usb: typec: altmodes/displayport: add irq_hpd to sysfs

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 <[e-mail]>
Reviewed-by: Badhri Jagan Sridharan <[e-mail]>
Reviewed-by: Heikki Krogerus <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-driver-typec-displayport

···
 			     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 <[e-mail]>
+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.

drivers/usb/typec/altmodes/displayport.c

···
 	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;
···
 {
 	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;
 
···
 				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,
···
 						      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;
···
 						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);
···
 }
 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
 };