Re: [PATCH 04/21] gpiolib: provide gpio_device_get_desc()

On Tue, Sep 05, 2023 at 08:52:52PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <[email protected]>
> 
> Getting the GPIO descriptor directly from the gpio_chip struct is
> dangerous as we don't take the reference to the underlying GPIO device.
> In order to start working towards removing gpiochip_get_desc(), let's
> provide a safer variant that works with an existing reference to struct
> gpio_device.

...

> +/**
> + * gpio_device_get_desc() - get the GPIO descriptor corresponding to the given
> + *                          hardware number for this GPIO device
> + * @gdev: GPIO device to get the descriptor from
> + * @hwnum: hardware number of the GPIO for this chip
> + *
> + * Returns:
> + * A pointer to the GPIO descriptor or ``ERR_PTR(-EINVAL)`` if no GPIO exists

The known constants can be referenced as %EINVAL.

> + * in the given chip for the specified hardware number or ``ERR_PTR(-ENODEV)``

Ditto.

> + * if the underlying chip already vanished.
> + *
> + * The reference count of struct gpio_device is *NOT* increased like when the
> + * GPIO is being requested for exclusive usage. It's up to the caller to make
> + * sure the GPIO device will stay alive together with the descriptor returned
> + * by this function.
> + */

-- 
With Best Regards,
Andy Shevchenko