Re: [PATCH 2/3] pinctrl: Allow configuration of pins from gpiolib based drivers

[Linus Walleij]

On Thu, Jan 19, 2017 at 1:11 PM, Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> On Thu, 2017-01-19 at 12:48 +0300, Mika Westerberg wrote:
>> When a GPIO driver is backed by a pinctrl driver the GPIO driver
>> sometimes needs to call the pinctrl driver to configure certain
>> things,
>> like whether the pin is used as input or output. In addition to this
>> there are other configurations applicable to GPIOs such as setting
>> debounce time of the GPIO.
>>
>> To support this we introduce a new function pinctrl_gpio_set_config()
>> that can be used by gpiolib based driver to pass configuration
>> requests
>> to the backing pinctrl driver.
>
>
>> +     mutex_lock(&pctldev->mutex);
>> +     pin = gpio_to_pin(range, gpio);
>> +     ret = pinconf_set_config(pctldev, pin, configs,
>> ARRAY_SIZE(configs));
>> +     mutex_unlock(&pctldev->mutex);
>
> Does gpio_to_pin() require to be under lock?

All other callers do that because:

commit 9b77ace409e1419c331209c4c8eb2c8bc990e9fd
Author: Axel Lin <axel.lin@xxxxxxxxxx>
Date:   Mon Aug 19 10:07:46 2013 +0800

    pinctrl: core: Add proper mutex lock in pinctrl_request_gpio

    This one is missed in commit 42fed7ba "pinctrl: move subsystem mutex to
    pinctrl_dev struct".

    I think this fixes the race between pin_free() and pin_request() calls.
    It protects accessing the members of pctldev->desc.
    (e.g. update desc->mux_usecount, desc->gpio_owner, desc->mux_owner, etc)
    Current code grabs pctldev->mutex before calling pinmux_free_gpio(),
    but did not grab the mutex while calling pinmux_request_gpio().

    Signed-off-by: Axel Lin <axel.lin@xxxxxxxxxx>
    Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

Yours,
Linus Walleij