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

David Laight
2025-12-10T10:18:46Z

On Wed, 10 Dec 2025 10:41:02 +0100
Mika Westerberg <mika.westerberg@linux.intel.com> wrote:

> On Wed, Dec 10, 2025 at 09:34:03AM +0000, David Laight wrote:
> > 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;
>
> You mean
>
> return sw->config.thunderbolt_version >> 5;
>
> ?
>
> Yes that works but I prefer then:
>
> return sw->config.thunderbolt_version >> USB4_VERSION_MAJOR_SHIFT;

I've put that in for the next version (without the comment line).

David

>
> >
> > The only other uses of thunderbolt_version are debug prints (in decimal).
> >
> > David
> >
> > >
> > > > }
> > > >
> > > > /**
> > > > --
> > > > 2.39.5
>