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

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, May 20, 2026 at 09:41:46AM +0000, Johnson Tsai wrote:
> 
> 
> 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

Wait, no, you are putting attributes in the USB interface device, which
is NOT the device your driver is creating.  Don't do that, it makes for
massive confusion.

> > 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?

The USB serial number is already exported in sysfs, why export it again
under a different filename?  That's ripe for total confusion :(

Also, where does this random UUID come from?  That's not part of the USB
spec, is it?  Why is it not just a USB string attribute like the spec
says to use for stuff like this?

thanks,

greg k-h