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@rock-chips.com>
Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
.../gpu/drm/display/drm_bridge_connector.c | 42 +++++++++++++++++++
1 file changed, 42 insertions(+)
diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
index baacd21e7341..0ca6f140e85b 100644
--- 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 (bridge->ops & DRM_BRIDGE_OP_HDMI) {
if (bridge_connector->bridge_hdmi)
return ERR_PTR(-EBUSY);
--
2.34.1Hello Damon,
On Tue, 30 Sep 2025 17:09:13 +0800
Damon Ding <damon.ding@rock-chips.com> 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);
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-v2-1-138b4bb70576@bootlin.com/
Best regards,
Luca
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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 <damon.ding@rock-chips.com> 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?
> 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-v2-1-138b4bb70576@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
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 <damon.ding@rock-chips.com> 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.
>
> > 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-v2-1-138b4bb70576@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
>
--
With best wishes
Dmitry
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 <damon.ding@rock-chips.com> 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-v2-1-138b4bb70576@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
Hello Damon, On Wed, 1 Oct 2025 18:09:22 +0200 Luca Ceresoli <luca.ceresoli@bootlin.com> wrote: > 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-v2-1-138b4bb70576@bootlin.com/ The patch I mentioned is now merged on drm-misc-next [1], so you'll need to rebase yours on top adapting the changes. I expect it to be simple enough, but don't hesitate to ask here in case it's not. [1] https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/2be300f9a0b6f6b0ae2a90be97e558ec0535be54 Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
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@rock-chips.com> > Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> > --- > .../gpu/drm/display/drm_bridge_connector.c | 42 +++++++++++++++++++ > 1 file changed, 42 insertions(+) > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.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
Hi Dmitry, On 10/1/2025 4:21 AM, Dmitry Baryshkov wrote: > 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@rock-chips.com> >> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> >> --- >> .../gpu/drm/display/drm_bridge_connector.c | 42 +++++++++++++++++++ >> 1 file changed, 42 insertions(+) >> > > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> > > But I'd suggest pulling this to a top of the series to let others also > take a look at it. > Will do in v7. Best regards, Damon
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