linux-kernel - [PATCH v4 4/4] usb: typec: Expose alternate mode priority via sysfs

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Message-ID: <20250912064751.1987850-5-akuchynski@chromium.org>
Date: Fri, 12 Sep 2025 06:47:51 +0000
From: Andrei Kuchynski <akuchynski@...omium.org>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
	Benson Leung <bleung@...omium.org>,
	Jameson Thies <jthies@...gle.com>,
	Tzung-Bi Shih <tzungbi@...nel.org>,
	linux-usb@...r.kernel.org,
	chrome-platform@...ts.linux.dev
Cc: Guenter Roeck <groeck@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	Andrei Kuchynski <akuchynski@...omium.org>
Subject: [PATCH v4 4/4] usb: typec: Expose alternate mode priority via sysfs

This patch introduces a priority sysfs attribute to the USB Type-C
alternate mode port interface. This new attribute allows user-space to
configure the numeric priority of alternate modes managing their preferred
order of operation.

Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>
---
 Documentation/ABI/testing/sysfs-class-typec | 11 ++++++
 drivers/usb/typec/class.c                   | 37 ++++++++++++++++++++-
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
index 38e101c17a00..0f6e6adb71c4 100644
--- a/Documentation/ABI/testing/sysfs-class-typec
+++ b/Documentation/ABI/testing/sysfs-class-typec
@@ -162,6 +162,17 @@ Description:	Lists the supported USB Modes. The default USB mode that is used
 		- usb3 (USB 3.2)
 		- usb4 (USB4)
 
+		What:		/sys/class/typec/<port>/<alt-mode>/priority
+Date:		July 2025
+Contact:	Andrei Kuchynski <akuchynski@...omium.org>
+Description:
+		Displays and allows setting the priority for a specific alternate mode.
+		The priority is an integer in the range 0-255. A lower numerical value
+		indicates a higher priority (0 is the highest).
+		If the new value is already in use by another mode, the priority of the
+		conflicting mode and any subsequent modes will be incremented until they
+		are all unique.
+
 USB Type-C partner devices (eg. /sys/class/typec/port0-partner/)
 
 What:		/sys/class/typec/<port>-partner/accessory_mode
diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
index 9f86605ce125..6191f7def91c 100644
--- a/drivers/usb/typec/class.c
+++ b/drivers/usb/typec/class.c
@@ -19,6 +19,7 @@
 #include "bus.h"
 #include "class.h"
 #include "pd.h"
+#include "mode_selection.h"
 
 static DEFINE_IDA(typec_index_ida);
 
@@ -445,11 +446,34 @@ svid_show(struct device *dev, struct device_attribute *attr, char *buf)
 }
 static DEVICE_ATTR_RO(svid);
 
+static ssize_t priority_store(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t size)
+{
+	u8 val;
+	int err = kstrtou8(buf, 10, &val);
+
+	if (!err)
+		err = typec_mode_set_priority(to_typec_altmode(dev), val);
+
+	if (!err)
+		return size;
+	return err;
+}
+
+static ssize_t priority_show(struct device *dev,
+			      struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%u\n", to_typec_altmode(dev)->priority);
+}
+static DEVICE_ATTR_RW(priority);
+
 static struct attribute *typec_altmode_attrs[] = {
 	&dev_attr_active.attr,
 	&dev_attr_mode.attr,
 	&dev_attr_svid.attr,
 	&dev_attr_vdo.attr,
+	&dev_attr_priority.attr,
 	NULL
 };
 
@@ -459,11 +483,15 @@ static umode_t typec_altmode_attr_is_visible(struct kobject *kobj,
 	struct typec_altmode *adev = to_typec_altmode(kobj_to_dev(kobj));
 	struct typec_port *port = typec_altmode2port(adev);
 
-	if (attr == &dev_attr_active.attr)
+	if (attr == &dev_attr_active.attr) {
 		if (!is_typec_port(adev->dev.parent)) {
 			if (!port->mode_control || !adev->ops || !adev->ops->activate)
 				return 0444;
 		}
+	} else if (attr == &dev_attr_priority.attr) {
+		if (!is_typec_port(adev->dev.parent) || !port->mode_control)
+			return 0;
+	}
 
 	return attr->mode;
 }
@@ -2471,6 +2499,7 @@ typec_port_register_altmode(struct typec_port *port,
 	struct typec_altmode *adev;
 	struct typec_mux *mux;
 	struct typec_retimer *retimer;
+	int ret;
 
 	mux = typec_mux_get(&port->dev);
 	if (IS_ERR(mux))
@@ -2489,6 +2518,12 @@ typec_port_register_altmode(struct typec_port *port,
 	} else {
 		to_altmode(adev)->mux = mux;
 		to_altmode(adev)->retimer = retimer;
+
+		ret = typec_mode_set_priority(adev, 0);
+		if (ret) {
+			typec_unregister_altmode(adev);
+			return ERR_PTR(ret);
+		}
 	}
 
 	return adev;
-- 
2.51.0.384.g4c02a37b29-goog