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; 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]>
