linux-kernel - Re: [PATCH] drm/panel-edp: Clarify the `prepare_to

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Message-ID: <6d3e41a3-4fc0-4ebf-badc-6258ee7236cf@linaro.org>
Date: Thu, 22 May 2025 09:20:09 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Douglas Anderson <dianders@...omium.org>, dri-devel@...ts.freedesktop.org
Cc: Rob Clark <robdclark@...il.com>, David Airlie <airlied@...il.com>,
 Jessica Zhang <quic_jesszhan@...cinc.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Simona Vetter <simona@...ll.ch>,
 Thomas Zimmermann <tzimmermann@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel-edp: Clarify the `prepare_to_enable`
 description in comments

On 22/05/2025 02:32, Douglas Anderson wrote:
> It's unclear why I originally wrote in the description of
> `prepare_to_enable` that "This is not specified in a standard way on
> eDP timing diagrams" and then also wrote "It is effectively the time
> from HPD going high till you can turn on the backlight." It seems
> pretty clear that it's (T4+T5+T6+T8)-min. Either I was confused when I
> wrote this or I was looking at some strange panel datasheet that I can
> no longer find.
> 
> Update the description of the field so it's easier for people to fill
> this in. Couch the description with "usually" in case there really was
> some weird datasheet where things were specified in a different way.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>   drivers/gpu/drm/panel/panel-edp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-edp.c b/drivers/gpu/drm/panel/panel-edp.c
> index 9adbe0f11421..74f5f9006a5b 100644
> --- a/drivers/gpu/drm/panel/panel-edp.c
> +++ b/drivers/gpu/drm/panel/panel-edp.c
> @@ -113,7 +113,7 @@ struct panel_delay {
>   	 *     // do fixed enable delay
>   	 *     // enforce prepare_to_enable min time
>   	 *
> -	 * This is not specified in a standard way on eDP timing diagrams.
> +	 * This is usually (T4+T5+T6+T8)-min on eDP timing diagrams.
>   	 * It is effectively the time from HPD going high till you can
>   	 * turn on the backlight.
>   	 */

Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>