Re: [PATCH v3 5/5] usb: typec: Expose alternate mode priority via sysfs

Andrei Kuchynski
2025-09-10T19:34:49Z

On Wed, Sep 10, 2025 at 1:28 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Fri, Sep 05, 2025 at 02:22:06PM +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>
> > Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> > ---
> > Documentation/ABI/testing/sysfs-class-typec | 11 +++++++
> > drivers/usb/typec/class.c | 32 ++++++++++++++++++++-
> > 2 files changed, 42 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
> > index 38e101c17a00..dab3e4e727b6 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 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.
>
> What is the units here? 0 is highest, what is the lowest? What is the
> range here? I can't determine this from the text, sorry.
>

Hi Greg,

You are right, the lowest range is not specified; the only note is that
the value should be an integer of 0 or higher.
The mode selection algorithm does not impose a maximum value. It
operates with any priority values returned by kstrtouint(). Any MAX
value would require an explanation as to why that specific value is
the maximum, and I do not have such an explanation. The only
restriction is that it must fit within an unsigned int variable, which
is checked by kstrtouint() against UINT_MAX.

> > +
> > 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 9f86605ce125..aaab2e1e98b4 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 +446,34 @@ 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) {
> > + typec_mode_set_priority(to_typec_altmode(dev), val);
> > + return size;
> > + }
> > +
> > + return err;
> > +}
> > +
> > +static ssize_t priority_show(struct device *dev,
> > + struct device_attribute *attr, char *buf)
> > +{
> > + return sprintf(buf, "%u\n", to_typec_altmode(dev)->priority);
>
> For new sysfs files, please use sysfs_emit(), otherwise someone will
> come along with a janitorial patch to fix it up after it lands in the
> tree :)
>
> thanks,
>
> greg k-h

I will change it, sysfs_emit instead of sprintf.
Thanks!

Andrei