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

From: "Luca Ceresoli" <luca.ceresoli@bootlin.com>
To: "Damon Ding" <damon.ding@rock-chips.com>,
	<andrzej.hajda@intel.com>, <neil.armstrong@linaro.org>,
	<rfoss@kernel.org>
Cc: <Laurent.pinchart@ideasonboard.com>, <jonas@kwiboo.se>,
	<jernej.skrabec@gmail.com>, <maarten.lankhorst@linux.intel.com>,
	<mripard@kernel.org>, <tzimmermann@suse.de>, <airlied@gmail.com>,
	<simona@ffwll.ch>, <shawnguo@kernel.org>,
	<s.hauer@pengutronix.de>, <kernel@pengutronix.de>,
	<festevam@gmail.com>, <inki.dae@samsung.com>,
	<sw0312.kim@samsung.com>, <kyungmin.park@samsung.com>,
	<krzk@kernel.org>, <alim.akhtar@samsung.com>,
	<jingoohan1@gmail.com>, <p.zabel@pengutronix.de>,
	<hjc@rock-chips.com>, <heiko@sntech.de>,
	<andy.yan@rock-chips.com>, <dmitry.baryshkov@oss.qualcomm.com>,
	<dianders@chromium.org>, <m.szyprowski@samsung.com>,
	<jani.nikula@intel.com>, <linux-kernel@vger.kernel.org>,
	<dri-devel@lists.freedesktop.org>, <imx@lists.linux.dev>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-samsung-soc@vger.kernel.org>,
	<linux-rockchip@lists.infradead.org>
Subject: Re: [PATCH v8 01/18] drm/display: bridge_connector: Ensure last bridge determines EDID/modes detection capabilities
Date: Wed, 31 Dec 2025 11:50:15 +0100	[thread overview]
Message-ID: <DFCCE8SW7MFX.ZOMBZPN1S2NX@bootlin.com> (raw)
In-Reply-To: <20251217093321.3108939-2-damon.ding@rock-chips.com>

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@rock-chips.com>
> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

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

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