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>
---
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 38e101c17a004..737b76828b509 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@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 0f12d6120511b..1fb5450c0a2f2 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_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 9197a4637a938..7e6c02d74b54f 100644
--- 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;
--
2.52.0.457.g6b5491de43-googHi Andrei,
Tue, Jan 13, 2026 at 01:05:32PM +0000, Andrei Kuchynski kirjoitti:
> 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>
> ---
> 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 38e101c17a004..737b76828b509 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@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.
Greg already told you to show the range somehow with this, so the
total number of (so far known?) alternate modes. Maybe something like
<index> / <total_num_altmodes> ?
> 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 0f12d6120511b..1fb5450c0a2f2 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_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);
Please align the code properly.
> + 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;
I know not everybody likes the ternary operator, but I would just
return err ?: size;
> +}
> +
> +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 9197a4637a938..7e6c02d74b54f 100644
> --- 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;
thanks,
--
heikki
On Thu, Jan 15, 2026 at 3:34 PM Heikki Krogerus
<heikki.krogerus@linux.intel.com> wrote:
>
> Hi Andrei,
>
> Tue, Jan 13, 2026 at 01:05:32PM +0000, Andrei Kuchynski kirjoitti:
> > 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>
> > ---
> > 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 38e101c17a004..737b76828b509 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@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.
>
> Greg already told you to show the range somehow with this, so the
> total number of (so far known?) alternate modes. Maybe something like
> <index> / <total_num_altmodes> ?
>
Thank you for the review, Heikki.
Greg asked me to define a range and document it. The range is 0 to 255.
I'm not sure if this range needs to be shown.
In our current userspace application, we strictly read/write 0/1 here.
> > 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 0f12d6120511b..1fb5450c0a2f2 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_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);
>
> Please align the code properly.
>
I will. Thanks for mentioning that.
> > + 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;
>
> I know not everybody likes the ternary operator, but I would just
>
> return err ?: size;
>
I like the ternary operator. But I might keep the current implementation.
Thanks,
Andrei
On Thu, Jan 15, 2026 at 04:33:32PM +0200, Heikki Krogerus wrote:
> Hi Andrei,
>
> Tue, Jan 13, 2026 at 01:05:32PM +0000, Andrei Kuchynski kirjoitti:
> > 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>
> > ---
> > 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 38e101c17a004..737b76828b509 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@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.
>
> Greg already told you to show the range somehow with this, so the
> total number of (so far known?) alternate modes. Maybe something like
> <index> / <total_num_altmodes> ?
>
> > 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 0f12d6120511b..1fb5450c0a2f2 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_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);
>
> Please align the code properly.
>
> > + 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;
>
> I know not everybody likes the ternary operator, but I would just
>
> return err ?: size;
I hate it, so this is fine as is :)
thanks,
greg k-h
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