linux-kernel - Re: [PATCH v8 12/13] drm/atomic-helper: Re-order bridge chain pre-enable and post-disable

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Message-ID: <vpm37mnvo4vs6wgllgcep4y5dbxdfsblkqeolds5guwc353mbo@soxufe4jfbo6>
Date: Sun, 26 Jan 2025 23:55:49 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
Cc: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Nishanth Menon <nm@...com>, 
	Vignesh Raghavendra <vigneshr@...com>, Devarsh Thakkar <devarsht@...com>, 
	Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>, 
	Jayesh Choudhary <j-choudhary@...com>, DRI Development List <dri-devel@...ts.freedesktop.org>, 
	Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 12/13] drm/atomic-helper: Re-order bridge chain
 pre-enable and post-disable

On Mon, Jan 27, 2025 at 12:45:50AM +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.
> 
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 

I don't feel confident enough to say that I understand all the
consequences of this change. On the other hand it sounds pretty logical,
isolated and can be tested separately.

Acked-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry