linux-kernel - Re: [PATCH] gpio / ACPI: Return -EPROBE

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Message-ID: <5235346.FKkPIUuDpF@vostro.rjw.lan>
Date:	Thu, 11 Jun 2015 01:43:41 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Tobias Diedrich <tobiasdiedrich@...il.com>,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio / ACPI: Return -EPROBE_DEFER if the gpiochip was not found

On Wednesday, June 10, 2015 04:05:05 PM Mika Westerberg 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@...il.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

Makes sense to me.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  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.
>   */
> -
>  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)
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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