()), which offers an explanation.

This patch works well, but I'm not sure about the code to just fall back
to using adap.dev when adap.dev->parent doesn't have an ACPI companion.
Is there a more explicit check I can make to determine if the adapter
represents a mux channel?

Any feedback would be welcome.  Thanks,

   --Dustin

Dustin Byford (1):
  i2c: acpi: scan ACPI enumerated I2C mux channels

 drivers/i2c/i2c-core.c | 10 ++++++++++
 drivers/i2c/i2c-mux.c  |  8 ++++++++
 2 files changed, 18 insertions(+)

-- 
2.1.4

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#1208157 — Re: [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels

On Fri, Aug 14, 2015 at 12:31:32PM -0700, Dustin Byford wrote:
> 
> (v2 corrects cc: list)

And adding Mika to the cc-list who is our I2C and ACPI expert.
Mika can you have a look at this and the other patches Dustin sent
recently to the i2c list?

Thanks,

   Wolfram

> 
> I would like to add support for scanning I2C devices connected to ACPI
> OF compatible muxes described in ASL like this:
> 
> Device (MUX0)
> {
>     Name (_ADR, 0x70)
>     Name (_HID, "PRP0001")
>     Name (_CRS, ResourceTemplate()
>     {
>         I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
>                       AddressingMode7Bit, "^^SMB2", 0x00,
>                       ResourceConsumer,,)
>     })
>     Name (_DSD, Package ()
>     {
>         ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>         Package () {
>             Package (2) { "compatible", "nxp,pca9548" },
>         }
>     })
> 
>     // MUX channels
>     Device (CH00) { Name (_ADR, 0x0) }
> }
> 
> Scope(MUX0.CH00)
> {
>     Device (TMP0) {
>         /* Temp sensor ASL, for example. */
>     }
> }
> 
> It seems like a reasonable way to describe a common I2C component and
> kernel support is almost there.
> 
> I had to:
> 
> 1) Find and set an ACPI companion for the "virtual" I2C adapters created
>    for each mux channel.
> 
> 2) Make sure to scan adap.dev when registering devices under each mux
>    channel.
> 
> At first, I was confused about why adap.dev->parent is used in
> acpi_i2c_register_devices().  I found b34bb1ee from 4/2013 (ACPI / I2C:
> Use parent's ACPI_HANDLE()), which offers an explanation.
> 
> This patch works well, but I'm not sure about the code to just fall back
> to using adap.dev when adap.dev->parent doesn't have an ACPI companion.
> Is there a more explicit check I can make to determine if the adapter
> represents a mux channel?
> 
> Any feedback would be welcome.  Thanks,
> 
>    --Dustin
> 
> Dustin Byford (1):
>   i2c: acpi: scan ACPI enumerated I2C mux channels
> 
>  drivers/i2c/i2c-core.c | 10 ++++++++++
>  drivers/i2c/i2c-mux.c  |  8 ++++++++
>  2 files changed, 18 insertions(+)
> 
> -- 
> 2.1.4
> 
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#1208562 — Re: [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels

On Fri, Aug 14, 2015 at 12:31:32PM -0700, Dustin Byford wrote:
> 
> (v2 corrects cc: list)
> 
> I would like to add support for scanning I2C devices connected to ACPI
> OF compatible muxes described in ASL like this:
> 
> Device (MUX0)
> {
>     Name (_ADR, 0x70)
>     Name (_HID, "PRP0001")
>     Name (_CRS, ResourceTemplate()
>     {
>         I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
>                       AddressingMode7Bit, "^^SMB2", 0x00,
>                       ResourceConsumer,,)
>     })
>     Name (_DSD, Package ()
>     {
>         ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>         Package () {
>             Package (2) { "compatible", "nxp,pca9548" },
>         }

Nice, you are using _DSD :-)

>     })
> 
>     // MUX channels
>     Device (CH00) { Name (_ADR, 0x0) }
> }
> 
> Scope(MUX0.CH00)
> {
>     Device (TMP0) {
>         /* Temp sensor ASL, for example. */
>     }
> }
> 
> It seems like a reasonable way to describe a common I2C component and
> kernel support is almost there.
> 
> I had to:
> 
> 1) Find and set an ACPI companion for the "virtual" I2C adapters created
>    for each mux channel.
> 
> 2) Make sure to scan adap.dev when registering devices under each mux
>    channel.
> 
> At first, I was confused about why adap.dev->parent is used in
> acpi_i2c_register_devices().  I found b34bb1ee from 4/2013 (ACPI / I2C:
> Use parent's ACPI_HANDLE()), which offers an explanation.
> 
> This patch works well, but I'm not sure about the code to just fall back
> to using adap.dev when adap.dev->parent doesn't have an ACPI companion.
> Is there a more explicit check I can make to determine if the adapter
> represents a mux channel?

I think the current code in I2C core is not actually doing the right
thing according the ACPI spec at least. To my understanding you can have
device with I2cSerialBus resource _anywhere_ in the namespace, not just
directly below the host controller. It's the ResourceSource attribute
that tells the corresponding host controller.

I wonder if it helps if we scan the whole namespace for devices with
I2cSerialBus that matches the just registered adapter? Something like
the patch below.

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index c83e4d13cfc5..2a309d27421a 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -94,27 +94,40 @@ struct gsb_buffer {
 	};
 } __packed;
 
-static int acpi_i2c_add_resource(struct acpi_resource *ares, void *data)
+struct acpi_i2c_lookup {
+	struct i2c_board_info *info;
+	acpi_handle adapter_handle;
+	acpi_handle device_handle;
+};
+
+static int acpi_i2c_find_address(struct acpi_resource *ares, void *data)
 {
-	struct i2c_board_info *info = data;
+	struct acpi_i2c_lookup *lookup = data;
+	struct i2c_board_info *info = lookup->info;
+	struct acpi_resource_i2c_serialbus *sb;
+	acpi_handle adapter_handle;
+	acpi_status status;
 
-	if (ares->type == ACPI_RESOURCE_TYPE_SERIAL_BUS) {
-		struct acpi_resource_i2c_serialbus *sb;
+	if (info->addr || ares->type != ACPI_RESOURCE_TYPE_SERIAL_BUS)
+		return 1;
 
-		sb = &ares->data.i2c_serial_bus;
-		if (!info->addr && sb->type == ACPI_RESOURCE_SERIAL_TYPE_I2C) {
-			info->addr = sb->slave_address;
-			if (sb->access_mode == ACPI_I2C_10BIT_MODE)
-				info->flags |= I2C_CLIENT_TEN;
-		}
-	} else if (!info->irq) {
-		struct resource r;
+	sb = &ares->data.i2c_serial_bus;
+	if (sb->type != ACPI_RESOURCE_SERIAL_TYPE_I2C)
+		return 1;
 
-		if (acpi_dev_resource_interrupt(ares, 0, &r))
-			info->irq = r.start;
+	/*
+	 * Extract the ResourceSource and make sure that the handle matches
+	 * with the I2C adapter handle.
+	 */
+	status = acpi_get_handle(lookup->device_handle,
+				 sb->resource_source.string_ptr,
+				 &adapter_handle);
+	if (ACPI_SUCCESS(status) && adapter_handle == lookup->adapter_handle) {
+		info->addr = sb->slave_address;
+		if (sb->access_mode == ACPI_I2C_10BIT_MODE)
+			info->flags |= I2C_CLIENT_TEN;
 	}
 
-	/* Tell the ACPI core to skip this resource */
 	return 1;
 }
 
@@ -123,6 +136,8 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
 {
 	struct i2c_adapter *adapter = data;
 	struct list_head resource_list;
+	struct acpi_i2c_lookup lookup;
+	struct resource_entry *entry;
 	struct i2c_board_info info;
 	struct acpi_device *adev;
 	int ret;
@@ -135,14 +150,37 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
 	memset(&info, 0, sizeof(info));
 	info.fwnode = acpi_fwnode_handle(adev);
 
+	memset(&lookup, 0, sizeof(lookup));
+	lookup.adapter_handle = ACPI_HANDLE(adapter->dev.parent);
+	lookup.device_handle = handle;
+	lookup.info = &info;
+
+	/*
+	 * Look up for I2cSerialBus resource with ResourceSource that
+	 * matches with this adapter.
+	 */
 	INIT_LIST_HEAD(&resource_list);
 	ret = acpi_dev_get_resources(adev, &resource_list,
-				     acpi_i2c_add_resource, &info);
+				     acpi_i2c_find_address, &lookup);
 	acpi_dev_free_resource_list(&resource_list);
 
 	if (ret < 0 || !info.addr)
 		return AE_OK;
 
+	/* Then fill IRQ number if any */
+	ret = acpi_dev_get_resources(adev, &resource_list, NULL, NULL);
+	if (ret < 0)
+		return AE_OK;
+
+	resource_list_for_each_entry(entry, &resource_list) {
+		if (resource_type(entry->res) == IORESOURCE_IRQ) {
+			info.irq = entry->res->start;
+			break;
+		}
+	}
+
+	acpi_dev_free_resource_list(&resource_list);
+
 	adev->power.flags.ignore_parent = true;
 	strlcpy(info.type, dev_name(&adev->dev), sizeof(info.type));
 	if (!i2c_new_device(adapter, &info)) {
@@ -155,6 +193,8 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
 	return AE_OK;
 }
 
+#define ACPI_I2C_MAX_SCAN_DEPTH 32
+
 /**
  * acpi_i2c_register_devices - enumerate I2C slave devices behind adapter
  * @adap: pointer to adapter
@@ -165,17 +205,13 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
  */
 static void acpi_i2c_register_devices(struct i2c_adapter *adap)
 {
-	acpi_handle handle;
 	acpi_status status;
 
-	if (!adap->dev.parent)
-		return;
-
-	handle = ACPI_HANDLE(adap->dev.parent);
-	if (!handle)
+	if (!adap->dev.parent || !has_acpi_companion(adap->dev.parent))
 		return;
 
-	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, 1,
+	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
+				     ACPI_I2C_MAX_SCAN_DEPTH,
 				     acpi_i2c_add_device, NULL,
 				     adap, NULL);
 	if (ACPI_FAILURE(status))
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#1208797 — Re: [RFC v2 0/1] i2c: acpi: scan ACPI enumerated I2C mux channels

Hi Mika,

Thanks for taking a look.

On Mon Aug 17 15:03, Mika Westerberg wrote:
> On Fri, Aug 14, 2015 at 12:31:32PM -0700, Dustin Byford wrote:

> >     Name (_DSD, Package ()
> >     {
> >         ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> >         Package () {
> >             Package (2) { "compatible", "nxp,pca9548" },
> >         }
> 
> Nice, you are using _DSD :-)

Yes, and I've got some other patches related to that.  I'll keep
sending, but the relative youth of _DSD does bring up a few higher level
issues (for me at least).  One thing at a time though, stay tuned.

> > I had to:
> > 
> > 1) Find and set an ACPI companion for the "virtual" I2C adapters created
> >    for each mux channel.
> > 
> > 2) Make sure to scan adap.dev when registering devices under each mux
> >    channel.

> I think the current code in I2C core is not actually doing the right
> thing according the ACPI spec at least. To my understanding you can have
> device with I2cSerialBus resource _anywhere_ in the namespace, not just
> directly below the host controller. It's the ResourceSource attribute
> that tells the corresponding host controller.

I think you're right.

> I wonder if it helps if we scan the whole namespace for devices with
> I2cSerialBus that matches the just registered adapter? Something like
> the patch below.

Looks reasonable to me.  Let me work with the patch for a bit and see if
I can make it work in my system.

		--Dustin
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