Re: [PATCH] gpio / ACPI: Return -EPROBE_DEFER if the gpiochip was not found

[Amos Jianjun Kong <kongjianjun@xxxxxxxxx>]

On Wed, Jun 10, 2015 at 9:05 PM, Mika Westerberg
<mika.westerberg@xxxxxxxxxxxxxxx> wrote:
> If a driver requests a GPIO described in its _CRS but the GPIO host
> controller (gpiochip) driver providing the GPIO has not been loaded yet
> acpi_get_gpiod() returns -ENODEV which causes the calling driver to fail.
>
> If the gpiochip driver is loaded afterwards the driver requesting the GPIO
> will not notice this.
>
> Better approach is to return -EPROBE_DEFER in such case. Then when the
> gpiochip driver appears the driver requesting the GPIO will be probed
> again. This also aligns ACPI GPIO lookup code closer to DT as it does
> pretty much the same when no gpiochip driver was found.
>
> Reported-by: Tobias Diedrich <tobiasdiedrich@xxxxxxxxx>
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> ---
>  drivers/gpio/gpiolib-acpi.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-acpi.c b/drivers/gpio/gpiolib-acpi.c
> index 19b99d0c2bf0..b49006c81a7f 100644
> --- a/drivers/gpio/gpiolib-acpi.c
> +++ b/drivers/gpio/gpiolib-acpi.c
> @@ -114,10 +114,11 @@ static inline int acpi_gpiochip_pin_to_gpio_offset(struct gpio_chip *chip,
>   * @path:      ACPI GPIO controller full path name, (e.g. "\\_SB.GPO1")
>   * @pin:       ACPI GPIO pin number (0-based, controller-relative)
>   *
> - * Returns GPIO descriptor to use with Linux generic GPIO API, or ERR_PTR
> - * error value
> + * Return: GPIO descriptor to use with Linux generic GPIO API, or ERR_PTR
> + * error value. Specifically returns %-EPROBE_DEFER if the referenced GPIO
> + * controller does not have gpiochip registered at the moment. This is to
> + * support probe deferral.
>   */
> -

api_get_gpiod() is called in preprobe stage, we still have chance to
probe the device.

Reviewed-by: Amos Kong <kongjianjun@xxxxxxxxx>

>  static struct gpio_desc *acpi_get_gpiod(char *path, int pin)
>  {
>         struct gpio_chip *chip;
> @@ -131,7 +132,7 @@ static struct gpio_desc *acpi_get_gpiod(char *path, int pin)
>
>         chip = gpiochip_find(handle, acpi_gpiochip_find);
>         if (!chip)
> -               return ERR_PTR(-ENODEV);
> +               return ERR_PTR(-EPROBE_DEFER);
>
>         offset = acpi_gpiochip_pin_to_gpio_offset(chip, pin);
>         if (offset < 0)
> --
> 2.1.4
>
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