gpio: pca953x: add a comment explaining the need for a lockdep subclass (74f47f07) · Commits · 戴 / test

This is a follow-up to commit ("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:

Bartosz Golaszewski <bgolaszewski@baylibre.com> Acked-by:

Linus Walleij <linus.walleij@linaro.org> Signed-off-by:

Wolfram Sang <wsa@the-dreams.de>

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));

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