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Message-ID: <aST2RyOIjHiTv6J3@google.com>
Date: Tue, 25 Nov 2025 00:20:23 +0000
From: Benson Leung <bleung@...gle.com>
To: Andrei Kuchynski <akuchynski@...omium.org>
Cc: 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,
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
Subject: Re: [PATCH v5 4/4] usb: typec: Expose alternate mode priority via
sysfs
On Mon, Nov 24, 2025 at 12:46:39PM +0000, Andrei Kuchynski wrote:
> 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>
Reviewed-by: Benson Leung <bleung@...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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