Re: [PATCH v5 4/4] usb: typec: Expose alternate mode priority via sysfs

[Benson Leung <bleung@google.com>]

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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@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 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@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 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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