Re: [PATCH v6 1/8] usb: typec: Add default HPD device when register DisplayPort altmode

[Chaoyi Chen]

Hi Heikki,

On 10/20/2025 6:02 PM, Heikki Krogerus wrote:

On Thu, Oct 16, 2025 at 10:27:34AM +0800, Chaoyi Chen wrote:

From: Chaoyi Chen <chaoyi.c...@rock-chips.com>

Add default DRM AUX HPD bridge device when register DisplayPort
altmode. That makes it redundant for each Type-C driver to implement
a similar registration process in embedded scenarios.

Signed-off-by: Chaoyi Chen <chaoyi.c...@rock-chips.com>
---

Changes in v6:
- Fix depend in Kconfig.

Changes in v5:
- Remove the calls related to `drm_aux_hpd_bridge_notify()`.
- Place the helper functions in the same compilation unit.
- Add more comments about parent device.

  drivers/usb/typec/Kconfig         |  2 ++
  drivers/usb/typec/class.c         | 26 ++++++++++++++++++++++++++
  include/linux/usb/typec_altmode.h |  2 ++
  3 files changed, 30 insertions(+)

diff --git a/drivers/usb/typec/Kconfig b/drivers/usb/typec/Kconfig
index 2f80c2792dbd..a6730fbb576b 100644
--- a/drivers/usb/typec/Kconfig
+++ b/drivers/usb/typec/Kconfig
@@ -2,6 +2,8 @@

menuconfig TYPEC

        tristate "USB Type-C Support"
+       depends on DRM || DRM=n
+       select DRM_AUX_HPD_BRIDGE if DRM_BRIDGE && OF

This is wrong. DRM should not dictate how this entire subsystem core
is configured. The dependency needs to be on the DRM bridge side.

You can for example use the bus notification there to see when a new
alternate mode is being registered, or use some other notification
mechanism.

Is it a good idea to implement notification functions like 
drivers/usb/core/notify.c in TCPM, and then let other subsystems (such as DRM) 
listen to these notifications?

thanks,

        help
          USB Type-C Specification defines a cable and connector for USB where
          only one type of plug is supported on both ends, i.e. there will not
diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
index 67a533e35150..e9d7772d1a8f 100644
--- a/drivers/usb/typec/class.c
+++ b/drivers/usb/typec/class.c
@@ -8,14 +8,18 @@

#include <linux/module.h>

  #include <linux/mutex.h>
+#include <linux/of.h>
  #include <linux/property.h>
  #include <linux/slab.h>
  #include <linux/string_choices.h>
  #include <linux/usb/pd_vdo.h>
+#include <linux/usb/typec_dp.h>
  #include <linux/usb/typec_mux.h>
  #include <linux/usb/typec_retimer.h>
  #include <linux/usb.h>

+#include <drm/bridge/aux-bridge.h>

+
  #include "bus.h"
  #include "class.h"
  #include "pd.h"
@@ -538,6 +542,21 @@ const struct device_type typec_altmode_dev_type = {
        .release = typec_altmode_release,
  };

+static void dp_altmode_hpd_device_register(struct typec_altmode *alt)

+{
+       if (alt->svid != USB_TYPEC_DP_SID)
+               return;
+
+       /*
+        * alt->dev.parent->parent : USB-C controller device
+        * alt->dev.parent         : USB-C connector device
+        */
+       alt->hpd_dev = drm_dp_hpd_bridge_register(alt->dev.parent->parent,
+                                                 
to_of_node(alt->dev.parent->fwnode));
+       if (IS_ERR(alt->hpd_dev))
+               alt->hpd_dev = NULL;
+}
+
  static struct typec_altmode *
  typec_register_altmode(struct device *parent,
                       const struct typec_altmode_desc *desc)
@@ -600,6 +619,13 @@ typec_register_altmode(struct device *parent,
                return ERR_PTR(ret);
        }

+ /*

+        * It is too late to register the HPD device when the DisplayPort
+        * altmode device becomes ready. If the current altmode is DP,
+        * register a static HPD device.
+        */
+       dp_altmode_hpd_device_register(&alt->adev);
+
        return &alt->adev;
  }

diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h

index b3c0866ea70f..acb0af1b9d5d 100644
--- a/include/linux/usb/typec_altmode.h
+++ b/include/linux/usb/typec_altmode.h
@@ -21,6 +21,7 @@ struct typec_altmode_ops;
   * @desc: Optional human readable description of the mode
   * @ops: Operations vector from the driver
   * @cable_ops: Cable operations vector from the driver.
+ * @hpd_dev: HPD device for DisplayPort
   */
  struct typec_altmode {
        struct device                   dev;
@@ -32,6 +33,7 @@ struct typec_altmode {
        char                            *desc;
        const struct typec_altmode_ops  *ops;
        const struct typec_cable_ops    *cable_ops;
+       struct device                   *hpd_dev;
  };

#define to_typec_altmode(d) container_of(d, struct typec_altmode, dev)

--
2.49.0

--
Best,
Chaoyi