linux-kernel - Re: [PATCH V6 6/6] drm: bridge: samsung-dsim: Support non-burst mode

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Date:   Tue, 16 May 2023 11:26:04 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Adam Ford <aford173@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, aford@...conembedded.com,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Inki Dae <inki.dae@...sung.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Marek Vasut <marex@...x.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 6/6] drm: bridge: samsung-dsim: Support non-burst mode

On Tue, May 16, 2023 at 7:57 AM Adam Ford <aford173@...il.com> wrote:
>
> The high-speed clock is hard-coded to the burst-clock
> frequency specified in the device tree.  However, when
> using devices like certain bridge chips without burst mode
> and varying resolutions and refresh rates, it may be
> necessary to set the high-speed clock dynamically based
> on the desired pixel clock for the connected device.
>
> This also removes the need to set a clock speed from
> the device tree for non-burst mode operation, since the
> pixel clock rate is the rate requested from the attached
> device like a bridge chip.  This should have no impact
> for people using burst-mode and setting the burst clock
> rate is still required for those users.  If the burst
> clock is not present, change the error message to
> dev_info indicating the clock use the pixel clock.
>
> Signed-off-by: Adam Ford <aford173@...il.com>
> Tested-by: Chen-Yu Tsai <wenst@...omium.org>
> Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 27 +++++++++++++++++++++------
>  1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 3944b7cfbbdf..03b21d13f067 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -655,16 +655,28 @@ static unsigned long samsung_dsim_set_pll(struct samsung_dsim *dsi,
>
>         dsi->hs_clock = fout;
>
> +       dsi->hs_clock = fout;
> +

Not sure about the double assignment. Was this caused by a rebase?

ChenYu

>         return fout;
>  }
>
>  static int samsung_dsim_enable_clock(struct samsung_dsim *dsi)
>  {
> -       unsigned long hs_clk, byte_clk, esc_clk;
> +       unsigned long hs_clk, byte_clk, esc_clk, pix_clk;
>         unsigned long esc_div;
>         u32 reg;
> +       struct drm_display_mode *m = &dsi->mode;
> +       int bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
> +
> +       /* m->clock is in KHz */
> +       pix_clk = m->clock * 1000;
> +
> +       /* Use burst_clk_rate if available, otherwise use the pix_clk */
> +       if (dsi->burst_clk_rate)
> +               hs_clk = samsung_dsim_set_pll(dsi, dsi->burst_clk_rate);
> +       else
> +               hs_clk = samsung_dsim_set_pll(dsi, DIV_ROUND_UP(pix_clk * bpp, dsi->lanes));
>
> -       hs_clk = samsung_dsim_set_pll(dsi, dsi->burst_clk_rate);
>         if (!hs_clk) {
>                 dev_err(dsi->dev, "failed to configure DSI PLL\n");
>                 return -EFAULT;
> @@ -935,7 +947,7 @@ static void samsung_dsim_set_display_mode(struct samsung_dsim *dsi)
>         u32 reg;
>
>         if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> -               int byte_clk_khz = dsi->burst_clk_rate / 1000 / 8;
> +               int byte_clk_khz = dsi->hs_clock / 1000 / 8;
>                 int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz / m->clock;
>                 int hbp = (m->htotal - m->hsync_end) * byte_clk_khz / m->clock;
>                 int hsa = (m->hsync_end - m->hsync_start) * byte_clk_khz / m->clock;
> @@ -1785,10 +1797,13 @@ static int samsung_dsim_parse_dt(struct samsung_dsim *dsi)
>                         return PTR_ERR(pll_clk);
>         }
>
> +       /* If it doesn't exist, use pixel clock instead of failing */
>         ret = samsung_dsim_of_read_u32(node, "samsung,burst-clock-frequency",
> -                                      &dsi->burst_clk_rate, 0);
> -       if (ret < 0)
> -               return ret;
> +                                      &dsi->burst_clk_rate, 1);
> +       if (ret < 0) {
> +               dev_info(dev, "Using pixel clock for HS clock frequency\n");
> +               dsi->burst_clk_rate = 0;
> +       }
>
>         ret = samsung_dsim_of_read_u32(node, "samsung,esc-clock-frequency",
>                                        &dsi->esc_clk_rate, 0);
> --
> 2.39.2
>