Add a new helper to support cards implementing hotpluggable drm_bridges. drmm_hotplug_helper_init() registers to get notified of relevant events and react by creating a bridge (if the pipeline is complete in the hardware) and destroying it on bridge removal.
Signed-off-by: Luca Ceresoli <[email protected]> --- MAINTAINERS | 8 + drivers/gpu/drm/display/Kconfig | 6 + drivers/gpu/drm/display/Makefile | 2 + drivers/gpu/drm/display/drm_hotplug_helper.c | 243 +++++++++++++++++++++++++++ include/drm/drm_hotplug_helper.h | 13 ++ 5 files changed, 272 insertions(+) diff --git a/MAINTAINERS b/MAINTAINERS index c5ae9f2f408a..611790c175c4 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -8019,6 +8019,14 @@ F: Documentation/devicetree/bindings/npu/rockchip,rk3588-rknn-core.yaml F: drivers/accel/rocket/ F: include/uapi/drm/rocket_accel.h +DRM BRIDGE HOTPLUG HELPER +M: Luca Ceresoli <[email protected]> +S: Maintained +T: git https://gitlab.freedesktop.org/drm/misc/kernel.git +F: Documentation/devicetree/bindings/display/bridge/ +F: drivers/gpu/drm/display/drm_hotplug_helper.c +F: include/drm/drm_hotplug_helper.h + DRM COMPUTE ACCELERATORS DRIVERS AND FRAMEWORK M: Oded Gabbay <[email protected]> L: [email protected] diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig index df09cf9a8ca1..f1a6ffcd4c63 100644 --- a/drivers/gpu/drm/display/Kconfig +++ b/drivers/gpu/drm/display/Kconfig @@ -22,6 +22,12 @@ config DRM_BRIDGE_CONNECTOR help DRM connector implementation terminating DRM bridge chains. +config DRM_HOTPLUG_HELPER + bool + select DRM_BRIDGE_CONNECTOR + help + Helper code to implement a card supporting hotpluggable bridges. + config DRM_DISPLAY_DP_AUX_CEC bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support" select DRM_DISPLAY_DP_HELPER diff --git a/drivers/gpu/drm/display/Makefile b/drivers/gpu/drm/display/Makefile index 0ff4a1ad0222..ce6dbd65833b 100644 --- a/drivers/gpu/drm/display/Makefile +++ b/drivers/gpu/drm/display/Makefile @@ -5,6 +5,8 @@ obj-$(CONFIG_DRM_DISPLAY_DP_AUX_BUS) += drm_dp_aux_bus.o drm_display_helper-y := drm_display_helper_mod.o drm_display_helper-$(CONFIG_DRM_BRIDGE_CONNECTOR) += \ drm_bridge_connector.o +drm_display_helper-$(CONFIG_DRM_HOTPLUG_HELPER) += \ + drm_hotplug_helper.o drm_display_helper-$(CONFIG_DRM_DISPLAY_DP_HELPER) += \ drm_dp_dual_mode_helper.o \ drm_dp_helper.o \ diff --git a/drivers/gpu/drm/display/drm_hotplug_helper.c b/drivers/gpu/drm/display/drm_hotplug_helper.c new file mode 100644 index 000000000000..1b89b14b52aa --- /dev/null +++ b/drivers/gpu/drm/display/drm_hotplug_helper.c @@ -0,0 +1,243 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * Copyright (C) 2026 GE HealthCare + * Author: Luca Ceresoli <[email protected]> + */ + +#include <drm/drm_bridge.h> +#include <drm/drm_bridge_connector.h> +#include <drm/drm_event_notifier.h> +#include <drm/drm_hotplug_helper.h> +#include <drm/drm_managed.h> +#include <drm/drm_print.h> + +struct drm_hotplug_helper { + /** + * @drm: The DRM device we belong to + */ + struct drm_device *drm; + /** + * @encoder: + * + * The encoder at the start of the bridges chain. + */ + struct drm_encoder *encoder; + /** + * @drm_event_nb: notifier to receive DRM hotplug-related events + */ + struct notifier_block drm_event_nb; + /** + * @connector: the drm_connector added/removed on plug/unplug + */ + struct drm_connector *connector; + /** + * @connector_mutex: Protect @connector from concurrent creation and + * destruction + */ + struct mutex connector_mutex; +}; + +static bool drm_hotplug_helper_pipeline_is_complete(struct drm_hotplug_helper *hotplug_helper) +{ + struct drm_bridge *last_bridge __free(drm_bridge_put) = + drm_bridge_chain_get_last_bridge(hotplug_helper->encoder); + + /* We expect at least one bridge */ + if (!last_bridge) { + drm_dbg_driver(hotplug_helper->drm, "no bridges in pipeline (yet)\n"); + return false; + } + + struct drm_bridge *next_bridge __free(drm_bridge_put) = + drm_bridge_get_next(last_bridge); + + /* No next bridge expected, pipeline is complete */ + if (!next_bridge) { + drm_dbg_driver(hotplug_helper->drm, "pipeline complete\n"); + return true; + } + + /* Next bridge expected but not there now, pipeline incomplete */ + if (next_bridge == ERR_PTR(-ENODEV)) { + drm_dbg_driver(hotplug_helper->drm, "pipeline not (yet) complete\n"); + return false; + } + + /* Unexpected error */ + if (IS_ERR(next_bridge)) + drm_warn(hotplug_helper->drm, "%s error %pe\n", __func__, next_bridge); + + /* next_bridge is valid, but not (yet|anymore) in chain */ + return false; +} + +/** + * drm_hotplug_helper_connector_add - add the drm_connector + * @hotplug_helper: drm_hotplug_helper to add the drm_connector to + * + * Returns 0 on success or a negative error otherwise. + */ +static int drm_hotplug_helper_connector_add(struct drm_hotplug_helper *hotplug_helper) +{ + struct drm_connector *connector; + + guard(mutex)(&hotplug_helper->connector_mutex); + + if (drm_WARN_ON(hotplug_helper->drm, hotplug_helper->connector)) + return -EBUSY; + + connector = drm_bridge_connector_dynamic_add(hotplug_helper->drm, + hotplug_helper->encoder); + if (IS_ERR(connector)) + return PTR_ERR(connector); + + hotplug_helper->connector = connector; + + return 0; +} + +static void drm_hotplug_helper_connector_remove(struct drm_hotplug_helper *hotplug_helper) +{ + guard(mutex)(&hotplug_helper->connector_mutex); + + if (drm_WARN_ON(hotplug_helper->drm, !hotplug_helper->connector)) + return; + + drm_bridge_connector_dynamic_remove(hotplug_helper->connector); + hotplug_helper->connector = NULL; +} + +/* + * Propagate the attach chain and possibly add a drm_bridge_connector after + * a new drm_bridge is hot-plugged. + * + * The connector is added only if the pipeline is now complete. This could + * not be the case for various reasons: + * + * - the new bridge is just unrelated to our encoder + * - the new bridge is not be the next one in the pipeline + * - the new bridge is the next in the pipeline but the pipeline is not yet + * complete + * + * All these cases are normal, not an error. + */ +static void drm_hotplug_helper_try_complete(struct drm_hotplug_helper *hotplug_helper) +{ + int err; + + /* + * drm_connector already present, the new bridge must be for + * another card + */ + if (hotplug_helper->connector) + return; + + /* Propagate the attach call chain to newly hotplugged bridge(s) */ + struct drm_bridge *last_bridge __free(drm_bridge_put) = + drm_bridge_chain_get_last_bridge(hotplug_helper->encoder); + err = last_bridge->funcs->attach(last_bridge, hotplug_helper->encoder, + DRM_BRIDGE_ATTACH_NO_CONNECTOR); + if (err) + return; + + /* Add the connector if the pipeline is now complete */ + if (drm_hotplug_helper_pipeline_is_complete(hotplug_helper)) + drm_hotplug_helper_connector_add(hotplug_helper); +} + +static int drm_hotplug_helper_handle_event(struct notifier_block *nb, + unsigned long event, void *data) +{ + struct drm_hotplug_helper *hotplug_helper = + container_of(nb, struct drm_hotplug_helper, drm_event_nb); + + switch (event) { + case DRM_MIPI_DSI_ATTACHED: + /* One or more bridges hot-plugged, try adding the drm_bridge_connector */ + drm_hotplug_helper_try_complete(hotplug_helper); + break; + case DRM_BRIDGE_DETACHED: + { + /* + * A bridge was unplugged, remove the drm_bridge_connector + * if it's part of the same pipeline + */ + struct drm_bridge *bridge = (struct drm_bridge *)data; + + if (hotplug_helper->connector && + bridge->encoder == hotplug_helper->encoder) + drm_hotplug_helper_connector_remove(hotplug_helper); + break; + } + default: + } + + return NOTIFY_DONE; +} + +static void drm_hotplug_helper_fini(struct drm_device *dev, void *res) +{ + struct drm_hotplug_helper *hotplug_helper = (struct drm_hotplug_helper *)res; + + drm_hotplug_helper_connector_remove(hotplug_helper); +} + +static void drm_hotplug_helper_notifier_unregister(struct drm_device *dev, void *res) +{ + struct notifier_block *nb = (struct notifier_block *)res; + + drm_event_notifier_unregister(nb); +} + +/** + * drmm_hotplug_helper_init - Initialise the hotplug helper for an encoder + * @drm: the DRM device + * @encoder: the encoder where the bridge chain starts + * + * Register to receive hotplug-related events and react to them: + * - when a new bridge appears, check if the pipeline is now complete in + * the hardware, and if it is add a drm_bridge_connector which will add a + * drm_connector + * - when a bridge dispears, remove the drm_bridge_connector which will + * remove the drm_connector + * + * Returns a pointer to the new &drm_hotplug_helper on success, or a + * negative error pointer otherwise. + */ +struct drm_hotplug_helper *drmm_hotplug_helper_init(struct drm_device *drm, + struct drm_encoder *encoder) +{ + struct drm_hotplug_helper *hotplug_helper; + int ret; + + hotplug_helper = drmm_kzalloc(drm, sizeof(*hotplug_helper), GFP_KERNEL); + if (!hotplug_helper) + return ERR_PTR(-ENOMEM); + + mutex_init(&hotplug_helper->connector_mutex); + hotplug_helper->drm = drm; + hotplug_helper->encoder = encoder; + hotplug_helper->drm_event_nb.notifier_call = drm_hotplug_helper_handle_event; + + if (drm_hotplug_helper_pipeline_is_complete(hotplug_helper)) { + ret = drm_hotplug_helper_connector_add(hotplug_helper); + if (ret) + return ERR_PTR(ret); + } + + ret = drmm_add_action_or_reset(drm, drm_hotplug_helper_fini, hotplug_helper); + if (ret) + return ERR_PTR(ret); + + ret = drm_event_notifier_register(&hotplug_helper->drm_event_nb); + if (ret) + return ERR_PTR(ret); + + ret = drmm_add_action_or_reset(drm, drm_hotplug_helper_notifier_unregister, + &hotplug_helper->drm_event_nb); + if (ret) + return ERR_PTR(ret); + + return 0; +} +EXPORT_SYMBOL_GPL(drmm_hotplug_helper_init); diff --git a/include/drm/drm_hotplug_helper.h b/include/drm/drm_hotplug_helper.h new file mode 100644 index 000000000000..26779a0b6554 --- /dev/null +++ b/include/drm/drm_hotplug_helper.h @@ -0,0 +1,13 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Copyright (C) 2026 GE HealthCare + * Author: Luca Ceresoli <[email protected]> + */ + +#ifndef __DRM_HOTPLUG_HELPER_H__ +#define __DRM_HOTPLUG_HELPER_H__ + +struct drm_hotplug_helper *drmm_hotplug_helper_init(struct drm_device *drm, + struct drm_encoder *encoder); + +#endif /* __DRM_HOTPLUG_HELPER_H__ */ -- 2.55.0
