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 <dus...@cumulusnetworks.com>
---
Documentation/acpi/i2c-muxes.txt | 58 ++++++++++++++++++++++++++++++++++++++++
drivers/i2c/i2c-core.c | 15 +++++++++--
drivers/i2c/i2c-mux.c | 8 ++++++
include/linux/acpi.h | 6 +++++
4 files changed, 85 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..9fcc4f0
--- /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 579b99d..af0811c 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -156,7 +156,7 @@ 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);
+ lookup.adapter_handle = ACPI_HANDLE(&adapter->dev);
lookup.device_handle = handle;
lookup.info = &info;
@@ -212,7 +212,7 @@ static void acpi_i2c_register_devices(struct i2c_adapter
*adap)
{
acpi_status status;
- if (!adap->dev.parent || !has_acpi_companion(adap->dev.parent))
+ if (!has_acpi_companion(&adap->dev))
return;
status = acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
@@ -1667,6 +1667,17 @@ int i2c_add_adapter(struct i2c_adapter *adapter)
struct device *dev = &adapter->dev;
int id;
+ /*
+ * By default, associate I2C adapters with their parent device's ACPI
+ * node.
+ */
+ if (!has_acpi_companion(dev)) {
+ struct acpi_device *adev = ACPI_COMPANION(dev->parent);
+
+ if (adev)
+ ACPI_COMPANION_SET(dev, adev);
+ }
+
if (dev->of_node) {
id = of_alias_get_id(dev->of_node, "i2c");
if (id >= 0) {
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);
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 51a96a8..66564f8 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -505,6 +505,12 @@ static inline bool has_acpi_companion(struct device *dev)
return false;
}
+static inline void acpi_preset_companion(struct device *dev,
+ struct acpi_device *parent, u64 addr)
+{
+ return;
+}
+
static inline const char *acpi_dev_name(struct acpi_device *adev)
{
return NULL;
--
2.1.4
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