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

Linus Walleij
2018-08-06T23:30:09Z

Hi Janusz!

On Tue, Aug 7, 2018 at 12:29 AM 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>
(...)
> 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;

This must be motivated: if the only purpose is to indicate to the consumer that
all GPIOs are on the same chip, why not just have a

bool all_on_same_chip;

That you set to true if these are all on the same chip?

Yours,
Linus Walleij