Re: [PATCH v4 4/8] usb: typec: Expose alternate mode priority via sysfs

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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