Messages in this thread |  | | From | Janusz Krzysztofik <> | Subject | Re: [RFC PATCH v2 12/12] gpiolib: Add fast processing path to bitmap API functions | Date | Tue, 07 Aug 2018 19:29:53 +0200 |
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On Tuesday, August 7, 2018 1:43:56 AM CEST Linus Walleij wrote: > On Tue, Aug 7, 2018 at 12:29 AM Janusz Krzysztofik <jmkrzyszt@gmail.com> wrote: > > Hi Janusz! > > > Certain GPIO descriptor arrays returned by gpio_get_array() may contain > > information on a single GPIO chip driving array member pins in hardware > > order. In such cases, bitmaps of values can be passed directly to the > > chip callback functions without wasting time on iterations. > > > > Add respective code to gpiod_get/set_array_bitmap_complex() functions. > > > > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com> > > I think it would be disappointing to leave all the users of the old > array API without the performance improvement. I think we need to > deal with this in a way such that everyone can benefit from it.
There are a few issues to be resolved:
1) array size limited by bitmap size: - are we ready to limit array size to a single bitmap for all users? - if not, how can we pass a bitmap of an arbitrary size? - if as an array of bitmaps, is that still clear enough and easy to use? - other ideas?
2) arbitrary array support: - are we ready to drop that? - if not, do we agree to require all users to pack their arbitrary arrays inside the gpio_descs structure?
Maybe more.
> Also it is kludgy if users (consumers) would need to handle the case > where all lines are on the same chip separately, through the bitmap > API.
Not true as long as array size fits (arbitrary arrays can be packed by users), but I see your point.
> What we need is an API that: > > - All drivers handling arrays can use (including current users). > > - Enables speed-up if the lines are all on the same chip/register. > > - Doesn't require consumers to know if they are all on the same > chip or not. > > This means a deep API with a small surface. > > How do we achieve this the best way?
I think widely accepted solutions to those two issues I've mentioned above can give the answer.
Thanks, Janusz
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