linux-kernel - Re: drivers/mtd/maps/physmap-bt1-rom.c:78:18: sparse: sparse: cast removes address space '__iomem' of expression

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Message-ID: <20201112152739.r4673zyeixkcwukx@mobilestation>
Date:   Thu, 12 Nov 2020 18:27:39 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Vignesh Raghavendra <vigneshr@...com>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        <linux-mtd@...ts.infradead.org>, <kbuild-all@...ts.01.org>,
        kernel test robot <lkp@...el.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: drivers/mtd/maps/physmap-bt1-rom.c:78:18: sparse: sparse: cast
 removes address space '__iomem' of expression

Hello Vignesh

On Thu, Nov 12, 2020 at 08:30:42PM +0530, Vignesh Raghavendra wrote:
> 
> 
> On 11/12/20 1:57 PM, Miquel Raynal wrote:
> > Hi Sergey,
> > 
> > Serge Semin <Sergey.Semin@...kalelectronics.ru> wrote on Wed, 11 Nov
> > 2020 22:22:59 +0300:
> > 
> >> On Tue, Nov 10, 2020 at 04:35:56PM +0100, Miquel Raynal wrote:
> >>> Hi Serge,
> >>>
> >>> Serge Semin <Sergey.Semin@...kalelectronics.ru> wrote on Tue, 10 Nov
> >>> 2020 14:38:27 +0300:
> >>>   
> >>>> Hello Miquel,
> >>>>
> >>>> A situation noted by the warning below won't cause any problem because
> >>>> the casting is done to a non-dereferenced variable. It is utilized
> >>>> as a pointer bias later in that function. Shall we just ignore the
> >>>> warning or still fix it somehow?  
> >>>   
> >>
> >>> Do you think the cast to a !__iomem value is mandatory here?  
> >>
> >> It's not mandatory to have the casting with no __iomem, but wouldn't
> >> doing like this:
> >> + 	shift = (ssize_t __iomem)src & 0x3;
> >> be looking weird? Really, is there a good way to somehow extract the first
> >> two bits of a __iomem pointer without getting the sparse warning?
> > 
> > I asked around me, what about trying uintptr_t?
> > 
> 

> One more way is to use __force to tell sparse that this casting is
> intentional:
> 
>        shift = (__force ssize_t)src & 0x3;

Oh, great! That solution is actually much better than using some
currently unexplained sparse peculiarity! I was thinking about applying
some other attribute, but __force just didn't come to my mind. Thank
you very much for the suggestion. I'll post the fix with the solution
suggested by you.

-Sergey

> 
> 
> > Thanks,
> > Miquèl
> > 
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/
> > 

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