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

    ...

    > diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
    > index 21ddbe440030..862ee027a02f 100644
    > --- a/include/linux/gpio/consumer.h
    > +++ b/include/linux/gpio/consumer.h
    > @@ -22,6 +22,7 @@ struct gpio_desc;
    > * gpiod_get_array().
    > */
    > struct gpio_descs {
    > + struct gpio_chip *chip;
    > unsigned int ndescs;
    > struct gpio_desc *desc[];
    > };

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