On Tue, 07 Aug 2018 18:50:22 +0200
Janusz Krzysztofik [off-list ref] wrote:

Hi Linus,

On Tuesday, August 7, 2018 1:29:43 AM CEST Linus Walleij wrote:

quoted

Hi Janusz!

On Tue, Aug 7, 2018 at 12:29 AM Janusz Krzysztofik [off-list ref]   

wrote:

quoted

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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>  

(...)  

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 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

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+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

quoted

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?  

My approach would probably save one or two instructions per get/set call, but 
I'm not stuck to it and will be happy to find a better solution.

How about folding the chip descriptor inside an additional structure, private 
to drivers, with internals not revealed to consumers?

Or just get the chip from gpio_descs->desc[0]->gdev->chip when
->all_on_same_chip is true...

That adds 2 dereferencing though.