linux-kernel - Re: [PATCH v2 2/2] pwm: sifive: change the PWM controlled LED algorithm

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Message-ID: <CAHh=Yk8cnd8Gre6yK1SNC_y=mgRNc++-dA+FdLZPfSV0OzPpFw@mail.gmail.com>
Date:   Wed, 1 Feb 2023 16:51:01 +0800
From:   Nylon Chen <nylon.chen@...ive.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     aou@...s.berkeley.edu, conor@...nel.org,
        emil.renner.berthing@...onical.com, heiko@...ech.de,
        krzysztof.kozlowski+dt@...aro.org, palmer@...belt.com,
        paul.walmsley@...ive.com, robh+dt@...nel.org,
        thierry.reding@...il.com, u.kleine-koenig@...gutronix.de,
        devicetree@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        nylon7717@...il.com, zong.li@...ive.com, greentime.hu@...ive.com,
        vincent.chen@...ive.com
Subject: Re: [PATCH v2 2/2] pwm: sifive: change the PWM controlled LED algorithm

Hi Geert,

Thanks for your reply.

Geert Uytterhoeven <geert@...ux-m68k.org> 於 2023年1月30日 週一 下午5:53寫道：
>
> Hi Nylon,
>
> On Mon, Jan 30, 2023 at 10:32 AM Nylon Chen <nylon.chen@...ive.com> wrote:
> > 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.
> >
> > The reference is SiFive FU740-C000 Manual[0].
> >
> > [0]: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf
> >
> > Signed-off-by: Nylon Chen <nylon.chen@...ive.com>
>
> Thanks for your patch!
>
> > --- a/drivers/pwm/pwm-sifive.c
> > +++ b/drivers/pwm/pwm-sifive.c
> > @@ -158,6 +158,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >         frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
> >         /* The hardware cannot generate a 100% duty cycle */
> >         frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
> > +       frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
>
> Shouldn't the inversion be done before the hardware limitation fixup?
I think your inference is correct, I will use it.

thanks a lot.
>
> >
> >         mutex_lock(&ddata->lock);
> >         if (state->period != ddata->approx_period) {
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds