linux-kernel - Re: [PATCH v13 3/4] drm/atomic-helper: Re-order bridge chain pre-enable and post-disable

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Message-ID: <3adb1d12-7cd5-4beb-9978-c3cae702f338@ideasonboard.com>
Date: Mon, 16 Jun 2025 18:40:44 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Marek Szyprowski <m.szyprowski@...sung.com>,
 Aradhya Bhatia <aradhya.bhatia@...ux.dev>
Cc: DRI Development List <dri-devel@...ts.freedesktop.org>,
 Linux Kernel List <linux-kernel@...r.kernel.org>, Nishanth Menon
 <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Devarsh Thakkar <devarsht@...com>, Jayesh Choudhary <j-choudhary@...com>,
 Alexander Sverdlin <alexander.sverdlin@...mens.com>,
 Dmitry Baryshkov <lumag@...nel.org>, Andrzej Hajda
 <andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>,
 Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 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>
Subject: Re: [PATCH v13 3/4] drm/atomic-helper: Re-order bridge chain
 pre-enable and post-disable

Hi,

On 12/06/2025 09:31, Marek Szyprowski wrote:
> On 12.06.2025 07:49, Tomi Valkeinen wrote:
>> On 11/06/2025 13:45, Marek Szyprowski wrote:
>>> On 05.06.2025 19:15, Aradhya Bhatia wrote:
>>>> From: Aradhya Bhatia <a-bhatia1@...com>
>>>>
>>>> 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.
>>>>
>>>> While at it, update the drm bridge API documentation as well.
>>>>
>>>> Acked-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>>> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>>>> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
>>>> 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>
>>> This patch landed in today's linux-next as commit c9b1150a68d9
>>> ("drm/atomic-helper: Re-order bridge chain pre-enable and
>>> post-disable"). In my tests I found that it breaks booting of Samsung
>>> Exynos 5420/5800 based Chromebooks (Peach-Pit and Peach-Pi). Both of
>>> them use Exynos DRM with Exynos_DP sub-driver (Analogix DP) and EDP
>>> panel. Booting stops at '[drm] Initialized exynos 1.1.0 for exynos-drm
>>> on minor 0' message. On the other hand, the Samsung Exynos5250 based
>>> Snow Chromebook boots fine, but it uses dp-lvds nxp,ptn3460 bridge and
>>> lvds panel instead of edp panels. This looks like some sort of deadlock,
>>> because if I disable FBDEV emulation, those boards boots fine and I'm
>>> able to run modetest and enable the display. Also the DRM kernel logger
>>> seems to be working fine, although I didn't check the screen output yet,
>>> as I only have a remote access to those boards. I will investigate it
>>> further and let You know.
>> Thanks for the report. I was trying to understand the pipeline, but I'm
>> a bit confused. Above you say Peach-Pit uses DP and EDP panel, but if I
>> look at arch/arm/boot/dts/samsung/exynos5420-peach-pit.dts, it connects
>> a dp->lvds bridge (parade,ps8625). Peach-Pi seems to connect to an eDP
>> panel.
>>
>> Is the above correct? Do both Peach-Pi and Peach-Pit fail?
> 
> Yes, sorry, my fault. I much have checked the same (peach-pi) dts 2 
> times. Both Peach-Pi and Peach-Pit fails, while Snow works fine. All 
> three use the same Exynos DP (based on analogix dp) driver. I will try 
> to play a bit more with those boards in the afternoon, hopefully getting 
> some more hints where the issue is.

Did you get a chance to test this more? Any hints what happens will help =)

 Tomi