linux-kernel - Re: [PATCH 3/3] dma-contiguous: Type cast MAX

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Message-ID: <cb6b039a-5a8f-b2c4-2c9e-bcd973ba6232@arm.com>
Date:   Fri, 12 Feb 2021 12:49:28 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, akpm@...ux-foundation.org,
        will@...nel.org, Robin Murphy <robin.murphy@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        David Hildenbrand <david@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] dma-contiguous: Type cast MAX_ORDER as unsigned int



On 2/11/21 1:34 PM, Christoph Hellwig wrote:
> On Thu, Feb 11, 2021 at 11:52:11AM +0530, Anshuman Khandual wrote:
>> Type cast MAX_ORDER as unsigned int to fix the following build warning.
>>
>> In file included from ./include/linux/kernel.h:14,
>>                  from ./include/asm-generic/bug.h:20,
>>                  from ./arch/arm64/include/asm/bug.h:26,
>>                  from ./include/linux/bug.h:5,
>>                  from ./include/linux/mmdebug.h:5,
>>                  from ./arch/arm64/include/asm/memory.h:166,
>>                  from ./arch/arm64/include/asm/page.h:42,
>>                  from kernel/dma/contiguous.c:46:
>> kernel/dma/contiguous.c: In function ‘rmem_cma_setup’:
>> ./include/linux/minmax.h:18:28: warning: comparison of distinct pointer
>> types lacks a cast
>>   (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
>>                             ^~
>> ./include/linux/minmax.h:32:4: note: in expansion of macro ‘__typecheck’
>>    (__typecheck(x, y) && __no_side_effects(x, y))
>>     ^~~~~~~~~~~
>> ./include/linux/minmax.h:42:24: note: in expansion of macro ‘__safe_cmp’
>>   __builtin_choose_expr(__safe_cmp(x, y), \
>>                         ^~~~~~~~~~
>> ./include/linux/minmax.h:58:19: note: in expansion of macro
>> ‘__careful_cmp’
>>  #define max(x, y) __careful_cmp(x, y, >)
>>                    ^~~~~~~~~~~~~
>> kernel/dma/contiguous.c:402:35: note: in expansion of macro ‘max’
>>   phys_addr_t align = PAGE_SIZE << max(MAX_ORDER - 1, pageblock_order);
>>
>> Cc: Christoph Hellwig <hch@....de>
>> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
>> Cc: Robin Murphy <robin.murphy@....com>
>> Cc: iommu@...ts.linux-foundation.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>  kernel/dma/contiguous.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
>> index 3d63d91cba5c..1c2782349d71 100644
>> --- a/kernel/dma/contiguous.c
>> +++ b/kernel/dma/contiguous.c
>> @@ -399,7 +399,7 @@ static const struct reserved_mem_ops rmem_cma_ops = {
>>  
>>  static int __init rmem_cma_setup(struct reserved_mem *rmem)
>>  {
>> -	phys_addr_t align = PAGE_SIZE << max(MAX_ORDER - 1, pageblock_order);
>> +	phys_addr_t align = PAGE_SIZE << max((unsigned int)MAX_ORDER - 1, pageblock_order);
> 
> MAX_ORDER and pageblock_order should be the same type.  So either fix

Right.

> MAX_ORDER to be an unsigned constant, which would be fundamentally
> the right thing to do but might cause some fallout, or turn
> pageblock_order into an int, which is probably much either as the stub
> define of it already has an integer type derived from MAX_ORDER as well.

Right, will change pageblock_order as 'int' which would be easier.