diff options
| author | Bartosz Golaszewski <bgolaszewski@baylibre.com> | 2016-09-26 11:54:15 +0200 |
|---|---|---|
| committer | Wolfram Sang <wsa@the-dreams.de> | 2016-10-11 23:17:08 +0200 |
| commit | 74f47f07e53daeca1d16812fa7c9bf3145bd8216 (patch) | |
| tree | 2d3e391673d544148dc5956ee85fb175cb43d4ce | |
| parent | de34f4da7f62ff59ac6e1ef320b0fcfa3296fce3 (diff) | |
| download | linux-74f47f07e53daeca1d16812fa7c9bf3145bd8216.tar.gz | |
gpio: pca953x: add a comment explaining the need for a lockdep subclass
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 <bgolaszewski@baylibre.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
| -rw-r--r-- | drivers/gpio/gpio-pca953x.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c index 45c8817d068c..e422568e14ad 100644 --- a/drivers/gpio/gpio-pca953x.c +++ b/drivers/gpio/gpio-pca953x.c @@ -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)); |