RE: [RFC rtw-next 1/2] wifi: rtw89: usb: add hw_info sysfs attribute

[Johnson Tsai <wenjie.tsai@realtek.com>]

On Tuesday, May 19, 2026 20:23, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Tue, May 19, 2026 at 02:11:32PM +0200, Johannes Berg wrote:
> > Hi,
> >
> > > > Example usage from user-space:
> > > >   $ cat /sys/bus/usb/devices/2-3.1.2:1.0/hw_info
> > > >   SN: 36 42 00 01 23
> > > >   UUID: aa ec 2b 7c 0a 55 47 27 8d e0 b3 0f eb cc bb aa
> >
> > Sysfs has a "one value per file" rule (soft rule according to the
> > docs, but harder in practice, I believe), so seems if anything that
> > should be two files. Maybe a UUID should also be formatted as such
> > with %pU or similar.
> 
> That should be 2 separate sysfs files please.
> 
> And yes, use %pU.

The v2 patch will use separate `sn` and `uuid` attributes, with `uuid`
formatted via `%pU`. We also removed the spaces in `sn` to provide a clean
string.

Example usage from user-space:
  $ cat /sys/bus/usb/devices/2-3.1.2:1.0/sn
  3642000123
  $ cat /sys/bus/usb/devices/2-3.1.2:1.0/uuid
  aaec2b7c-0a55-4727-8de0-b30febccbbaa

> 
> And be careful about exposing serial numbers to userspace, some systems
> don't like normal users to read them so be sure to get the permissions correct.
> We had to add some USB code for ALLOW_SERIAL_NUMBER to make it so that
> systems can handle this if they want to.
> 
> And shouldn't this just be the USB serial number to start with?  Why is there a
> different string here?  We already have a sysfs file for this value.

Regarding the serial number and permission design, these are requirements 
from Valve, so we have CC'd them here to provide the background.

Hi Elliot and Charles, could you please help explain the requirements and use case here?