[PATCH 1/2] i2c: core: Allow the driver to override the default i2c_bus match behavior

[Hans de Goede <hdegoede@redhat.com>]

Some ACPI devices report multiple ids for a single i2c_client, while not
really implementing the hw-interface asociated with some of these ids.

For some of these devices calling probe and having probe fail with
-ENODEV is a problem in itself as this causes the device to be
powered-up and down again (causes its PS0 and PS3 ACPI methods to be
executed) which puts some devices in an unusable state.

This commit adds a match callback to i2c_driver, allowing drivers to
override the default i2c_bus match behavior and tell the core they
are not the right driver for the device, avoiding i2c_bus_type.probe
getting called, avoiding the undesirable power up / down cycle.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/i2c/i2c-core-base.c | 12 +++++++++---
 include/linux/i2c.h         |  6 ++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index c89dac7fd2e7..2c6702f2347b 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -98,8 +98,16 @@ EXPORT_SYMBOL_GPL(i2c_match_id);
 static int i2c_device_match(struct device *dev, struct device_driver *drv)
 {
 	struct i2c_client	*client = i2c_verify_client(dev);
-	struct i2c_driver	*driver;
+	struct i2c_driver	*driver = to_i2c_driver(drv);
+	int ret;
 
+	if (driver->match && client) {
+		ret = driver->match(client);
+		if (ret < 0)
+			return 0;
+		if (ret > 0)
+			return 1;
+	}
 
 	/* Attempt an OF style match */
 	if (i2c_of_match_device(drv->of_match_table, client))
@@ -109,8 +117,6 @@ static int i2c_device_match(struct device *dev, struct device_driver *drv)
 	if (acpi_driver_match_device(dev, drv))
 		return 1;
 
-	driver = to_i2c_driver(drv);
-
 	/* Finally an I2C match */
 	if (i2c_match_id(driver->id_table, client))
 		return 1;
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 00ca5b86a753..670577c82bc3 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -139,6 +139,9 @@ enum i2c_alert_protocol {
  * struct i2c_driver - represent an I2C device driver
  * @class: What kind of i2c device we instantiate (for detect)
  * @attach_adapter: Callback for bus addition (deprecated)
+ * @match: Allows the driver to override the default i2c_bus match behavior
+ *         return < 0 to fail the match, > 0 to force a match, 0 to fallback
+ *         to default id matching
  * @probe: Callback for device binding - soon to be deprecated
  * @probe_new: New callback for device binding
  * @remove: Callback for device unbinding
@@ -180,6 +183,9 @@ struct i2c_driver {
 	 */
 	int (*attach_adapter)(struct i2c_adapter *) __deprecated;
 
+	/* Set this to override standard i2c_bus match behavior */
+	int (*match)(struct i2c_client *);
+
 	/* Standard driver model interfaces */
 	int (*probe)(struct i2c_client *, const struct i2c_device_id *);
 	int (*remove)(struct i2c_client *);
-- 
2.13.0