linux-kernel - Re: [PATCH v7 01/18] drm/display: bridge_connector: Ensure last bridge determines EDID/modes detection capabilities

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <DDNXIYL494D2.2N8L1J7XTBT4S@bootlin.com>
Date: Tue, 21 Oct 2025 12:31:11 +0200
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 v7 01/18] drm/display: bridge_connector: Ensure last
 bridge determines EDID/modes detection capabilities

Hello Damon,

On Tue Oct 21, 2025 at 4:31 AM CEST, 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>
>
> ---
>
> Changes in v7:
> - As Luca suggested, simplify the code and related comment.
> ---
>  drivers/gpu/drm/display/drm_bridge_connector.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
> index baacd21e7341..7c2936d59517 100644
> --- a/drivers/gpu/drm/display/drm_bridge_connector.c
> +++ b/drivers/gpu/drm/display/drm_bridge_connector.c
> @@ -673,14 +673,22 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
>  		if (!bridge->ycbcr_420_allowed)
>  			connector->ycbcr_420_allowed = false;
>
> -		if (bridge->ops & DRM_BRIDGE_OP_EDID)
> -			bridge_connector->bridge_edid = bridge;
> +		/*
> +		 * Ensure the last bridge declares OP_EDID or OP_MODES or both.
> +		 */
> +		if (bridge->ops & DRM_BRIDGE_OP_EDID || bridge->ops & DRM_BRIDGE_OP_MODES) {
> +			bridge_connector->bridge_edid = NULL;
> +			bridge_connector->bridge_modes = NULL;
> +			if (bridge->ops & DRM_BRIDGE_OP_EDID)
> +				bridge_connector->bridge_edid = bridge;
> +			if (bridge->ops & DRM_BRIDGE_OP_MODES)
> +				bridge_connector->bridge_modes = bridge;
> +		}
>  		if (bridge->ops & DRM_BRIDGE_OP_HPD)
>  			bridge_connector->bridge_hpd = bridge;
>  		if (bridge->ops & DRM_BRIDGE_OP_DETECT)
>  			bridge_connector->bridge_detect = bridge;
> -		if (bridge->ops & DRM_BRIDGE_OP_MODES)
> -			bridge_connector->bridge_modes = bridge;
> +

This does not apply on current drm-misc-next, due to the patch I mentioned
in a previous iteration, now applied as commit 2be300f9a0b6 ("drm/display:
bridge_connector: get/put the stored bridges").

However I'm sorry I have to mention that patch turned out being buggy, so
I've sent a series to apply a corrected version [0]. I suggest watching the
disucssion about the fix series, and if that gets approved rebase on top of
that and adapt your changes.

Sorry about the mess. :(

[0] https://lore.kernel.org/r/20251017-drm-bridge-alloc-getput-bridge-connector-fix-hdmi_cec-v2-0-667abf6d47c0@bootlin.com

Luca

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