Re: [PATCH] drm/mediatek: mtk_dsi: Enable HS clock only at pre-enable

[Adam Thiede <me@adamthiede.com>]

On 7/28/26 10:31, AngeloGioacchino Del Regno wrote:
> Commit 76255024cadb ("drm/mediatek: mtk_dsi: enable hs clock
> during pre-enable") rightfully moves the HS clock enablement to
> before atomic_enable(), but it's moving it to mtk_dsi_poweron(),
> which is not only called in the .atomic_pre_enable() callback
> for the DRM bridge, but also in the MediaTek DRM's .ddp_start()
> callback, which happens way before the bridge ones.
> 
> The HS clock enablement should be done at just the right time,
> otherwise some bridge chips (or some Display Driver ICs) may
> not work correctly: this is seen at least with a Parade DSI to
> eDP bridge (PS8640) on the MT8173 Elm Chromebook.
> 
> This resolves a regression that was seen on the aforementioned
> machine, which was happening only after a suspend-resume cycle.
> 
> Cc: <stable@vger.kernel.org> # 7.1.x
> Fixes: 76255024cadb ("drm/mediatek: mtk_dsi: enable hs clock during pre-enable")
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> ---
>   drivers/gpu/drm/mediatek/mtk_dsi.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index dc0c4e867179..c729a163bda6 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -1165,8 +1165,6 @@ static int mtk_dsi_poweron(struct mtk_dsi *dsi)
>   		goto err_disable_dsi_and_digital_clk;
>   
>   	mtk_dsi_set_interrupt_enable(dsi);
> -	mtk_dsi_lane_ready(dsi);
> -	mtk_dsi_clk_hs_mode(dsi, 1);
>   
>   	return 0;
>   
> @@ -1284,6 +1282,9 @@ static void mtk_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
>   	ret = mtk_dsi_poweron(dsi);
>   	if (ret < 0)
>   		drm_err(drm, "failed to power on dsi\n");
> +
> +	mtk_dsi_lane_ready(dsi);
> +	mtk_dsi_clk_hs_mode(dsi, 1);
>   }
>   
>   static void mtk_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,

Tested-by: Adam Thiede <me@adamthiede.com>