Re: [PATCH] gpiolib: don't check the retval of get_direction() when registering a chip

[Genes Lists <lists@xxxxxxxxxxxx>]

On Tue, 2025-03-11 at 18:56 +0100, Bartosz Golaszewski wrote:

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

During chip registration we should neither check the return value of

gc->get_direction() nor hold the SRCU lock when calling it. The former

is because pin controllers may have pins set to alternate functions and

return errors from their get_direction() callbacks. That's alright - we

should default to the safe INPUT state and not bail-out. The latter is

not needed because we haven't registered the chip yet so there's nothing

to protect against dynamic removal. In fact: we currently hit a lockdep

splat. Revert to calling the gc->get_direction() callback directly and

*not* checking its value.

Tested-by: Gene C <arch@xxxxxxxxxxxx>

Fixes: 9d846b1aebbe ("gpiolib: check the return value of gpio_chip::get_direction()")

Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>

Closes: https://lore.kernel.org/all/81f890fc-6688-42f0-9756-567efc8bb97a@xxxxxxxxxxx/

Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>

Link: https://lore.kernel.org/r/20250226-retval-fixes-v2-1-c8dc57182441@xxxxxxxxxx

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

---

This commit is in linux-next as 9becde08f1bc ("gpiolib: don't use

gpiochip_get_direction() when registering a chip") and was applied as

a fix to commits e623c4303ed1 ("gpiolib: sanitize the return value of

gpio_chip::get_direction()") and 9d846b1aebbe ("gpiolib: check the return

value of gpio_chip::get_direction()"). Becuase the former is queued for

v6.15-rc1, this fix was never applied to v6.14 and sent upstream.

However, the warning it addresses is now queued for v6.14. I've rebased

this commit on top of v6.14-rc6 and would like to send it upstream. Once

merged, I'll pull v6.14-rc7 back into my for-next branch and fix the

conflicts.

 drivers/gpio/gpiolib.c | 27 +++++++++++----------------

 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c

index 8741600af7ef..de708d081858 100644

--- a/drivers/gpio/gpiolib.c

+++ b/drivers/gpio/gpiolib.c

@@ -1056,24 +1056,19 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,

 

  desc->gdev = gdev;

 

- if (gc->get_direction && gpiochip_line_is_valid(gc, desc_index)) {

- ret = gc->get_direction(gc, desc_index);

- if (ret < 0)

- /*

- * FIXME: Bail-out here once all GPIO drivers

- * are updated to not return errors in

- * situations that can be considered normal

- * operation.

- */

- dev_warn(&gdev->dev,

- "%s: get_direction failed: %d\n",

- __func__, ret);

-

- assign_bit(FLAG_IS_OUT, &desc->flags, !ret);

- } else {

+ /*

+ * We would typically want to check the return value of

+ * get_direction() here but we must not check the return value

+ * and bail-out as pin controllers can have pins configured to

+ * alternate functions and return -EINVAL. Also: there's no

+ * need to take the SRCU lock here.

+ */

+ if (gc->get_direction && gpiochip_line_is_valid(gc, desc_index))

+ assign_bit(FLAG_IS_OUT, &desc->flags,

+    !gc->get_direction(gc, desc_index));

+ else

  assign_bit(FLAG_IS_OUT,

     &desc->flags, !gc->direction_input);

- }

  }

 

  ret = of_gpiochip_add(gc);

-- 

Gene

Attachment: signature.asc
Description: This is a digitally signed message part