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

David Laight
2025-12-09T10:36:24Z

On Tue, 9 Dec 2025 07:56:35 +0900
Greg KH <gregkh@linuxfoundation.org> wrote:

> On Mon, Dec 08, 2025 at 10:42:43PM +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);
>
> This is going to be very confusing to people who see this line only.
> Can we add a comment here to explain why we have to do a "+ 0" and why
> it can't be removed? Otherwise I'm going to get a bunch of "cleanup"
> patches attempting to "fix" this over the next few years.

I've added a comment for v2 (but not the resend I did for the cc 'issue').
I've also fixed the subject blot => bolt.

I also noticed that the 'int thunderbolt_version:8' seems to be in a structure
that maps something read from the hardware.
That isn't going to be right on any BE system, and isn't guaranteed on LE ones.

David

>
> thanks,
>
> greg k-h