linux-kernel - Re: [PATCH v8 01/18] drm/display: bridge_connector: Ensure last bridge determines EDID/modes detection capabilities

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Message-Id: <DFCCE8SW7MFX.ZOMBZPN1S2NX@bootlin.com>
Date: Wed, 31 Dec 2025 11:50:15 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Damon Ding" <damon.ding@...k-chips.com>, <andrzej.hajda@...el.com>,
 <neil.armstrong@...aro.org>, <rfoss@...nel.org>
Cc: <Laurent.pinchart@...asonboard.com>, <jonas@...boo.se>,
 <jernej.skrabec@...il.com>, <maarten.lankhorst@...ux.intel.com>,
 <mripard@...nel.org>, <tzimmermann@...e.de>, <airlied@...il.com>,
 <simona@...ll.ch>, <shawnguo@...nel.org>, <s.hauer@...gutronix.de>,
 <kernel@...gutronix.de>, <festevam@...il.com>, <inki.dae@...sung.com>,
 <sw0312.kim@...sung.com>, <kyungmin.park@...sung.com>, <krzk@...nel.org>,
 <alim.akhtar@...sung.com>, <jingoohan1@...il.com>,
 <p.zabel@...gutronix.de>, <hjc@...k-chips.com>, <heiko@...ech.de>,
 <andy.yan@...k-chips.com>, <dmitry.baryshkov@....qualcomm.com>,
 <dianders@...omium.org>, <m.szyprowski@...sung.com>,
 <jani.nikula@...el.com>, <linux-kernel@...r.kernel.org>,
 <dri-devel@...ts.freedesktop.org>, <imx@...ts.linux.dev>,
 <linux-arm-kernel@...ts.infradead.org>,
 <linux-samsung-soc@...r.kernel.org>, <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v8 01/18] drm/display: bridge_connector: Ensure last
 bridge determines EDID/modes detection capabilities

On Wed Dec 17, 2025 at 10:33 AM CET, Damon Ding wrote:
> When multiple bridges are present, EDID detection capability
> (DRM_BRIDGE_OP_EDID) takes precedence over modes detection
> (DRM_BRIDGE_OP_MODES). To ensure the above two capabilities are
> determined by the last bridge in the chain, we handle three cases:
>
> Case 1: The later bridge declares only DRM_BRIDGE_OP_MODES
>  - If the previous bridge declares DRM_BRIDGE_OP_EDID, set
>    &drm_bridge_connector.bridge_edid to NULL and set
>    &drm_bridge_connector.bridge_modes to the later bridge.
>  - Ensure modes detection capability of the later bridge will not
>    be ignored.
>
> Case 2: The later bridge declares only DRM_BRIDGE_OP_EDID
>  - If the previous bridge declares DRM_BRIDGE_OP_MODES, set
>    &drm_bridge_connector.bridge_modes to NULL and set
>    &drm_bridge_connector.bridge_edid to the later bridge.
>  - Although EDID detection capability has higher priority, this
>    operation is for balance and makes sense.
>
> Case 3: the later bridge declares both of them
>  - Assign later bridge as &drm_bridge_connector.bridge_edid and
>    and &drm_bridge_connector.bridge_modes to this bridge.
>  - Just leave transfer of these two capabilities as before.
>
> Signed-off-by: Damon Ding <damon.ding@...k-chips.com>
> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com