linux-kernel - Re: [PATCH 2/9] thunderblot: Don't pass a bitfield to FIELD

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Message-ID: <20251210094102.GF2275908@black.igk.intel.com>
Date: Wed, 10 Dec 2025 10:41:02 +0100
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: David Laight <david.laight.linux@...il.com>
Cc: Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Crt Mori <cmo@...exis.com>,
	Richard Genoud <richard.genoud@...tlin.com>,
	Andy Shevchenko <andriy.shevchenko@...el.com>,
	Luo Jie <quic_luoj@...cinc.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	"David S . Miller" <davem@...emloft.net>,
	Simon Horman <simon.horman@...ronome.com>,
	Andreas Noever <andreas.noever@...il.com>,
	Yehezkel Bernat <YehezkelShB@...il.com>,
	Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Subject: Re: [PATCH 2/9] thunderblot: Don't pass a bitfield to FIELD_GET

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@...ux.intel.com> wrote:
> 
> > $subject has typo: thunderblot -> thunderbolt ;-)
> > 
> > On Tue, Dec 09, 2025 at 10:03:06AM +0000, david.laight.linux@...il.com wrote:
> > > From: David Laight <david.laight.linux@...il.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@...il.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;

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