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

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Vignesh Raghavendra <vigneshr@ti.com>,
	Serge Semin <fancer.lancer@gmail.com>,
	<linux-mtd@lists.infradead.org>, <kbuild-all@lists.01.org>,
	kernel test robot <lkp@intel.com>, <linux-kernel@vger.kernel.org>
Subject: Re: drivers/mtd/maps/physmap-bt1-rom.c:78:18: sparse: sparse: cast removes address space '__iomem' of expression
Date: Thu, 12 Nov 2020 16:43:01 +0100	[thread overview]
Message-ID: <20201112164301.60032276@xps13> (raw)
In-Reply-To: <20201112152739.r4673zyeixkcwukx@mobilestation>

Hi Serge,

Serge Semin <Sergey.Semin@baikalelectronics.ru> wrote on Thu, 12 Nov
2020 18:27:39 +0300:

> 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@baikalelectronics.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@baikalelectronics.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.

Is the ssize_t cast the right one btw? I would definitely prefer an
unsigned type here.

Thanks,
Miquèl