linux-kernel - Re: [PATCH v6 11/18] drm/display: bridge_connector: Ensure last bridge determines EDID/modes detection capabilities

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Message-ID: <4r25h5uaamfkprrmvrtdqfjlcgcnkfyca2o5q53hteta7rlrbq@xqlrjxhi7z2u>
Date: Tue, 30 Sep 2025 23:21:02 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Damon Ding <damon.ding@...k-chips.com>
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
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Subject: Re: [PATCH v6 11/18] drm/display: bridge_connector: Ensure last
 bridge determines EDID/modes detection capabilities

On Tue, Sep 30, 2025 at 05:09:13PM +0800, 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>
> ---
>  .../gpu/drm/display/drm_bridge_connector.c    | 42 +++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>

But I'd suggest pulling this to a top of the series to let others also
take a look at it.

-- 
With best wishes
Dmitry