[v4,0/3] Extend device_get_match_data() to struct bus_type

This patch series extend device_get_match_data() to struct bus_type,
so that buses like I2C can get matched data.

v3->v4:
 * Documented corner case for device_get_match_data()
 * Dropped struct i2c_driver parameter from i2c_get_match_data_helper()
 * Split I2C sysfs handling in seperate patch(patch#3)
 * Added space after of_device_id for i2c_of_match_device_sysfs()
 * Added const parameter for struct i2c_client, to prevent overriding it's
   pointer.
 * Moved declaration from public i2c.h->i2c-core.h
v2->v3:
 * Added Rb tag from Andy for patch#1.
 * Extended to support i2c_of_match_device() as suggested by Andy.
 * Changed i2c_of_match_device_sysfs() as non-static function as it is
   needed for i2c_device_get_match_data().
 * Added a TODO comment to use i2c_verify_client() when it accepts const
   pointer.
 * Added multiple returns to make code path for device_get_match_data()
   faster in i2c_get_match_data().
RFC v1->v2:
 * Replaced "Signed-off-by"->"Suggested-by" tag for Dmitry.
 * Documented device_get_match_data().
 * Added multiple returns to make code path for generic fwnode-based
   lookup faster.
 * Fixed build warnings reported by kernel test robot <lkp@intel.com>
 * Added const qualifier to return type and parameter struct i2c_driver
   in i2c_get_match_data_helper().
 * Added const qualifier to struct i2c_driver in i2c_get_match_data()
 * Dropped driver variable from i2c_device_get_match_data()
 * Replaced to_i2c_client with logic for assigning verify_client as it
   returns non const pointer.

Biju Das (3):
  drivers: fwnode: Extend device_get_match_data() to struct bus_type
  i2c: Add i2c_device_get_match_data() callback
  i2c: Extend i2c_device_get_match_data() to support i2c sysfs

 drivers/base/property.c     | 27 ++++++++++++++++++++-
 drivers/i2c/i2c-core-base.c | 48 ++++++++++++++++++++++++++++++-------
 drivers/i2c/i2c-core-of.c   |  5 ++--
 drivers/i2c/i2c-core.h      |  9 +++++++
 include/linux/device/bus.h  |  3 +++
 5 files changed, 81 insertions(+), 11 deletions(-)

On Wed, Aug 02, 2023 at 12:23:16PM +0100, Biju Das wrote:
> Add i2c_device_get_match_data() callback to struct bus_type().
> 
> While at it, introduced i2c_get_match_data_helper() to avoid code
> duplication with i2c_get_match_data().

...

> +static const void *i2c_get_match_data_helper(const struct i2c_client *client)
>  {
> -	struct i2c_driver *driver = to_i2c_driver(client->dev.driver);
> +	const struct i2c_driver *driver = to_i2c_driver(client->dev.driver);
>  	const struct i2c_device_id *match;
> +
> +	match = i2c_match_id(driver->id_table, client);
> +	if (!match)
> +		return NULL;
> +
> +	return (const void *)match->driver_data;
> +}

Yes, perfect!

...

> +static const void *i2c_device_get_match_data(const struct device *dev)
> +{
> +	/* TODO: use i2c_verify_client() when it accepts const pointer */
> +	const struct i2c_client *client = (dev->type == &i2c_client_type) ?
> +					  to_i2c_client(dev) : NULL;
> +
> +	if (!client || !dev->driver)
> +		return NULL;
> +
> +	return i2c_get_match_data_helper(client);


I believe below looks better from readability and maintenance perspectives.

	const struct i2c_client *client;

	/* ...comment as in Dmitry's reply in v3 thread on why we need this check... */
	if (!dev->driver)
		return NULL;

	/* TODO: use i2c_verify_client() when it accepts const pointer */
	client = (dev->type == &i2c_client_type) ? to_i2c_client(dev) : NULL;
	if (!client)
		return NULL;

> +	return i2c_get_match_data_helper(client);
> +}