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

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Message-Id: <20251021023130.1523707-2-damon.ding@rock-chips.com>
Date: Tue, 21 Oct 2025 10:31:13 +0800
From: Damon Ding <damon.ding@...k-chips.com>
To: andrzej.hajda@...el.com,
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	Damon Ding <damon.ding@...k-chips.com>
Subject: [PATCH v7 01/18] drm/display: bridge_connector: Ensure last bridge determines EDID/modes detection capabilities

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;
+
 		if (bridge->ops & DRM_BRIDGE_OP_HDMI) {
 			if (bridge_connector->bridge_hdmi)
 				return ERR_PTR(-EBUSY);
-- 
2.34.1