Re: [PATCH 2/9] thunderblot: Don't pass a bitfield to FIELD_GET

David Laight
2025-12-10T09:34:07Z

On Wed, 10 Dec 2025 06:56:17 +0100
Mika Westerberg <mika.westerberg@linux.intel.com> wrote:

> $subject has typo: thunderblot -> thunderbolt ;-)
>
> On Tue, Dec 09, 2025 at 10:03:06AM +0000, david.laight.linux@gmail.com wrote:
> > From: David Laight <david.laight.linux@gmail.com>
> >
> > FIELD_GET needs to use __auto_type to get the value of the 'reg'
> > parameter, this can't be used with bifields.
> >
> > FIELD_GET also want to verify the size of 'reg' so can't add zero
> > to force the type to int.
> >
> > So add a zero here.
> >
> > Signed-off-by: David Laight <david.laight.linux@gmail.com>
> > ---
> > drivers/thunderbolt/tb.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
> > index e96474f17067..7ca2b5a0f01e 100644
> > --- a/drivers/thunderbolt/tb.h
> > +++ b/drivers/thunderbolt/tb.h
> > @@ -1307,7 +1307,7 @@ static inline struct tb_retimer *tb_to_retimer(struct device *dev)
> > */
> > static inline unsigned int usb4_switch_version(const struct tb_switch *sw)
> > {
> > - return FIELD_GET(USB4_VERSION_MAJOR_MASK, sw->config.thunderbolt_version);
> > + return FIELD_GET(USB4_VERSION_MAJOR_MASK, sw->config.thunderbolt_version + 0);
>
> Can't this use a cast instead? If not then can you also add a comment here
> because next someone will send a patch "fixing" the unnecessary addition.

A cast can do other (possibly incorrect) conversions, adding zero is never going
to so any 'damage' - even if it looks a bit odd.

Actually, I suspect the best thing here is to delete USB4_VERSION_MAJOR_MASK and
just do:
/* The major version is in the top 3 bits */
return sw->config.thunderbolt_version > 5;

The only other uses of thunderbolt_version are debug prints (in decimal).

David

>
> > }
> >
> > /**
> > --
> > 2.39.5