Hi, On Thu, Jul 30, 2026 at 09:33:44AM +0800, Chaoyi Chen wrote: > From: Chaoyi Chen <[email protected]> > > The HPD function of Type-C DP is implemented through > drm_connector_oob_hotplug_event(). For embedded DP, it is required > that the DRM connector fwnode corresponds to the Type-C port fwnode. > > To describe the relationship between the DP controller and the Type-C > port device, we usually using drm_bridge to build a bridge chain. > > Now several USB-C controller drivers have already implemented the DP > HPD bridge function provided by aux-hpd-bridge.c, it will build a DP > HPD bridge on USB-C connector port device. > > But this requires the USB-C controller driver to manually register the > HPD bridge. If the driver does not implement this feature, the bridge > will not be create. > > So this patch implements a generic DP HPD bridge based on > aux-hpd-bridge.c. It will monitor Type-C bus events, and when a > Type-C port device containing the DP svid is registered, it will > create an HPD bridge for it without the need for the USB-C controller > driver to implement it. > > Signed-off-by: Chaoyi Chen <[email protected]> > Reviewed-by: Heikki Krogerus <[email protected]> > Reviewed-by: Nicolas Frattaroli <[email protected]> > --- > > (no changes since v5) > > Changes in v4: > - Scan the entire typec_bus and attempt to register the hpd bridge, > so as not to miss devices that were already added during initialization. > > (no changes since v3) > > Changes in v2: > - Add copyright text. > - Remove useless goto. > --- > drivers/gpu/drm/bridge/Kconfig | 10 +++ > drivers/gpu/drm/bridge/Makefile | 1 + > .../gpu/drm/bridge/aux-hpd-typec-dp-bridge.c | 64 +++++++++++++++++++ > 3 files changed, 75 insertions(+) > create mode 100644 drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c > > diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig > index 4a57d49b4c6d..9739b2a19758 100644 > --- a/drivers/gpu/drm/bridge/Kconfig > +++ b/drivers/gpu/drm/bridge/Kconfig > @@ -30,6 +30,16 @@ config DRM_AUX_HPD_BRIDGE > Simple bridge that terminates the bridge chain and provides HPD > support. > > +if DRM_AUX_HPD_BRIDGE > +config DRM_AUX_HPD_TYPEC_BRIDGE > + tristate > + depends on TYPEC || !TYPEC > + default TYPEC > + help > + Simple bridge that terminates the bridge chain and provides HPD > + support. It build bridge on each USB-C connector device node. > +endif > + > menu "Display Interface Bridges" > depends on DRM && DRM_BRIDGE > > diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile > index 15cc821d85b7..d88a9e1ccc9a 100644 > --- a/drivers/gpu/drm/bridge/Makefile > +++ b/drivers/gpu/drm/bridge/Makefile > @@ -1,6 +1,7 @@ > # SPDX-License-Identifier: GPL-2.0 > obj-$(CONFIG_DRM_AUX_BRIDGE) += aux-bridge.o > obj-$(CONFIG_DRM_AUX_HPD_BRIDGE) += aux-hpd-bridge.o > +obj-$(CONFIG_DRM_AUX_HPD_TYPEC_BRIDGE) += aux-hpd-typec-dp-bridge.o > obj-$(CONFIG_DRM_CHIPONE_ICN6211) += chipone-icn6211.o > obj-$(CONFIG_DRM_CHRONTEL_CH7033) += chrontel-ch7033.o > obj-$(CONFIG_DRM_CROS_EC_ANX7688) += cros-ec-anx7688.o > diff --git a/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c > b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c > new file mode 100644 > index 000000000000..43af3ea20f20 > --- /dev/null > +++ b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c > @@ -0,0 +1,64 @@ > +// SPDX-License-Identifier: GPL-2.0+ > +/* > + * Copyright (C) 2026 Rockchip Electronics Co., Ltd. > + * > + * Author: Chaoyi Chen <[email protected]> > + */ > +#include <linux/of.h> > +#include <linux/usb/typec_altmode.h> > +#include <linux/usb/typec_dp.h> > + > +#include <drm/bridge/aux-bridge.h> > + > +static int drm_typec_bus_event(struct notifier_block *nb, > + unsigned long action, void *data) > +{ > + struct device *dev = (struct device *)data; > + struct typec_altmode *alt = to_typec_altmode(dev); > + > + if (action != BUS_NOTIFY_ADD_DEVICE) > + return NOTIFY_OK; > + > + /* > + * alt->dev.parent->parent : USB-C controller device > + * alt->dev.parent : USB-C connector device > + */ > + if (is_typec_port_altmode(&alt->dev) && alt->svid == USB_TYPEC_DP_SID) > + drm_dp_hpd_bridge_register(alt->dev.parent->parent, > + to_of_node(alt->dev.parent->fwnode));
So there are 3 ways to end up with duplicated hpd bridges now:
1. TypeC controller driver already registered one manually
2. There is a race in drm_aux_hpd_typec_dp_bridge_module_init, if a
device appears between registering the notifier and looping
through all pre-existing devices
3. Reloading the aux-hpd-typec-dp-bridge module re-registers the
bridges
It's not a huge problem as the system works with the duplicated HPD
bridges, but it's also quite ugly.
I think it can be trivially avoided by adding this function to
drivers/gpu/drm/bridge/aux-hpd-bridge.c and then making use of it
here as an additional check (code untested):
bool drm_device_has_dp_hpd_bridge(struct device *parent)
{
struct device *hpd_bridge = device_find_child_by_name(parent,
"dp_hpd_bridge");
if (!hpd_bridge)
return false;
put_device(hpd_bridge);
return true;
}
EXPORT_SYMBOL_GPL(drm_dev_has_dp_hpd_bridge);
That would solve all of the above, but leaves one problem when this
module races against manual device creation in a TypeC controller
driver. That could be avoided by doing the check in
devm_drm_dp_hpd_bridge_alloc() under a lock, but that's probably not
worth the trouble (it would require updating all users to handle a
new error code like -EEXIST) considering manual registration can be
removed from all drivers anyways.
Greetings,
-- Sebastian
> +
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block drm_typec_event_nb = {
> + .notifier_call = drm_typec_bus_event,
> +};
> +
> +static int check_device_already_added(struct device *dev, void *data)
> +{
> + drm_typec_bus_event(NULL, BUS_NOTIFY_ADD_DEVICE, dev);
> + return 0;
> +}
> +
> +static void drm_aux_hpd_typec_dp_bridge_module_exit(void)
> +{
> + bus_unregister_notifier(&typec_bus, &drm_typec_event_nb);
> +}
> +
> +static int __init drm_aux_hpd_typec_dp_bridge_module_init(void)
> +{
> + bus_register_notifier(&typec_bus, &drm_typec_event_nb);
> + /*
> + * Before module initialization, some devices may have already been
> added.
> + * Register the HPD bridge for these devices.
> + */
> + bus_for_each_dev(&typec_bus, NULL, NULL, check_device_already_added);
> + return 0;
> +}
> +
> +module_init(drm_aux_hpd_typec_dp_bridge_module_init);
> +module_exit(drm_aux_hpd_typec_dp_bridge_module_exit);
> +
> +MODULE_AUTHOR("Chaoyi Chen <[email protected]>");
> +MODULE_DESCRIPTION("DRM TYPEC DP HPD BRIDGE");
> +MODULE_LICENSE("GPL");
> --
> 2.53.0
>
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