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

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Message-ID: <20251210101842.022d1a99@pumpkin>
Date: Wed, 10 Dec 2025 10:18:42 +0000
From: David Laight <david.laight.linux@...il.com>
To: Mika Westerberg <mika.westerberg@...ux.intel.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, 10 Dec 2025 10:41:02 +0100
Mika Westerberg <mika.westerberg@...ux.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@...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;

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    
>