linux-kernel - Re: [PATCH] clocksource: Use GENMASK_ULL in definition of CLOCKSOURCE

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Message-ID: <20170417165704.GO28657@google.com>
Date:   Mon, 17 Apr 2017 09:57:04 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Dmitry Torokhov <dtor@...omium.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Grant Grundler <grundler@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>
Subject: Re: [PATCH] clocksource: Use GENMASK_ULL in definition of
 CLOCKSOURCE_MASK

Hi Dmitry,

El Fri, Apr 14, 2017 at 09:02:03PM -0700 Dmitry Torokhov ha dit:

> On Tue, Apr 11, 2017 at 12:17 PM, Matthias Kaehlcke <mka@...omium.org> wrote:
> > Besides reusing existing code this removes the special case handling
> > for 64-bit masks, which causes clang to raise a shift count overflow
> > warning due to https://bugs.llvm.org//show_bug.cgi?id=10030.
> >
> > Suggested-by: Dmitry Torokhov <dtor@...omium.org>
> > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > ---
> >  include/linux/clocksource.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> > index cfc75848a35d..06e604b9e9dc 100644
> > --- a/include/linux/clocksource.h
> > +++ b/include/linux/clocksource.h
> > @@ -120,7 +120,7 @@ struct clocksource {
> >  #define CLOCK_SOURCE_RESELECT                  0x100
> >
> >  /* simplify initialization of mask field */
> > -#define CLOCKSOURCE_MASK(bits) (u64)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
> > +#define CLOCKSOURCE_MASK(bits) (u64)GENMASK_ULL((bits) - 1, 0)
> 
> I do not think cast to u64 is needed for GENMASK_ULL.

Indeed, it is not needed, I will update the patch

Thanks!

Matthias