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Commit 74f47f07 authored by Bartosz Golaszewski's avatar Bartosz Golaszewski Committed by Wolfram Sang
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gpio: pca953x: add a comment explaining the need for a lockdep subclass 



This is a follow-up to commit 559b4699 ("gpio: pca953x: fix an
incorrect lockdep warning"). The reason for calling
lockdep_set_subclass() in pca953x_probe() is not explained in
the code.

Add a comment describing the problem, partial solution and required
future extensions.

Signed-off-by: default avatarBartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: default avatarWolfram Sang <wsa@the-dreams.de>
parent de34f4da

drivers/gpio/gpio-pca953x.c

+16 −0
Original line number Diff line number Diff line
@@ -794,6 +794,22 @@ static int pca953x_probe(struct i2c_client *client, 
	}



	mutex_init(&chip->i2c_lock);

	/*

	 * In case we have an i2c-mux controlled by a GPIO provided by an

	 * expander using the same driver higher on the device tree, read the

	 * i2c adapter nesting depth and use the retrieved value as lockdep

	 * subclass for chip->i2c_lock.

	 *

	 * REVISIT: This solution is not complete. It protects us from lockdep

	 * false positives when the expander controlling the i2c-mux is on

	 * a different level on the device tree, but not when it's on the same

	 * level on a different branch (in which case the subclass number

	 * would be the same).

	 *

	 * TODO: Once a correct solution is developed, a similar fix should be

	 * applied to all other i2c-controlled GPIO expanders (and potentially

	 * regmap-i2c).

	 */

	lockdep_set_subclass(&chip->i2c_lock,

			     i2c_adapter_depth(client->adapter));