Re: [PATCH v1 5/5] usb: typec: Expose alternate mode priority via sysfs

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

Hi Andrei,

On Thu, Aug 14, 2025 at 06:44:55PM +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.
> 
> Signed-off-by: Andrei Kuchynski <akuchynski@chromium.org>
> ---
>  Documentation/ABI/testing/sysfs-class-typec | 12 ++++++
>  drivers/usb/typec/class.c                   | 47 ++++++++++++++++++++-
>  2 files changed, 58 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
> index 38e101c17a00..001202d651fa 100644
> --- a/Documentation/ABI/testing/sysfs-class-typec
> +++ b/Documentation/ABI/testing/sysfs-class-typec
> @@ -162,6 +162,18 @@ 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 alt-mode.
> +		When read, it shows the current integer priority value. Lower numerical
> +		values indicate higher priority (0 is the highest priority).
> +		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.
> +		This attribute is visible only if the kernel supports mode selection.

I was expecting this to be already used in this series.

IMO this file should be the only thing the user space needs to use by
default at least.

>  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 a72325ff099a..708f3487222a 100644
> --- a/drivers/usb/typec/class.c
> +++ b/drivers/usb/typec/class.c
> @@ -19,6 +19,7 @@
>  #include "bus.h"
>  #include "class.h"
>  #include "pd.h"
> +#include "mode_selection.h"
>  
>  static DEFINE_IDA(typec_index_ida);
>  
> @@ -445,11 +446,41 @@ svid_show(struct device *dev, struct device_attribute *attr, char *buf)
>  }
>  static DEVICE_ATTR_RO(svid);
>  
> +static ssize_t priority_store(struct device *dev,
> +			       struct device_attribute *attr,
> +			       const char *buf, size_t size)
> +{
> +	unsigned int val;
> +	int err = kstrtouint(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)
> +{
> +	int val;
> +	const int err = typec_mode_get_priority(to_typec_altmode(dev), &val);
> +
> +	if (err)
> +		return err;
> +
> +	return sprintf(buf, "%d\n", val);
> +}
> +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
>  };
>  
> @@ -458,7 +489,7 @@ static umode_t typec_altmode_attr_is_visible(struct kobject *kobj,
>  {
>  	struct typec_altmode *adev = to_typec_altmode(kobj_to_dev(kobj));
>  
> -	if (attr == &dev_attr_active.attr)
> +	if (attr == &dev_attr_active.attr) {
>  		if (!is_typec_port(adev->dev.parent)) {
>  			struct typec_partner *partner =
>  				to_typec_partner(adev->dev.parent);
> @@ -469,6 +500,15 @@ static umode_t typec_altmode_attr_is_visible(struct kobject *kobj,
>  				!adev->ops->activate)
>  				return 0444;
>  		}
> +	} else if (attr == &dev_attr_priority.attr) {
> +		if (is_typec_port(adev->dev.parent))  {
> +			struct typec_port *port = to_typec_port(adev->dev.parent);
> +
> +			if (!port->alt_mode_override)
> +				return 0;
> +		} else
> +			return 0;
> +	}

If we have the local port variable, this should be enough:

                if (!is_typec_port(adev->dev.parent) || !port->alt_mode_override)
                        return 0;

>  	return attr->mode;
>  }
> @@ -2029,6 +2069,7 @@ static void typec_release(struct device *dev)
>  	typec_mux_put(port->mux);
>  	typec_retimer_put(port->retimer);
>  	kfree(port->cap);
> +	typec_mode_selection_destroy(port);
>  	kfree(port);
>  }
>  
> @@ -2496,6 +2537,8 @@ typec_port_register_altmode(struct typec_port *port,
>  		to_altmode(adev)->retimer = retimer;
>  	}
>  
> +	typec_mode_set_priority(adev, -1);

This really should not be necessary. Why can't we set the priority
based on the order the drives registers the altmodes for the port?

>  	return adev;
>  }
>  EXPORT_SYMBOL_GPL(typec_port_register_altmode);
> @@ -2645,6 +2688,8 @@ struct typec_port *typec_register_port(struct device *parent,
>  	port->con.attach = typec_partner_attach;
>  	port->con.deattach = typec_partner_deattach;
>  
> +	INIT_LIST_HEAD(&port->mode_list);
> +
>  	if (cap->usb_capability & USB_CAPABILITY_USB4)
>  		port->usb_mode = USB_MODE_USB4;
>  	else if (cap->usb_capability & USB_CAPABILITY_USB3)

thanks,

-- 
heikki