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. > > > 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 > -- With best wishes Dmitry
