Hi,
On 10/10/2025 10:02 PM, Dmitry Baryshkov wrote:
On Thu, Oct 09, 2025 at 12:10:42PM +0800, Damon Ding wrote:
Hi Luca,
On 10/2/2025 12:09 AM, Luca Ceresoli wrote:
Hello Damon,
On Tue, 30 Sep 2025 17:09:13 +0800
Damon Ding <[email protected]> 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.
I think the whole explanation can be more concisely rewritten as:
If the later bridge declares OP_EDID, OP_MODES or both, then both
.bridge_modes and .bridge_edid should be set to NULL (if any was set
from a previous bridge), and then .bridge_modes and/or .bridge_edid be
set to the later bridge as is done already.
Does this look correct (i.e. does it convey the same meaning)?
--- a/drivers/gpu/drm/display/drm_bridge_connector.c
+++ b/drivers/gpu/drm/display/drm_bridge_connector.c
@@ -640,6 +640,7 @@ struct drm_connector *drm_bridge_connector_init(struct
drm_device *drm,
struct drm_connector *connector;
struct i2c_adapter *ddc = NULL;
struct drm_bridge *bridge, *panel_bridge = NULL;
+ struct drm_bridge *pre_bridge_edid, *pre_bridge_modes;
unsigned int supported_formats = BIT(HDMI_COLORSPACE_RGB);
unsigned int max_bpc = 8;
bool support_hdcp = false;
@@ -668,6 +669,9 @@ struct drm_connector *drm_bridge_connector_init(struct
drm_device *drm,
*/
connector_type = DRM_MODE_CONNECTOR_Unknown;
drm_for_each_bridge_in_chain(encoder, bridge) {
+ pre_bridge_edid = bridge_connector->bridge_edid;
+ pre_bridge_modes = bridge_connector->bridge_modes;
+
if (!bridge->interlace_allowed)
connector->interlace_allowed = false;
if (!bridge->ycbcr_420_allowed)
@@ -681,6 +685,44 @@ struct drm_connector *drm_bridge_connector_init(struct
drm_device *drm,
bridge_connector->bridge_detect = bridge;
if (bridge->ops & DRM_BRIDGE_OP_MODES)
bridge_connector->bridge_modes = bridge;
+
+ /*
+ * 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 &drm_bridge_connector.bridge_modes to this bridge.
+ * - Just leave transfer of these two capabilities as before.
+ */
+ if (bridge->ops & DRM_BRIDGE_OP_EDID &&
+ !(bridge->ops & DRM_BRIDGE_OP_MODES)) {
+ if (pre_bridge_modes)
+ bridge_connector->bridge_modes = NULL;
+ }
+ if (bridge->ops & DRM_BRIDGE_OP_MODES &&
+ !(bridge->ops & DRM_BRIDGE_OP_EDID)) {
+ if (pre_bridge_edid)
+ bridge_connector->bridge_edid = NULL;
+ }
+
If the above rewrite is correct, then I think this patch can be
rewritten in a simple way (build tested only):
diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c
b/drivers/gpu/drm/display/drm_bridge_connector.c
index a5bdd6c10643..bd5dbafe88bc 100644
--- a/drivers/gpu/drm/display/drm_bridge_connector.c
+++ b/drivers/gpu/drm/display/drm_bridge_connector.c
@@ -672,14 +672,18 @@ 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;
+ 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);
Yes, this is correct and maintains functional equivalence with the previous
implementation.
I previously attempted to implement this feature by modifying the logic in
this section. However, that approach would obscure the explicit propagation
semantics of the bridge chain flags (OP_EDID/OP_HPD/OP_DETECT/OP_MODES).
Therefore, I finally decided to implemented it as a specific check after
this code block.
Dmitry, what's your take on this?
I think I prefer Luca's code, it is simpler and easier to understand. It
doesn't need a huge comment, something like "leave the last bridge which
provides either OP_EDID or OP_MODES" should be enough.
Yes, I will update the code in v7.
Another thing to note is that this patch conflicts with [0], which I
plan to apply in the next few days. The two patches are orthogonal but
they insist on the same lines (those assigning
bridge_connector->bridge_* = bridge). Not a big deal, whichever patch
comes later will be easily adapted. Just wanted to ensure you are aware.
[0]
https://lore.kernel.org/all/20250926-drm-bridge-alloc-getput-bridge-connector-v2-1-138b4bb70...@bootlin.com/
This is indeed a clever approach to the managing bridge resource cleanup in
drm_bridge_connector. Thanks a lot for the heads-up! I'll resolve this
conflict and rebase the patch series.
Apologies for the delayed reply as I was on vacation. ;-)
Best regards,
Damon
