[PATCH AUTOSEL 6.6 28/59] pwm: sifive: Fix PWM algorithm and clarify inverted compare behavior

[Sasha Levin]

On Mon, Aug 04, 2025 at 12:45:24PM +0200, Uwe Kleine-König wrote:
>Hello,
>
>On Sun, Aug 03, 2025 at 08:33:42PM -0400, Sasha Levin wrote:
>> From: Nylon Chen <nylon.chen at sifive.com>
>>
>> [ Upstream commit 7dbc4432ea6bf9d709391eb57f1e9fb44e99845a ]
>>
>> The `frac` variable represents the pulse inactive time, and the result
>> of this algorithm is the pulse active time. Therefore, we must reverse
>> the result.
>>
>> Although the SiFive Reference Manual states "pwms >= pwmcmpX -> HIGH",
>> the hardware behavior is inverted due to a fixed XNOR with 0. As a result,
>> the pwmcmp register actually defines the low (inactive) portion of the pulse.
>>
>> The reference is SiFive FU740-C000 Manual[0]
>>
>> Link: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf [0]
>>
>> Co-developed-by: Zong Li <zong.li at sifive.com>
>> Signed-off-by: Zong Li <zong.li at sifive.com>
>> Co-developed-by: Vincent Chen <vincent.chen at sifive.com>
>> Signed-off-by: Vincent Chen <vincent.chen at sifive.com>
>> Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
>> Link: https://lore.kernel.org/r/20250529035341.51736-3-nylon.chen@sifive.com
>> Signed-off-by: Uwe Kleine-König <ukleinek at kernel.org>
>> Signed-off-by: Sasha Levin <sashal at kernel.org>
>> ---
>
>Please drop this patch from your queue, see
>https://lore.kernel.org/all/52ycm5nf2jrxdmdmcijz57xhm2twspjmmiign6zq6rp3d5wt6t@tq5w47fmiwgg/
>for the rationale.

Will do.

>This is the fourth mail of this type I'm writing. For the future: Is it
>enough to raise these concerns once only and maybe even make it easier
>on your end, too? If so, should I better pick the oldest or the newest
>base version series to reply?

Sorry about that. Just replying to just one of the mails (really doesn't
matter which) would work.

-- 
Thanks,
Sasha