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

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Date:   Tue, 2 Nov 2021 09:39:39 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Maíra Canal <maira.canal@....br>
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

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.

> +       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