Re: [PATCH] pwm: mtk-disp: Fix period readback

[Fei Shao]

On Thu, Aug 27, 2026 at 6:57 PM Chen-Yu Tsai <wenst@xxxxxxxxxxxx> wrote:
>
> The period value stored in the register is the number of clock cycles - 1.
>
> Account for the offset when calculating the period in nanoseconds. This
> fixes the discrepancy reported by the pwm core when CONFIG_PWM_DEBUG=1:
>
>     mediatek-disp-pwm 1100e000.pwm: .apply is not idempotent
>         (ena=1 pol=0 281500/499875) -> (ena=1 pol=0 281500/499750)
>
> Calculation discrepancy in the driver was found by AI run by a colleague
> while debugging another PWM related issue. Check against SoC datasheet
> and fix done by the author.
>
> Fixes: 3f2b16734914 ("pwm: mtk-disp: Implement atomic API .get_state()")
> Cc: Jitao Shi <jitao.shi@xxxxxxxxxxxx>
> Signed-off-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx>

Reviewed-by: Fei Shao <fshao@xxxxxxxxxxxx>