linux-kernel - Re: [PATCH] media: atomisp: silence "dubious: !x

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Message-ID: <20210418011552.GA4023@ashish-NUC8i5BEH>
Date:   Sun, 18 Apr 2021 06:45:52 +0530
From:   Ashish Kalra <eashishkalra@...il.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Mauro Carvalho Chehab' <mchehab@...nel.org>,
        Ashish Kalra <eashishkalra@...il.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: atomisp: silence "dubious: !x | !y" warning

On Sat, Apr 17, 2021 at 09:31:32PM +0000, David Laight wrote:
> From: Mauro Carvalho Chehab
> > Sent: 17 April 2021 19:56
> > 
> > Em Sat, 17 Apr 2021 21:06:27 +0530
> > Ashish Kalra <eashishkalra@...il.com> escreveu:
> > 
> > > Upon running sparse, "warning: dubious: !x | !y" is brought to notice
> > > for this file.  Logical and bitwise OR are basically the same in this
> > > context so it doesn't cause a runtime bug.  But let's change it to
> > > logical OR to make it cleaner and silence the Sparse warning.
> 
> The old code is very likely to by slightly more efficient.
> 
> It may not matter here, but it might in a really hot path.
> 
> Since !x | !y and !x || !y always have the same value
> why is sparse complaining at all.
> 
> 	David
This warning is coming from sparse as per below explanation

As the name suggests, a "bitwise" expression is one that is restricted to
only a certain "bitwise" operations that make sense within that class. In
particular, you can't mix a "bitwise" class with a normal integer
expression
Warning:
int __bitwise i;
int __bitwise j;
the two variables "i" and "j" are _not_ compatible, simply because they
were declared separately, while in the case of
	int __bitwise i, j;
they _are_ compatible.

https://yarchive.net/comp/linux/sparse.html
> 
> > >
> > > Signed-off-by: Ashish Kalra <eashishkalra@...il.com>
> > > ---
> > >  .../media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c    | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c
> > b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c
> > > index 358cb7d2cd4c..3b850bb2d39d 100644
> > > --- a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c
> > > +++ b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c
> > > @@ -58,7 +58,7 @@ sh_css_vf_downscale_log2(
> > >  	unsigned int ds_log2 = 0;
> > >  	unsigned int out_width;
> > >
> > > -	if ((!out_info) | (!vf_info))
> > > +	if ((!out_info) || (!vf_info))
> > 
> > 
> > While here, please get rid of the unneeded parenthesis:
> > 
> > 	if (!out_info || !vf_info)
> > 
> > 
> > >  		return -EINVAL;
> > >
> > >  	out_width = out_info->res.width;
> > 
> > 
> > 
> > Thanks,
> > Mauro
> 
> -
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