linux-kernel - Re: [PATCH v5 15/17] drm/bridge: analogix_dp: Remove panel disabling and enabling in analogix_dp_set

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Message-ID: <tywxkfjhulxsgdphngtfs24whslbkmnza7yx2sb7c4ulea6val@46pi6e2sjs6c>
Date: Fri, 12 Sep 2025 14:09:12 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Damon Ding <damon.ding@...k-chips.com>
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
        Laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
        simona@...ll.ch, jingoohan1@...il.com, inki.dae@...sung.com,
        sw0312.kim@...sung.com, kyungmin.park@...sung.com, krzk@...nel.org,
        alim.akhtar@...sung.com, hjc@...k-chips.com, heiko@...ech.de,
        andy.yan@...k-chips.com, dianders@...omium.org,
        m.szyprowski@...sung.com, luca.ceresoli@...tlin.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v5 15/17] drm/bridge: analogix_dp: Remove panel disabling
 and enabling in analogix_dp_set_bridge()

On Fri, Sep 12, 2025 at 04:58:44PM +0800, Damon Ding wrote:
> The &drm_panel_funcs.enable() and &drm_panel_funcs.disable() mainly
> help turn on/off the backlight to make the image visible, and the
> backlight operations are even needless if drm_panel_of_backlight() or
> drm_panel_dp_aux_backlight() is applied, in which case the enabling
> and disabling process just add necessary delays.

Not necessary, it can actually be turning the panel off and on. Maybe
it's worth squashing this patch into the panel_bridge conversion as it
will point out that these functions are still being called at a correct
times by the DRM bridge framework.

> 
> Therefore, it should make sense to remove panel disabling and move
> panel enabling after analogix_dp_set_bridge() finished.
> 
> Signed-off-by: Damon Ding <damon.ding@...k-chips.com>
> ---
>  drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> index 66d0cca1f268..c98058e9c917 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> @@ -749,9 +749,6 @@ static int analogix_dp_commit(struct analogix_dp_device *dp)
>  {
>  	int ret;
>  
> -	/* Keep the panel disabled while we configure video */
> -	drm_panel_disable(dp->plat_data->panel);
> -
>  	ret = analogix_dp_train_link(dp);
>  	if (ret) {
>  		dev_err(dp->dev, "unable to do link train, ret=%d\n", ret);
> @@ -771,9 +768,6 @@ static int analogix_dp_commit(struct analogix_dp_device *dp)
>  		return ret;
>  	}
>  
> -	/* Safe to enable the panel now */
> -	drm_panel_enable(dp->plat_data->panel);
> -
>  	/* Check whether panel supports fast training */
>  	ret = analogix_dp_fast_link_train_detection(dp);
>  	if (ret)
> @@ -1156,6 +1150,7 @@ static void analogix_dp_bridge_atomic_enable(struct drm_bridge *bridge,
>  	while (timeout_loop < MAX_PLL_LOCK_LOOP) {
>  		if (analogix_dp_set_bridge(dp) == 0) {
>  			dp->dpms_mode = DRM_MODE_DPMS_ON;
> +			drm_panel_enable(dp->plat_data->panel);
>  			return;
>  		}
>  		dev_err(dp->dev, "failed to set bridge, retry: %d\n",
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry