Hello Nicolas,
On 5/28/2026 11:37 PM, Nicolas Frattaroli wrote:
> On Wednesday, 4 March 2026 10:41:44 Central European Summer Time 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]>
>> ---
>>
>> (no changes since v14)
>>
>> Changes in v13:
>> - Only register drm dp hpd bridge for typec port altmode device.
>>
>> (no changes since v12)
>>
>> Changes in v11:
>> - Switch to using typec bus notifiers.
>>
>> (no changes since v10)
>>
>> Changes in v9:
>> - Remove the exposed DRM_AUX_HPD_BRIDGE option, and select
>> DRM_AUX_HPD_TYPEC_BRIDGE when it is available.
>> - Add more commit comment about problem background.
>>
>> Changes in v8:
>> - Merge generic DP HPD bridge into one module.
>> ---
>>
>> drivers/gpu/drm/bridge/Kconfig | 10 ++++
>> drivers/gpu/drm/bridge/Makefile | 1 +
>> .../gpu/drm/bridge/aux-hpd-typec-dp-bridge.c | 49 +++++++++++++++++++
>> 3 files changed, 60 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 a250afd8d662..559487aa09a9 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 c7dc03182e59..a3a0393d2e72 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..d915e0fb0668
>> --- /dev/null
>> +++ b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
>> @@ -0,0 +1,49 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>
> Having a copyright statement added here is likely required.
> Something like
>
> /*
> * Copyright (C) 2026 Rockchip Electronics Co., Ltd.
> *
> * Author: Chaoyi Chen <[email protected]>
> */
>
> will suffice. While I hope it's never relevant for a driver this
> small, explicit copyright statements in this form have a legal
> effect in some jurisdictions like the US, where by law it
> automatically dismisses the defense that the copyright holder
> wasn't known.
>
Oh! I hadn't noticed that. Thank you for your legal advice.
>> +#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;
>
> Small nitpick: The explicit (struct device *) cast of data isn't
> needed here. Just
>
> struct device *dev = data;
>
> will work fine. The benefit is that if the type of "data" ever changes
> (e.g. from void *data to const void *data) then we're not silencing
> a warning/error through an explicit cast.
>
Yep. Will fix in v2.
>> + struct typec_altmode *alt = to_typec_altmode(dev);
>> +
>> + if (action != BUS_NOTIFY_ADD_DEVICE)
>> + goto done;
>> +
>> + /*
>> + * 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));
>> +
>> +done:
>> + return NOTIFY_OK;
>> +}
>
> Nitpicking: the "done" label and "goto done" here is redundant.
> You could remove the label and replace the goto with another
> "return NOTIFY_OK;". There's no functional change here though.
>
Will fix in v2.
>> +
>> +static struct notifier_block drm_typec_event_nb = {
>> + .notifier_call = drm_typec_bus_event,
>> +};
>> +
>> +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);
>> +
>> + return 0;
>> +}
>> +
>> +module_init(drm_aux_hpd_typec_dp_bridge_module_init);
>> +module_exit(drm_aux_hpd_typec_dp_bridge_module_exit);
>> +
>> +MODULE_DESCRIPTION("DRM TYPEC DP HPD BRIDGE");
>> +MODULE_LICENSE("GPL");
>>
>
> Feel free to add yourself as MODULE_AUTHOR here. :)
>
> With those things changed:
>
> Reviewed-by: Nicolas Frattaroli <[email protected]>
>
> Kind regards,
> Nicolas Frattaroli
>
>
>
--
Best,
Chaoyi
