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. If a new priority value conflicts with an existing
mode's priority, the priorities of the conflicting mode and all subsequent
modes are automatically incremented to ensure uniqueness.

Signed-off-by: Andrei Kuchynski <akuchynski@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://patch.msgid.link/20260119131824.2529334-4-akuchynski@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
index 38e101c17a0048d9daeec4e12896a11f85ba1e9d..737b76828b509298ed3fbc610934ea071ed63001 100644 (file)
--- 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@chromium.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 0f12d6120511b5d99763cb8a90948c3db329374e..a48c4471251840bd5ac291df3d452968e97f7911 100644 (file)
--- a/drivers/usb/typec/class.c
+++ b/drivers/usb/typec/class.c
@@ -445,11 +445,88 @@ svid_show(struct device *dev, struct device_attribute *attr, char *buf)
 }
 static DEVICE_ATTR_RO(svid);
 
+static int increment_duplicated_priority(struct device *dev, void *data)
+{
+       if (is_typec_port_altmode(dev)) {
+               struct typec_altmode **alt_target = (struct typec_altmode **)data;
+               struct typec_altmode *alt = to_typec_altmode(dev);
+
+               if (alt != *alt_target && alt->priority == (*alt_target)->priority) {
+                       alt->priority++;
+                       *alt_target = alt;
+                       return 1;
+               }
+       }
+       return 0;
+}
+
+static int find_duplicated_priority(struct device *dev, void *data)
+{
+       if (is_typec_port_altmode(dev)) {
+               struct typec_altmode **alt_target = (struct typec_altmode **)data;
+               struct typec_altmode *alt = to_typec_altmode(dev);
+
+               if (alt != *alt_target && alt->priority == (*alt_target)->priority)
+                       return 1;
+       }
+       return 0;
+}
+
+static int typec_mode_set_priority(struct typec_altmode *alt, const u8 priority)
+{
+       struct typec_port *port = to_typec_port(alt->dev.parent);
+       const u8 old_priority = alt->priority;
+       int res = 1;
+
+       alt->priority = priority;
+       while (res) {
+               res = device_for_each_child(&port->dev, &alt, find_duplicated_priority);
+               if (res) {
+                       alt->priority++;
+                       if (alt->priority == 0) {
+                               alt->priority = old_priority;
+                               return -EOVERFLOW;
+                       }
+               }
+       }
+
+       res = 1;
+       alt->priority = priority;
+       while (res)
+               res = device_for_each_child(&port->dev, &alt,
+                                           increment_duplicated_priority);
+
+       return 0;
+}
+
+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 +536,15 @@ 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;
 }
@@ -2498,6 +2579,7 @@ 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))
@@ -2516,6 +2598,12 @@ 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;

diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h
index 9197a4637a93844a4dc0974c9b8348d1f5a99525..7e6c02d74b54f7c6905ec189c1a4a1a2281358e1 100644 (file)
--- a/include/linux/usb/typec_altmode.h
+++ b/include/linux/usb/typec_altmode.h
@@ -36,6 +36,7 @@ struct typec_altmode {
        int                             mode;
        u32                             vdo;
        unsigned int                    active:1;
+       u8                              priority;
 
        char                            *desc;
        const struct typec_altmode_ops  *ops;