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

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Message-ID: <ff65f453-68a9-41fc-b9e3-02733bba96e3@rock-chips.com>
Date: Wed, 22 Oct 2025 09:15:52 +0800
From: Damon Ding <damon.ding@...k-chips.com>
To: Luca Ceresoli <luca.ceresoli@...tlin.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

Hi Luca,

On 10/21/2025 6:31 PM, Luca Ceresoli wrote:
> 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
> 
> 

I saw your fix patches before sending this series. I think your patches 
will likely be merged relatively quickly, so I plan to wait until the 
other patches in my patch series are confirmed to be fine, then submit 
v8 version based on the latest bridge_connector driver. :-)

Best regards,
Damon