linux-kernel - Re: [PATCH v1 3/5] drm/bridge: tc358768: Calculate video start delay

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Date:   Tue, 19 Oct 2021 11:27:44 +0200
From:   Robert Foss <robert.foss@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maxim Schwalm <maxim.schwalm@...il.com>,
        Andreas Westman Dorcsak <hedmoo@...oo.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-tegra@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/5] drm/bridge: tc358768: Calculate video start delay

On Sun, 3 Oct 2021 at 01:35, Dmitry Osipenko <digetx@...il.com> wrote:
>
> Calculate video start delay based on the display timing instead
> of hardcoding it to a default value. This fixes "trembling" display
> output on Asus Transformer TF700T which uses Panasonic VVX10F004B00
> display panel.
>
> Tested-by: Andreas Westman Dorcsak <hedmoo@...oo.com> # Asus TF700T
> Tested-by: Maxim Schwalm <maxim.schwalm@...il.com> #TF700T
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/gpu/drm/bridge/tc358768.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
> index 10ebd0621ad3..5b3f8723bd3d 100644
> --- a/drivers/gpu/drm/bridge/tc358768.c
> +++ b/drivers/gpu/drm/bridge/tc358768.c
> @@ -634,7 +634,8 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
>         u32 val, val2, lptxcnt, hact, data_type;
>         const struct drm_display_mode *mode;
>         u32 dsibclk_nsk, dsiclk_nsk, ui_nsk, phy_delay_nsk;
> -       u32 dsiclk, dsibclk;
> +       u32 dsiclk, dsibclk, video_start;
> +       const u32 internal_delay = 40;
>         int ret, i;
>
>         tc358768_hw_enable(priv);
> @@ -663,23 +664,27 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
>         case MIPI_DSI_FMT_RGB888:
>                 val |= (0x3 << 4);
>                 hact = mode->hdisplay * 3;
> +               video_start = (mode->htotal - mode->hsync_start) * 3;
>                 data_type = MIPI_DSI_PACKED_PIXEL_STREAM_24;
>                 break;
>         case MIPI_DSI_FMT_RGB666:
>                 val |= (0x4 << 4);
>                 hact = mode->hdisplay * 3;
> +               video_start = (mode->htotal - mode->hsync_start) * 3;
>                 data_type = MIPI_DSI_PACKED_PIXEL_STREAM_18;
>                 break;
>
>         case MIPI_DSI_FMT_RGB666_PACKED:
>                 val |= (0x4 << 4) | BIT(3);
>                 hact = mode->hdisplay * 18 / 8;
> +               video_start = (mode->htotal - mode->hsync_start) * 18 / 8;
>                 data_type = MIPI_DSI_PIXEL_STREAM_3BYTE_18;
>                 break;
>
>         case MIPI_DSI_FMT_RGB565:
>                 val |= (0x5 << 4);
>                 hact = mode->hdisplay * 2;
> +               video_start = (mode->htotal - mode->hsync_start) * 2;
>                 data_type = MIPI_DSI_PACKED_PIXEL_STREAM_16;
>                 break;
>         default:
> @@ -690,7 +695,8 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
>         }
>
>         /* VSDly[9:0] */
> -       tc358768_write(priv, TC358768_VSDLY, 1);
> +       video_start = max(video_start, internal_delay + 1) - internal_delay;
> +       tc358768_write(priv, TC358768_VSDLY, video_start);
>
>         tc358768_write(priv, TC358768_DATAFMT, val);
>         tc358768_write(priv, TC358768_DSITX_DT, data_type);
> --
> 2.32.0
>

Reviewed-by: Robert Foss <robert.foss@...aro.org>