linux-kernel - Re: [PATCH v12 3/5] drm/atomic-helper: Re-order bridge chain pre-enable and post-disable

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Message-ID: <e245f11b-7543-4c97-864b-7c9c4cbe4943@suse.de>
Date: Wed, 4 Jun 2025 10:50:26 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Aradhya Bhatia <aradhya.bhatia@...ux.dev>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.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>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>
Cc: 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>,
 Alexander Sverdlin <alexander.sverdlin@...mens.com>,
 DRI Development List <dri-devel@...ts.freedesktop.org>,
 Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 3/5] drm/atomic-helper: Re-order bridge chain
 pre-enable and post-disable



Am 06.04.25 um 15:16 schrieb Aradhya Bhatia:
> 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>
> Tested-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@...ux.dev>

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

> ---
>   drivers/gpu/drm/drm_atomic_helper.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 86824f769623..db5aae15e75d 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1336,9 +1336,9 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *state)
>   {
>   	encoder_bridge_disable(dev, state);
>   
> -	encoder_bridge_post_disable(dev, state);
> -
>   	crtc_disable(dev, state);
> +
> +	encoder_bridge_post_disable(dev, state);
>   }
>   
>   /**
> @@ -1674,10 +1674,10 @@ encoder_bridge_enable(struct drm_device *dev, struct drm_atomic_state *state)
>   void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>   					      struct drm_atomic_state *state)
>   {
> -	crtc_enable(dev, state);
> -
>   	encoder_bridge_pre_enable(dev, state);
>   
> +	crtc_enable(dev, state);
> +
>   	encoder_bridge_enable(dev, state);
>   
>   	drm_atomic_helper_commit_writebacks(dev, state);

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)