On Tue, May 5, 2020 at 8:24 PM William Breathitt Gray
[off-list ref] wrote:

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

quoted

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

Regarding the question that whether width[0] and width[1] can have any
value or they are restricted to power-of-2.

Referring to the document (This xilinx GPIO IP was mentioned in the
gpio-xilinx.c file):
https://www.xilinx.com/support/documentation/ip_documentation/axi_gpio/v2_0/pg144-axi-gpio.pdf

On page 8, we can see that the GPIO widths for the 2 channels can have
values different from power-of-2.For example: 5, 15 etc.

So, I think we should keep the 'for_each_set_clump',
'bitmap_get_value' and 'bitmap_set_value' as completely generic.

I am proceeding further for my next patchset submission keeping above
findings in mind. If you guys think something else or would like to
add something, let me know.

Regards
Syed Nayyar Waris

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