Hello Sebastian, On 8/21/2026 10:55 PM, Sebastian Reichel wrote: > When the USB-C state machine finished negotiating DP AltMode before the > DRM device has been probed, the out-of-band hotplug events fired to > early and are lost. Without replugging the display or reloading the > USB-C driver, the DRM driver assumes nothing is plugged. > > Reproducing this race condition at boot time depends on kernel > configuration and exact USB-C equipment due to timing, but it can easily > be reproduced by reloading the DRM driver consuming the out-of-band > hotplug events without reloading the USB-C driver. > > Signed-off-by: Sebastian Reichel <[email protected]> > --- > This has been tested together with the patch series adding USB-C DP > AltMode support for Rockchip RK3588/RK3576. This is mostly independent > and should also affect other platforms, so I'm sending it separately. > > I ran into this during development via the module reload path, but it > seems Heiko [0] and Igor [1] managed to hit the race condition with a > normal boot. > > [0] https://lore.kernel.org/dri-devel/20767137.geO5KgaWL5@diego/ > [1] > https://lore.kernel.org/dri-devel/[email protected]/ > --- > drivers/gpu/drm/drm_connector.c | 106 > ++++++++++++++++++++++++++++++++++++ > drivers/gpu/drm/drm_crtc_internal.h | 1 + > drivers/gpu/drm/drm_drv.c | 1 + > 3 files changed, 108 insertions(+) > > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c > index 8b4baed060f3..b69e3776b153 100644 > --- a/drivers/gpu/drm/drm_connector.c > +++ b/drivers/gpu/drm/drm_connector.c > @@ -33,6 +33,7 @@ > #include <drm/drm_sysfs.h> > #include <drm/drm_utils.h> > > +#include <linux/cleanup.h> > #include <linux/export.h> > #include <linux/platform_device.h> > #include <linux/property.h> > @@ -81,6 +82,22 @@ > static DEFINE_MUTEX(connector_list_lock); > static LIST_HEAD(connector_list); > > +/* > + * List of connector fwnodes with their last out-of-band hotplug status > + * required to forward them to a connector on registration. This ensures > + * the connector sees a HPD event, if the event arrived before the DRM > + * driver was probed (either due to module reload, or because of bad > + * timing during bootup). > + */ > +struct drm_oob_hotplug_state { > + struct list_head head; > + struct fwnode_handle *fwnode; > + enum drm_connector_status status; > +}; > + > +static DEFINE_MUTEX(oob_hotplug_list_lock); > +static LIST_HEAD(oob_hotplug_list); > + > struct drm_conn_prop_enum_list { > int type; > const char *name; > @@ -130,6 +147,19 @@ void drm_connector_ida_destroy(void) > ida_destroy(&drm_connector_enum_list[i].ida); > } > > +void drm_connector_oob_hotplug_cleanup(void) > +{ > + struct drm_oob_hotplug_state *e, *tmp; > + > + scoped_guard(mutex, &oob_hotplug_list_lock) { > + list_for_each_entry_safe(e, tmp, &oob_hotplug_list, head) { > + list_del(&e->head); > + fwnode_handle_put(e->fwnode); > + kfree(e); > + } > + } > +} > + > /** > * drm_get_connector_type_name - return a string for connector type > * @type: The connector type (DRM_MODE_CONNECTOR_*) > @@ -829,6 +859,36 @@ void drm_connector_cleanup(struct drm_connector > *connector) > } > EXPORT_SYMBOL(drm_connector_cleanup); > > +/** > + * drm_connector_replay_oob_hotplug_event - send cached OOB HPD event > + * @connector: the connector that should receive the event > + * > + * Send the cached out-of-band hotplug as a new out-of-band hotplug event. > + */ > +static void drm_connector_replay_oob_hotplug_event(struct drm_connector > *connector) > +{ > + struct fwnode_handle *fwnode = connector->fwnode; > + enum drm_connector_status status; > + struct drm_oob_hotplug_state *e; > + bool found = false; > + > + if (!fwnode || !connector->funcs->oob_hotplug_event) > + return; > + > + scoped_guard(mutex, &oob_hotplug_list_lock) { > + list_for_each_entry(e, &oob_hotplug_list, head) { > + if (e->fwnode == fwnode || fwnode->secondary == > e->fwnode) { > + status = e->status; > + found = true; > + break; > + } > + } > + } > + > + if (found) > + connector->funcs->oob_hotplug_event(connector, status); > +} > + > /** > * drm_connector_register - register a connector > * @connector: the connector to register > @@ -849,6 +909,7 @@ EXPORT_SYMBOL(drm_connector_cleanup); > */ > int drm_connector_register(struct drm_connector *connector) > { > + bool replay_oob_hotplug = false; > int ret = 0; > > if (!connector->dev->registered) > @@ -888,6 +949,7 @@ int drm_connector_register(struct drm_connector > *connector) > mutex_lock(&connector_list_lock); > list_add_tail(&connector->global_connector_list_entry, &connector_list); > mutex_unlock(&connector_list_lock); > + replay_oob_hotplug = true; > goto unlock; > > err_late_register: > @@ -898,6 +960,10 @@ int drm_connector_register(struct drm_connector > *connector) > drm_sysfs_connector_remove(connector); > unlock: > mutex_unlock(&connector->mutex); > + > + if (replay_oob_hotplug) > + drm_connector_replay_oob_hotplug_event(connector); > + > return ret; > } > EXPORT_SYMBOL(drm_connector_register); > @@ -3671,6 +3737,41 @@ struct drm_connector > *drm_connector_find_by_fwnode(struct fwnode_handle *fwnode) > return found; > } > > +/** > + * drm_connector_record_oob_hotplug_status - Cache OOB hotplug status > + * @fwnode - fwnode for the DRM connector > + * @status - out-of-band status info > + * > + * Cache the latest out-of-band hotplug status for a fwnode so it can be > + * (re)played from when the DRM device is (re)registered after this event > + * arrived. > + */ > +static void drm_connector_record_oob_hotplug_status(struct fwnode_handle > *fwnode, > + enum drm_connector_status > status) > +{ > + struct drm_oob_hotplug_state *e; > + > + if (!fwnode) > + return; > + > + guard(mutex)(&oob_hotplug_list_lock); > + > + list_for_each_entry(e, &oob_hotplug_list, head) { > + if (e->fwnode == fwnode) { > + e->status = status; > + return; > + } > + } > + > + e = kzalloc(sizeof(*e), GFP_KERNEL); > + if (!e) > + return; > + > + e->fwnode = fwnode_handle_get(fwnode); > + e->status = status; > + list_add_tail(&e->head, &oob_hotplug_list); > +} > + > /** > * drm_connector_oob_hotplug_event - Report out-of-band hotplug event to > connector > * @connector_fwnode: fwnode_handle to report the event on > @@ -3683,12 +3784,17 @@ struct drm_connector > *drm_connector_find_by_fwnode(struct fwnode_handle *fwnode) > * > * This function can be used to report these out-of-band events after > obtaining > * a drm_connector reference through calling drm_connector_find_by_fwnode(). > + * > + * The last status for each fwnode is cached and replayed when a matching DRM > + * connector device is (re)registered. > */ > void drm_connector_oob_hotplug_event(struct fwnode_handle *connector_fwnode, > enum drm_connector_status status) > { > struct drm_connector *connector; > > + drm_connector_record_oob_hotplug_status(connector_fwnode, status); > + > connector = drm_connector_find_by_fwnode(connector_fwnode); > if (IS_ERR(connector)) > return;
Sorry for late reply. Should we call drm_connector_record_oob_hotplug_status() only when drm_connector_find_by_fwnode() can't find the connector? > diff --git a/drivers/gpu/drm/drm_crtc_internal.h > b/drivers/gpu/drm/drm_crtc_internal.h > index 83146ffef00c..c2714ea256a7 100644 > --- a/drivers/gpu/drm/drm_crtc_internal.h > +++ b/drivers/gpu/drm/drm_crtc_internal.h > @@ -188,6 +188,7 @@ int drm_mode_getencoder(struct drm_device *dev, > /* drm_connector.c */ > void drm_connector_ida_init(void); > void drm_connector_ida_destroy(void); > +void drm_connector_oob_hotplug_cleanup(void); > void drm_connector_unregister_all(struct drm_device *dev); > int drm_connector_register_all(struct drm_device *dev); > int drm_connector_set_obj_prop(struct drm_mode_object *obj, > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c > index 3c570f9393b9..c1aeab297ff9 100644 > --- a/drivers/gpu/drm/drm_drv.c > +++ b/drivers/gpu/drm/drm_drv.c > @@ -1239,6 +1239,7 @@ static void drm_core_exit(void) > drm_sysfs_destroy(); > WARN_ON(!xa_empty(&drm_minors_xa)); > drm_connector_ida_destroy(); > + drm_connector_oob_hotplug_cleanup(); > } > > static int __init drm_core_init(void) > > --- > base-commit: d3d1e0c4343385fb343a552e4f3b6b97d5762fc2 > change-id: 20260821-drm-connector-oob-hotplug-cache-13386679f852 > > Best regards, > -- > Sebastian Reichel <[email protected]> -- Best, Chaoyi
