Re: [RFC PATCH v2 09/12] gpiolib: Identify GPIO descriptor arrays with direct mapping

Janusz Krzysztofik
2018-08-07T17:19:02Z

On Tuesday, August 7, 2018 7:14:20 PM CEST Boris Brezillon wrote:
> On Tue, 7 Aug 2018 00:29:15 +0200
> Janusz Krzysztofik <jmkrzyszt@gmail.com> wrote:
>
> > Certain GPIO array lookup results may map directly to GPIO pins of a
> > single GPIO chip in hardware order. If that condition is recognized
> > and handled efficiently, significant performance gain of get/set array
> > functions may be possible.
> >
> > While processing a request for an array of GPIO descriptors, verify if
> > the descriptors just collected represent consecutive pins of a single
> > GPIO chip. Pass that information with the array to the caller so it
> > can benefit from enhanced performance as soon as bitmap based get/set
> > array functions which can make efficient use of that are available.
> >
> > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
> > ---
> > Documentation/driver-api/gpio/consumer.rst | 4 +++-
> > drivers/gpio/gpiolib.c | 14 ++++++++++++++
> > include/linux/gpio/consumer.h | 1 +
> > 3 files changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst
> > index aa03f389d41d..38a990b5f3b6 100644
> > --- a/Documentation/driver-api/gpio/consumer.rst
> > +++ b/Documentation/driver-api/gpio/consumer.rst
> > @@ -109,11 +109,13 @@ For a function using multiple GPIOs all of those can be obtained with one call::
> > enum gpiod_flags flags)
> >
> > This function returns a struct gpio_descs which contains an array of
> > -descriptors::
> > +descriptors. It may also contain a valid descriptor of a single GPIO chip in
> > +case the array strictly matches pin hardware layout of the chip::
> >
> > struct gpio_descs {
> > unsigned int ndescs;
> > struct gpio_desc *desc[];
> > + struct gpio_chip *chip;
>
> chip is placed at the beginning of the struct in the real code, which
> is expected since putting it at the end won't work because of the
> desc[] declaration.

Yes, I've already noticed that and will fix on next iteration, thanks.

Janusz