linux-kernel - Re: [PATCH v10 12/13] drm/atomic-helper: Re-order bridge chain pre-enable and post-disable

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Message-ID: <3fa79b755e9c6b4bfeeb38f981c4e030844f8539.camel@siemens.com>
Date: Tue, 25 Mar 2025 19:12:36 +0000
From: "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>
To: "laurent.pinchart@...asonboard.com" <laurent.pinchart@...asonboard.com>,
	"andrzej.hajda@...el.com" <andrzej.hajda@...el.com>,
	"neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
	"dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
	"tomi.valkeinen@...asonboard.com" <tomi.valkeinen@...asonboard.com>,
	"tzimmermann@...e.de" <tzimmermann@...e.de>, "simona@...ll.ch"
	<simona@...ll.ch>, "rfoss@...nel.org" <rfoss@...nel.org>, "airlied@...il.com"
	<airlied@...il.com>, "aradhya.bhatia@...ux.dev" <aradhya.bhatia@...ux.dev>,
	"jonas@...boo.se" <jonas@...boo.se>, "jernej.skrabec@...il.com"
	<jernej.skrabec@...il.com>, "mripard@...nel.org" <mripard@...nel.org>,
	"maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>
CC: "j-choudhary@...com" <j-choudhary@...com>, "u-kumar1@...com"
	<u-kumar1@...com>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "devarsht@...com" <devarsht@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "nm@...com"
	<nm@...com>, "vigneshr@...com" <vigneshr@...com>, "praneeth@...com"
	<praneeth@...com>
Subject: Re: [PATCH v10 12/13] drm/atomic-helper: Re-order bridge chain
 pre-enable and post-disable

On Wed, 2025-02-26 at 21:27 +0530, Aradhya Bhatia wrote:
> Move the bridge pre_enable call before crtc enable, and the bridge
> post_disable call after the crtc disable.
> 
> The sequence of enable after this patch will look like:
> 
> 	bridge[n]_pre_enable
> 	...
> 	bridge[1]_pre_enable
> 
> 	crtc_enable
> 	encoder_enable
> 
> 	bridge[1]_enable
> 	...
> 	bridge[n]_enable
> 
> And, the disable sequence for the display pipeline will look like:
> 
> 	bridge[n]_disable
> 	...
> 	bridge[1]_disable
> 
> 	encoder_disable
> 	crtc_disable
> 
> 	bridge[1]_post_disable
> 	...
> 	bridge[n]_post_disable
> 
> The definition of bridge pre_enable hook says that,
> "The display pipe (i.e. clocks and timing signals) feeding this bridge
> will not yet be running when this callback is called".
> 
> Since CRTC is also a source feeding the bridge, it should not be enabled
> before the bridges in the pipeline are pre_enabled. Fix that by
> re-ordering the sequence of bridge pre_enable and bridge post_disable.
> 
> Acked-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> Tested-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@...ux.dev>

Tested with AM62 OLDI series [1] on AM625 with single channel AUO 800x480
LVDS panel. No issues with the patch!

Tested-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>

[1] Link: https://lore.kernel.org/all/20250226181300.756610-1-aradhya.bhatia@linux.dev/

> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com