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Message-ID: <20251124124639.1101335-5-akuchynski@chromium.org>
Date: Mon, 24 Nov 2025 12:46:39 +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>,
Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
"Christian A. Ehrhardt" <lk@...e.de>,
Abel Vesa <abel.vesa@...aro.org>,
Pooja Katiyar <pooja.katiyar@...el.com>,
Venkat Jayaraman <venkat.jayaraman@...el.com>,
linux-kernel@...r.kernel.org,
Andrei Kuchynski <akuchynski@...omium.org>
Subject: [PATCH v5 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. 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@...omium.org>
---
Documentation/ABI/testing/sysfs-class-typec | 11 +++
drivers/usb/typec/class.c | 90 ++++++++++++++++++++-
include/linux/usb/typec_altmode.h | 1 +
3 files changed, 101 insertions(+), 1 deletion(-)
diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
index 38e101c17a00..737b76828b50 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 a5327e444265..049d1829be98 100644
--- 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_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_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;
}
@@ -2484,6 +2565,7 @@ 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))
@@ -2502,6 +2584,12 @@ 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 f7db3bd4c90e..2c3b6bec2eca 100644
--- a/include/linux/usb/typec_altmode.h
+++ b/include/linux/usb/typec_altmode.h
@@ -28,6 +28,7 @@ struct typec_altmode {
int mode;
u32 vdo;
unsigned int active:1;
+ u8 priority;
char *desc;
const struct typec_altmode_ops *ops;
--
2.52.0.rc2.455.g230fcf2819-goog
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