On Sun, Nov 22, 2020 at 6:25 PM Alexandre Courbot <gnurou@xxxxxxxxx> wrote: > > The "Interacting With the Legacy GPIO Subsystem" of the documentation > was unclear at best, and even included a sentence that seems to say the > opposite of what it should say about the lifetime of the return value of > the conversion functions. > > Try to clarify things a bit and hopefully make that section more > readable. > > Signed-off-by: Alexandre Courbot <gnurou@xxxxxxxxx> Realized after sending this should also have a Reported-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx> Apologies for the omission Andy! > --- > Documentation/driver-api/gpio/consumer.rst | 18 ++++++++++-------- > 1 file changed, 10 insertions(+), 8 deletions(-) > > diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst > index 423492d125b9..173e4c7b037d 100644 > --- a/Documentation/driver-api/gpio/consumer.rst > +++ b/Documentation/driver-api/gpio/consumer.rst > @@ -440,18 +440,20 @@ For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst > > Interacting With the Legacy GPIO Subsystem > ========================================== > -Many kernel subsystems still handle GPIOs using the legacy integer-based > -interface. Although it is strongly encouraged to upgrade them to the safer > -descriptor-based API, the following two functions allow you to convert a GPIO > -descriptor into the GPIO integer namespace and vice-versa:: > +Many kernel subsystems and drivers still handle GPIOs using the legacy > +integer-based interface. It is strongly recommended to update these to the new > +gpiod interface. For cases where both interfaces need to be used, the following > +two functions allow to convert a GPIO descriptor into the GPIO integer namespace > +and vice-versa:: > > int desc_to_gpio(const struct gpio_desc *desc) > struct gpio_desc *gpio_to_desc(unsigned gpio) > > -The GPIO number returned by desc_to_gpio() can be safely used as long as the > -GPIO descriptor has not been freed. All the same, a GPIO number passed to > -gpio_to_desc() must have been properly acquired, and usage of the returned GPIO > -descriptor is only possible after the GPIO number has been released. > +The GPIO number returned by desc_to_gpio() can safely be used as a parameter of > +the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed. > +All the same, a GPIO number passed to gpio_to_desc() must first be properly > +acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only > +considered valid until that GPIO number is released using gpio_free(). > > Freeing a GPIO obtained by one API with the other API is forbidden and an > unchecked error. > -- > 2.29.2 >
