On Tue, May 05, 2020 at 04:51:56PM +0300, Andy Shevchenko wrote:

On Mon, May 4, 2020 at 5:41 PM William Breathitt Gray
[off-list ref] wrote:

quoted

On Mon, May 04, 2020 at 02:41:09PM +0300, Andy Shevchenko wrote:

quoted

On Sun, May 03, 2020 at 04:38:36AM +0530, Syed Nayyar Waris wrote:

...

quoted

quoted

Looking into the last patches where we have examples I still do not see a
benefit of variadic clump sizes. power of 2 sizes would make sense (and be
optimized accordingly (64-bit, 32-bit).

--
With Best Regards,
Andy Shevchenko

There is of course benefit in defining for_each_set_clump with clump
sizes of powers of 2 (we can optimize for 32 and 64 bit sizes and avoid
boundary checks that we know will not occur), but at the very least the
variable size bitmap_set_value and bitmap_get_value provide significant
benefit for the readability of the gpio-xilinx code:

        bitmap_set_value(old, state[0], 0, width[0]);
        bitmap_set_value(old, state[1], width[0], width[1]);
        ...
        state[0] = bitmap_get_value(new, 0, width[0]);
        state[1] = bitmap_get_value(new, width[0], width[1]);

These lines are simple and clear to read: we know immediately what they
do. But if we did not have bitmap_set_value/bitmap_get_value, we'd have
to use several bitwise operations for each line; the obfuscation of the
code would be an obvious hinderance here.

Do I understand correctly that width[0] and width[1] may not be power
of two and it's actually the case?

-- 
With Best Regards,
Andy Shevchenko

I'm under the impression that width[0] and width[1] are arbitrarily
chosen by the user and could be any integer. I have never used this
hardware so I'm hoping one of the gpio-xilinx or GPIO subsystem
maintainers in this thread will respond with some guidance.

If the values of width[0] and width[1] are restricted to powers of 2,
then I agree that there is no need for generic bitmap_set_value and
bitmap_get_value functions and we can instead use more optimized power
of 2 versions.

William Breathitt Gray