[PATCH v1] usb: typec: altmodes/displayport: add irq_hpd to sysfs

[RD Babiera <rdbabiera@google.com>]

Add irq_hpd sysfs node to displayport driver. This allows the userspace
to subscribe to irq events similar to how it can subscribe to changes in
hpd.

irq_hpd is read only and returns the number of irq events generated since
driver probe. pending_irq_hpd is added so that a sysfs_emit can be
generated if the HPD high event belonging to the same status message
is delayed until a successful configuration.

Signed-off-by: RD Babiera <rdbabiera@google.com>
Reviewed-by: Badhri Jagan Sridharan <badhri@google.com>
---
 .../testing/sysfs-driver-typec-displayport    | 10 +++++++
 drivers/usb/typec/altmodes/displayport.c      | 29 +++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-driver-typec-displayport b/Documentation/ABI/testing/sysfs-driver-typec-displayport
index 256c87c5219a..314acd54e13e 100644
--- a/Documentation/ABI/testing/sysfs-driver-typec-displayport
+++ b/Documentation/ABI/testing/sysfs-driver-typec-displayport
@@ -62,3 +62,13 @@ Description:
 			     by VESA DisplayPort Alt Mode on USB Type-C Standard.
 			- 0 when HPD’s logical state is low (HPD_Low) as defined by
 			     VESA DisplayPort Alt Mode on USB Type-C Standard.
+
+What:		/sys/bus/typec/devices/.../displayport/irq_hpd
+Date:		June 2025
+Contact:	RD Babiera <rdbabiera@google.com>
+Description:
+		IRQ_HPD events are sent over the USB PD protocol in Status Update and
+		Attention messages. IRQ_HPD can only be asserted when HPD is high,
+		and is asserted when an IRQ_HPD has been issued since the last Status
+		Update. This is a read only node that returns the number of IRQ events
+		raised in the driver's lifetime.
diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index b09b58d7311d..7a04bb101337 100644
--- a/drivers/usb/typec/altmodes/displayport.c
+++ b/drivers/usb/typec/altmodes/displayport.c
@@ -65,6 +65,13 @@ struct dp_altmode {
 	enum dp_state state;
 	bool hpd;
 	bool pending_hpd;
+	u32 irq_hpd_count;
+	/*
+	 * hpd is mandatory for irq_hpd assertion, so irq_hpd also needs its own pending flag if
+	 * both hpd and irq_hpd are asserted in the first Status Update before the pin assignment
+	 * is configured.
+	 */
+	bool pending_irq_hpd;
 
 	struct mutex lock; /* device lock */
 	struct work_struct work;
@@ -151,6 +158,7 @@ static int dp_altmode_status_update(struct dp_altmode *dp)
 {
 	bool configured = !!DP_CONF_GET_PIN_ASSIGN(dp->data.conf);
 	bool hpd = !!(dp->data.status & DP_STATUS_HPD_STATE);
+	bool irq_hpd = !!(dp->data.status & DP_STATUS_IRQ_HPD);
 	u8 con = DP_STATUS_CONNECTION(dp->data.status);
 	int ret = 0;
 
@@ -170,6 +178,9 @@ static int dp_altmode_status_update(struct dp_altmode *dp)
 				dp->hpd = hpd;
 				dp->pending_hpd = true;
 			}
+			if (dp->hpd && dp->pending_hpd && irq_hpd) {
+				dp->pending_irq_hpd = true;
+			}
 		}
 	} else {
 		drm_connector_oob_hotplug_event(dp->connector_fwnode,
@@ -177,6 +188,10 @@ static int dp_altmode_status_update(struct dp_altmode *dp)
 						      connector_status_disconnected);
 		dp->hpd = hpd;
 		sysfs_notify(&dp->alt->dev.kobj, "displayport", "hpd");
+		if (hpd && irq_hpd) {
+			dp->irq_hpd_count++;
+			sysfs_notify(&dp->alt->dev.kobj, "displayport", "irq_hpd");
+		}
 	}
 
 	return ret;
@@ -196,6 +211,11 @@ static int dp_altmode_configured(struct dp_altmode *dp)
 						connector_status_connected);
 		sysfs_notify(&dp->alt->dev.kobj, "displayport", "hpd");
 		dp->pending_hpd = false;
+		if (dp->pending_irq_hpd) {
+			dp->irq_hpd_count++;
+			sysfs_notify(&dp->alt->dev.kobj, "displayport", "irq_hpd");
+			dp->pending_irq_hpd = false;
+		}
 	}
 
 	return dp_altmode_notify(dp);
@@ -707,10 +727,19 @@ static ssize_t hpd_show(struct device *dev, struct device_attribute *attr, char
 }
 static DEVICE_ATTR_RO(hpd);
 
+static ssize_t irq_hpd_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct dp_altmode *dp = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%d\n", dp->irq_hpd_count);
+}
+static DEVICE_ATTR_RO(irq_hpd);
+
 static struct attribute *displayport_attrs[] = {
 	&dev_attr_configuration.attr,
 	&dev_attr_pin_assignment.attr,
 	&dev_attr_hpd.attr,
+	&dev_attr_irq_hpd.attr,
 	NULL
 };
 

base-commit: e04c78d86a9699d136910cfc0bdcf01087e3267e
-- 
2.50.0.rc2.701.gf1e915cc24-goog