Re: [PATCH v3 1/3] gpio: pca953x: Rewrite ->get_multiple() function

[Paul Thomas <pthomas8589@gmail.com>]

On Tue, Apr 28, 2020 at 8:41 AM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Tue, Apr 28, 2020 at 02:13:21PM +0200, Linus Walleij wrote:
> > On Tue, Apr 21, 2020 at 5:42 PM Bartosz Golaszewski
> > <bgolaszewski@baylibre.com> wrote:
> > > wt., 21 kwi 2020 o 15:03 Andy Shevchenko
> > > <andriy.shevchenko@linux.intel.com> napisał(a):
> > > > On Mon, Apr 20, 2020 at 08:27:50PM +0300, Andy Shevchenko wrote:
>
> ...
>
> > I don't mind trying to put in code to optimize use cases
> > when accessing single bytes here either. But I'd like there
> > to be explicit comments in the code saying why these
> > optimizations are there. Can we do those on top of
> > this (hopefully) known working base?
For the record my original get_multiple patch was a known working base.

>
> As I pointed out to Paul, the optimization like he proposed is not bad thing
> per se, the implementation is. On top of that I suggested to take a look to IRQ
> status bits, which presumable will leverage from this optimization as well.
>
> So, After applying this series it would be matter of change one line in the
> ->get_multiple() to replace read_regs() with optimized version or so along with
> IRQ bits changes.

This new function would then at least need to be called with mask as
an additional argument right? Then the bitmap_replace() will set
everything regardless of if it was read, this is fine I suppose
because it doesn't matter if it's setting bits outside of mask. You
just have two loops one in the new function and one in
bitmap_replace(). If this is what people would like to see I can work
on it. I did look into the sparse reads and it seems as though regmap
has a gather_write, but not a gather_read and gather_write isn't in
regmap-i2c.c anyway.

-Paul