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authorBartosz Golaszewski <bgolaszewski@baylibre.com>2016-09-26 11:54:15 +0200
committerWolfram Sang <wsa@the-dreams.de>2016-10-11 23:17:08 +0200
commit74f47f07e53daeca1d16812fa7c9bf3145bd8216 (patch)
tree2d3e391673d544148dc5956ee85fb175cb43d4ce
parentde34f4da7f62ff59ac6e1ef320b0fcfa3296fce3 (diff)
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.c16
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));