Re: [PATCH 1/2] drm: rcar-du: Restrict DPLL duty cycle workaround to H3 ES1.x

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Laurent,

On Wed, Jun 21, 2017 at 11:04 AM, Laurent Pinchart
<laurent.pinchart+renesas@ideasonboard.com> wrote:
> --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
> @@ -158,6 +157,11 @@ static void rcar_du_dpll_divider(struct rcar_du_crtc *rcrtc,
>                  best_diff);
>  }
>
> +static const struct soc_device_attribute rcar_du_r8a7795_es1[] = {
> +       { .soc_id = "r8a7795", .revision = "ES1.*" },
> +       { /* sentinel */ }
> +};
> +
>  static void rcar_du_crtc_set_display_timing(struct rcar_du_crtc *rcrtc)
>  {
>         const struct drm_display_mode *mode = &rcrtc->crtc.state->adjusted_mode;
> @@ -185,7 +189,20 @@ static void rcar_du_crtc_set_display_timing(struct rcar_du_crtc *rcrtc)
>
>                 extclk = clk_get_rate(rcrtc->extclock);
>                 if (rcdu->info->dpll_ch & (1 << rcrtc->index)) {
> -                       rcar_du_dpll_divider(rcrtc, &dpll, extclk, mode_clock);
> +                       unsigned long target = mode_clock;
> +
> +                       /*
> +                        * The H3 ES1.x exhibits dot clock duty cycle stability
> +                        * issues. We can work around them by configuring the
> +                        * DPLL to twice the desired frequency, coupled with a
> +                        * /2 post-divider. This isn't needed on other SoCs and
> +                        * breaks HDMI output on M3-W for a currently unknown
> +                        * reason, so restrict the workaround to H3 ES1.x.
> +                        */
> +                       if (soc_device_match(rcar_du_r8a7795_es1))

Matching is done over and over again, on every display enable/resume.
Can it be done at probe time?
Or in rcar_du_crtc_create(), which has access to rcrtc?

> +                               target *= 2;

You can also store the multiplier in rcar_du_r8a7795_es1.data
(store 1 in .data of the sentinel), removing the need for an if clause.

> +
> +                       rcar_du_dpll_divider(rcrtc, &dpll, extclk, target);
>                         extclk = dpll.output;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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
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