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

From: David Laight <[email-masked]>
Date: Wed, 10 Dec 2025 09:34:03 +0000

On Wed, 10 Dec 2025 06:56:17 +0100
Mika Westerberg <[email-masked]> wrote:

> $subject has typo: thunderblot -> thunderbolt ;-)
> 
> On Tue, Dec 09, 2025 at 10:03:06AM +0000, [email-masked] wrote:
> > From: David Laight <[email-masked]>
> > 
> > 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 <[email-masked]>
> > ---
> >  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