Messages in this thread |  | | From | Janusz Krzysztofik <> | Subject | Re: [RFC PATCH v2 09/12] gpiolib: Identify GPIO descriptor arrays with direct mapping | Date | Tue, 07 Aug 2018 18:50:22 +0200 |
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Hi Linus,
On Tuesday, August 7, 2018 1:29:43 AM CEST Linus Walleij wrote: > 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?
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?
Thanks, Janusz
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