[PATCH 2/2] i2c: add ACPI support for I2C mux ports

[Dustin Byford]

Although I2C mux devices are easily enumerated using ACPI (_HID/_CID or
device property compatible string match) enumerating I2C client devices
connected through a I2C mux device requires a little extra work.

This change implements a method for describing an I2C device hierarchy that
includes mux devices by using an ACPI Device() for each mux channel along
with an _ADR to set the channel number for the device.  See
Documentation/acpi/i2c-muxes.txt for a simple example.

Signed-off-by: Dustin Byford <dustin@xxxxxxxxxxxxxxxxxxx>
---
 Documentation/acpi/i2c-muxes.txt | 58 ++++++++++++++++++++++++++++++++++++++++
 drivers/i2c/i2c-core.c           | 18 +++++++++++--
 drivers/i2c/i2c-mux.c            |  8 ++++++
 3 files changed, 82 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/acpi/i2c-muxes.txt

diff --git a/Documentation/acpi/i2c-muxes.txt b/Documentation/acpi/i2c-muxes.txt
new file mode 100644
index 0000000..efdcf0d
--- /dev/null
+++ b/Documentation/acpi/i2c-muxes.txt
@@ -0,0 +1,58 @@
+ACPI I2C Muxes
+--------------
+
+Describing an I2C device hierarchy that includes I2C muxes requires an ACPI
+Device() scope per mux channel.
+
+Consider this topology:
+
++------+   +------+
+| SMB1 |-->| MUX0 |--CH00--> i2c client A (0x50)
+|      |   | 0x70 |--CH01--> i2c client B (0x50)
++------+   +------+
+
+which corresponds to the following ASL:
+
+Device(SMB1)
+{
+    Name (_HID, ...)
+    Device(MUX0)
+    {
+        Name (_HID, ...)
+        Name (_CRS, ResourceTemplate () {
+            I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
+                          AddressingMode7Bit, "^SMB1", 0x00,
+                          ResourceConsumer,,)
+        }
+
+        Device(CH00)
+        {
+            Name (_ADR, 0)
+
+            Device(CLIA)
+            {
+                Name (_HID, ...)
+                Name (_CRS, ResourceTemplate () {
+                    I2cSerialBus (0x50, ControllerInitiated, I2C_SPEED,
+                                  AddressingMode7Bit, "^CH00", 0x00,
+                                  ResourceConsumer,,)
+                }
+            }
+        }
+
+        Device(CH01)
+        {
+            Name (_ADR, 1)
+
+            Device(CLIB)
+            {
+                Name (_HID, ...)
+                Name (_CRS, ResourceTemplate () {
+                    I2cSerialBus (0x50, ControllerInitiated, I2C_SPEED,
+                                  AddressingMode7Bit, "^CH01", 0x00,
+                                  ResourceConsumer,,)
+                }
+            }
+        }
+    }
+}
diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 3a4c54e..a2de010 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -156,7 +156,10 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
 	info.fwnode = acpi_fwnode_handle(adev);
 
 	memset(&lookup, 0, sizeof(lookup));
-	lookup.adapter_handle = ACPI_HANDLE(adapter->dev.parent);
+	if (i2c_parent_is_i2c_adapter(adapter))
+		lookup.adapter_handle = ACPI_HANDLE(&adapter->dev);
+	else
+		lookup.adapter_handle = ACPI_HANDLE(adapter->dev.parent);
 	lookup.device_handle = handle;
 	lookup.info = &info;
 
@@ -210,9 +213,20 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
  */
 static void acpi_i2c_register_devices(struct i2c_adapter *adap)
 {
+	struct device *dev;
 	acpi_status status;
 
-	if (!adap->dev.parent || !has_acpi_companion(adap->dev.parent))
+	/*
+	 * Typically we look at the ACPI device's parent for an ACPI companion.
+	 * However, in the case of an I2C-connected I2C mux, the "virtual" I2C
+	 * adapter allocated for the mux channel has that association.
+	 */
+	if (i2c_parent_is_i2c_adapter(adap))
+		dev = &adap->dev;
+	else
+		dev = adap->dev.parent;
+
+	if (!has_acpi_companion(dev))
 		return;
 
 	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 2ba7c0f..00fc5b1 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,
 		}
 	}
 
+	/*
+	 * Associate the mux channel with an 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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