This is a follow-up to commit 559b46990e76 ("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 <[email protected]> --- drivers/gpio/gpio-pca953x.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c index 018f39c..f306909 100644 --- a/drivers/gpio/gpio-pca953x.c +++ b/drivers/gpio/gpio-pca953x.c @@ -786,6 +786,22 @@ static int pca953x_probe(struct i2c_client *client, chip->chip_type = PCA_CHIP_TYPE(chip->driver_data); 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)); -- 2.7.4
