gpio: pca953x: add a comment explaining the need for a lockdep subclass

[cascardo/linux.git] / drivers / gpio / gpio-pca953x.c

diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
index f170c56..e422568 100644 (file)
--- a/drivers/gpio/gpio-pca953x.c
+++ b/drivers/gpio/gpio-pca953x.c
@@ -732,7 +732,7 @@ out:
 static const struct of_device_id pca953x_dt_ids[];
 
 static int pca953x_probe(struct i2c_client *client,
-                                  const struct i2c_device_id *id)
+                                  const struct i2c_device_id *i2c_id)
 {
        struct pca953x_platform_data *pdata;
        struct pca953x_chip *chip;
@@ -773,27 +773,45 @@ static int pca953x_probe(struct i2c_client *client,
        }
        chip->regulator = reg;
 
-       if (id) {
-               chip->driver_data = id->driver_data;
+       if (i2c_id) {
+               chip->driver_data = i2c_id->driver_data;
        } else {
-               const struct acpi_device_id *id;
+               const struct acpi_device_id *acpi_id;
                const struct of_device_id *match;
 
                match = of_match_device(pca953x_dt_ids, &client->dev);
                if (match) {
                        chip->driver_data = (int)(uintptr_t)match->data;
                } else {
-                       id = acpi_match_device(pca953x_acpi_ids, &client->dev);
-                       if (!id) {
+                       acpi_id = acpi_match_device(pca953x_acpi_ids, &client->dev);
+                       if (!acpi_id) {
                                ret = -ENODEV;
                                goto err_exit;
                        }
 
-                       chip->driver_data = id->driver_data;
+                       chip->driver_data = acpi_id->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));
 
        /* initialize cached registers from their original values.
         * we can't share this chip with another i2c master.
@@ -848,7 +866,7 @@ static int pca953x_remove(struct i2c_client *client)
 {
        struct pca953x_platform_data *pdata = dev_get_platdata(&client->dev);
        struct pca953x_chip *chip = i2c_get_clientdata(client);
-       int ret = 0;
+       int ret;
 
        if (pdata && pdata->teardown) {
                ret = pdata->teardown(client, chip->gpio_chip.base,