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

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Message-Id: <20251217093321.3108939-2-damon.ding@rock-chips.com>
Date: Wed, 17 Dec 2025 17:33:04 +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 v8 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.

Changes in v8:
- Adapt the modifications to the newest bridge_connector driver.
---
 drivers/gpu/drm/display/drm_bridge_connector.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
index a2d30cf9e06d..92b9e8ec520d 100644
--- a/drivers/gpu/drm/display/drm_bridge_connector.c
+++ b/drivers/gpu/drm/display/drm_bridge_connector.c
@@ -690,9 +690,19 @@ 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) {
+		/*
+		 * 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) {
 			drm_bridge_put(bridge_connector->bridge_edid);
-			bridge_connector->bridge_edid = drm_bridge_get(bridge);
+			bridge_connector->bridge_edid = NULL;
+			drm_bridge_put(bridge_connector->bridge_modes);
+			bridge_connector->bridge_modes = NULL;
+
+			if (bridge->ops & DRM_BRIDGE_OP_EDID)
+				bridge_connector->bridge_edid = drm_bridge_get(bridge);
+			if (bridge->ops & DRM_BRIDGE_OP_MODES)
+				bridge_connector->bridge_modes = drm_bridge_get(bridge);
 		}
 		if (bridge->ops & DRM_BRIDGE_OP_HPD) {
 			drm_bridge_put(bridge_connector->bridge_hpd);
@@ -702,10 +712,6 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 			drm_bridge_put(bridge_connector->bridge_detect);
 			bridge_connector->bridge_detect = drm_bridge_get(bridge);
 		}
-		if (bridge->ops & DRM_BRIDGE_OP_MODES) {
-			drm_bridge_put(bridge_connector->bridge_modes);
-			bridge_connector->bridge_modes = drm_bridge_get(bridge);
-		}
 		if (bridge->ops & DRM_BRIDGE_OP_HDMI) {
 			if (bridge_connector->bridge_hdmi)
 				return ERR_PTR(-EBUSY);
-- 
2.34.1