linux-kernel - Re: [PATCH v3] backlight: lp855x: Switch to atomic PWM API

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Date:   Wed, 3 Nov 2021 09:32:38 -0300
From:   Maíra Canal <maira.canal@....br>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PWM List <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v3] backlight: lp855x: Switch to atomic PWM API

Em ter., 2 de nov. de 2021 às 05:39, Geert Uytterhoeven
<geert@...ux-m68k.org> escreveu:
>
> Hi Maíra,
>
> On Sat, Oct 30, 2021 at 3:35 PM Maíra Canal <maira.canal@....br> wrote:
> > Remove legacy PWM interface (pwm_config, pwm_enable, pwm_disable) and
> > replace it for the atomic PWM API.
> >
> > Signed-off-by: Maíra Canal <maira.canal@....br>
>
> Thanks for your patch!
>
> > --- a/drivers/video/backlight/lp855x_bl.c
> > +++ b/drivers/video/backlight/lp855x_bl.c
> > @@ -233,9 +233,8 @@ static int lp855x_configure(struct lp855x *lp)
> >
> >  static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)
> >  {
> > -       unsigned int period = lp->pdata->period_ns;
> > -       unsigned int duty = br * period / max_br;
> > -       struct pwm_device *pwm;
> > +       struct pwm_device *pwm = NULL;
> > +       struct pwm_state state;
> >
> >         /* request pwm device with the consumer name */
> >         if (!lp->pwm) {
> > @@ -245,18 +244,16 @@ static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)
> >
> >                 lp->pwm = pwm;
> >
> > -               /*
> > -                * FIXME: pwm_apply_args() should be removed when switching to
> > -                * the atomic PWM API.
> > -                */
> > -               pwm_apply_args(pwm);
> > +               pwm_init_state(lp->pwm, &state);
> > +               state.period = lp->pdata->period_ns;
> >         }
> >
> > -       pwm_config(lp->pwm, duty, period);
> > -       if (duty)
> > -               pwm_enable(lp->pwm);
> > -       else
> > -               pwm_disable(lp->pwm);
> > +       pwm_get_state(lp->pwm, &state);
> > +
> > +       state.duty_cycle = br * state.period / max_br;
>
> Above is a 64-by-32 division, which should not be open-coded, as
> that will cause link failures on 32-bit platform (cfr. "undefined
> reference to `__udivdi3'", as reported by the kernel test robot).
> Please use div_u64() instead.

Hi Geert,

Thank you for the suggestion! I fixed this problem a bit differently
and submitted the v4. I made use of the PWM API and applied the
pwm_set_relative_duty_cycle function, which solved this division
problem.

>
> > +       state.enabled = state.duty_cycle;
> > +
> > +       pwm_apply_state(lp->pwm, &state);
> >  }
> >
> >  static int lp855x_bl_update_status(struct backlight_device *bl)
>
> 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