[PATCH] Documentation: gpio: fix typo and unclear legacy API section

[PATCH] Documentation: gpio: fix typo and unclear legacy API section

[Alexandre Courbot]

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@gmail.com>
---
 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

Re: [PATCH] Documentation: gpio: fix typo and unclear legacy API section

[Alexandre Courbot]

On Sun, Nov 22, 2020 at 6:25 PM Alexandre Courbot <gnurou@gmail.com> 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@gmail.com>

Realized after sending this should also have a

Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>

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
>

Re: [PATCH] Documentation: gpio: fix typo and unclear legacy API section

[Andy Shevchenko]

On Sun, Nov 22, 2020 at 11:31 AM Alexandre Courbot <gnurou@gmail.com> wrote:
>
> On Sun, Nov 22, 2020 at 6:25 PM Alexandre Courbot <gnurou@gmail.com> 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@gmail.com>
>
> Realized after sending this should also have a
>
> Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
>
> Apologies for the omission Andy!

NP

And perhaps
BugLink: https://stackoverflow.com/q/64455505/2511795

>
> > ---
> >  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
> >



-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] Documentation: gpio: fix typo and unclear legacy API section

[Linus Walleij]

On Sun, Nov 22, 2020 at 10:26 AM Alexandre Courbot <gnurou@gmail.com> 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@gmail.com>

Patch applied!

Thanks for fixing this up and thanks to Andy for coordinating with
the fine folks over at StackOverflow. I added the BugLink and
Andy's Reported-by.

Yours,
Linus Walleij