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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Date:   Thu, 12 Nov 2020 20:30:42 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>
CC:     <linux-mtd@...ts.infradead.org>, <kbuild-all@...ts.01.org>,
        kernel test robot <lkp@...el.com>,
        Serge Semin <fancer.lancer@...il.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

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;

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

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