linux-kernel - Re: [PATCH] s390: Simplify the calculation of variables

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Date:   Mon, 4 Apr 2022 11:10:55 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "'Haowen Bai'" <baihaowen@...zu.com>,
        "gor@...ux.ibm.com" <gor@...ux.ibm.com>,
        "agordeev@...ux.ibm.com" <agordeev@...ux.ibm.com>,
        "borntraeger@...ux.ibm.com" <borntraeger@...ux.ibm.com>,
        "svens@...ux.ibm.com" <svens@...ux.ibm.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>
Subject: Re: [PATCH] s390: Simplify the calculation of variables

On Mon, Mar 28, 2022 at 12:15:49PM +0000, David Laight wrote:
> From: Haowen Bai
> > Sent: 28 March 2022 03:36
> > 
> > Fix the following coccicheck warnings:
> > ./arch/s390/include/asm/scsw.h:695:47-49: WARNING
> >  !A || A && B is equivalent to !A || B
> > 
> > Signed-off-by: Haowen Bai <baihaowen@...zu.com>
> > ---
> >  arch/s390/include/asm/scsw.h | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/arch/s390/include/asm/scsw.h b/arch/s390/include/asm/scsw.h
> > index a7c3ccf..f2baac8 100644
> > --- a/arch/s390/include/asm/scsw.h
> > +++ b/arch/s390/include/asm/scsw.h
> > @@ -692,8 +692,7 @@ static inline int scsw_tm_is_valid_pno(union scsw *scsw)
> >  	return (scsw->tm.fctl != 0) &&
> >  	       (scsw->tm.stctl & SCSW_STCTL_STATUS_PEND) &&
> >  	       (!(scsw->tm.stctl & SCSW_STCTL_INTER_STATUS) ||
> > -		 ((scsw->tm.stctl & SCSW_STCTL_INTER_STATUS) &&
> > -		  (scsw->tm.actl & SCSW_ACTL_SUSPENDED)));
> > +	       (scsw->tm.actl & SCSW_ACTL_SUSPENDED))
> >  }
> 
> I'd split that impenetrable boolean expression up.
> 
> I think this is equivalent:
> 	if (!scsw->tm.fctl)
> 		return 0;
> 	if (!(scsw->tm.stctl & SCSW_STCTL_STATUS_PEND))
> 		return 0;
> 	if (!(scsw->tm.stctl & SCSW_STCTL_INTER_STATUS))
> 		return 1
> 	if (scsw->tm.actl & SCSW_ACTL_SUSPENDED)
> 		return 1;
> 	return 0;
> 
> The generated code could even be the same.

Yes, we had the very same discussion here:
https://lore.kernel.org/linux-s390/20210820025159.11914-1-jing.yangyang@zte.com.cn/

Where the outcome also was that it doesn't make sense to replace one
unreadable version with another unreadable version just to get rid of
a warning.

Haowen, could you please resend with a proper readable version, or
alternatively, Vineeth, could you address this please, so this doesn't
come up again?

Thanks!