gpio: simplify gpiochip_export()

For some reason gpiochip_export() would invalidate all the descriptors
of a chip if exporting it to sysfs failed. This does not appear as
necessary. Remove that part of the code.

While we are at it, add a note about the non-safety of temporarily
releasing a spinlock in the middle of the loop that protects its
iterator, and explain why this is done.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 9 insertions, 11 deletions

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 3516502059f2..f150aa288fa1 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -760,18 +760,8 @@ int gpiochip_export(struct gpio_chip *chip)
         chip->exported = (status == 0);
         mutex_unlock(&sysfs_lock);
 
-        if (status) {
-                unsigned long   flags;
-                unsigned        gpio;
-
-                spin_lock_irqsave(&gpio_lock, flags);
-                gpio = 0;
-                while (gpio < chip->ngpio)
-                        chip->desc[gpio++].chip = NULL;
-                spin_unlock_irqrestore(&gpio_lock, flags);
-
+        if (status)
                 chip_dbg(chip, "%s: status %d\n", __func__, status);
-        }
 
         return status;
 }
@@ -817,6 +807,14 @@ static int __init gpiolib_sysfs_init(void)
                 if (!chip || chip->exported)
                         continue;
 
+                /*
+                 * TODO we yield gpio_lock here because gpiochip_export()
+                 * acquires a mutex. This is unsafe and needs to be fixed.
+                 *
+                 * Also it would be nice to use gpiochip_find() here so we
+                 * can keep gpio_chips local to gpiolib.c, but the yield of
+                 * gpio_lock prevents us from doing this.
+                 */
                 spin_unlock_irqrestore(&gpio_lock, flags);
                 status = gpiochip_export(chip);
                 spin_lock_irqsave(&gpio_lock, flags);