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* Re: [PATCH v3 1/5] drm/bridge: Implement generic USB Type-C DP HPD bridge
From: Sebastian Reichel @ 2026-07-17 17:19 UTC (permalink / raw)
  To: Chaoyi Chen
  Cc: Andrzej Hajda, Neil Armstrong, Robert Foss, Laurent Pinchart,
	Jonas Karlman, Jernej Skrabec, Luca Ceresoli, Maarten Lankhorst,
	Maxime Ripard, Thomas Zimmermann, David Airlie, Simona Vetter,
	Sandy Huang, Heiko Stübner, Andy Yan, Vinod Koul,
	Chaoyi Chen, Nicolas Frattaroli, linux-kernel, dri-devel,
	linux-arm-kernel, linux-rockchip, linux-phy
In-Reply-To: <20260717072323.96-2-kernel@airkyi.com>

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Hello,

On Fri, Jul 17, 2026 at 03:23:19PM +0800, Chaoyi Chen wrote:
> From: Chaoyi Chen <chaoyi.chen@rock-chips.com>
> 
> 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 <chaoyi.chen@rock-chips.com>
> Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> Reviewed-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.com> # ArmSom Sige5

I gave this a test together with the RK3588/RK3576 USB-C DP AltMode
patches I'm working on. As the fusb302 does a manual registration
for the DRM bridge in its probe function, the bridge is registered
twice:

root@sige5 # cat /sys/kernel/debug/dri/bridges
...
bridge[1]: drm_aux_hpd_bridge_funcs
	refcount: 4
	type: [10] DP
	OF: /soc/i2c@2ac50000/typec-portc@22/connector:usb-c-connector
	ops: [0x4] hpd
bridge[2]: drm_aux_hpd_bridge_funcs
	refcount: 2
	type: [10] DP
	OF: /soc/i2c@2ac50000/typec-portc@22/connector:usb-c-connector
	ops: [0x4] hpd
...

Apparently the USB-C DP AltMode keeps working, so this just wastes
a few CPU cycles and some memory. So this can land and then we can
remove the manual code from the driver as a follow-up step. I also
gave that a try and things keep working. I won't send the fusb302
patch for now to ensure its not applied before this patch lands.

Greetings,

-- Sebastian

> (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  | 54 +++++++++++++++++++
>  3 files changed, 65 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..c09579ff7ab9
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2026 Rockchip Electronics Co., Ltd.
> + *
> + * Author: Chaoyi Chen <chaoyi.chen@rock-chips.com>
> + */
> +#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));
> +
> +	return NOTIFY_OK;
> +}
> +
> +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_AUTHOR("Chaoyi Chen <chaoyi.chen@rock-chips.com>");
> +MODULE_DESCRIPTION("DRM TYPEC DP HPD BRIDGE");
> +MODULE_LICENSE("GPL");
> -- 
> 2.53.0
> 

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