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Date:	Mon, 20 Oct 2014 15:50:27 +0200
From:	Stefan Hengelein <>
To:	Marek Szyprowski <>
	Valentin Rothberg <>
Subject: Re: [PATCH] arm: dma-mapping: fix compilation error when CONFIG_MMU
 is not present


arch/arm/mm/dma-mapping.c: In function ‘__atomic_get_pages’:
arch/arm/mm/dma-mapping.c:1265:31: error: ‘atomic_pool’ undeclared
(first use in this function)

arch/arm/mm/dma-mapping.c: In function ‘__iommu_get_pages’:
arch/arm/mm/dma-mapping.c:1275:2: error: implicit declaration of
function ‘__in_atomic_pool’ [-Werror=implicit-function-declaration]

arch/arm/mm/dma-mapping.c: In function ‘__iommu_alloc_remap’:
arch/arm/mm/dma-mapping.c:1200:4: error: ‘VM_ARM_DMA_CONSISTENT’
undeclared (first use in this function)
arch/arm/mm/dma-mapping.c:1200:4: note: each undeclared identifier is
reported only once for each function it appears in

arch/arm/mm/dma-mapping.c: In function ‘__iommu_get_pages’:
arch/arm/mm/dma-mapping.c:1282:29: error: ‘VM_ARM_DMA_CONSISTENT’
undeclared (first use in this function)
arch/arm/mm/dma-mapping.c: In function ‘arm_iommu_free_attrs’:
arch/arm/mm/dma-mapping.c:1411:4: error: ‘VM_ARM_DMA_CONSISTENT’
undeclared (first use in this function)

i've attached a configuration where it happens.
when you place the configuration in your tree and compile the file,
the errors should show up.

However, within the configuration CONFIG_ARM_DMA_USE_IOMMU is defined
and CONFIG_MMU is not. AFAIUI, if both should be enabled together, it
should be mapped in Kconfig somewhere, right?

Best Regards,

2014-10-20 9:42 GMT+02:00 Marek Szyprowski <>:
> Hello,
> On 2014-10-19 17:59, Stefan Hengelein wrote:
>> When CONFIG_MMU is not present, the variable 'atomic_pool' and the
>> function '__in_atomic_pool' are undeclared but used in part of the
>> code. Therefore, the compilation breaks.
>> Now, they are defined to dummy values when CONFIG_MMU is undefined.
>> This error was found with vampyr.
> Frankly, those variables are used only when CONFIG_MMU or
> CONFIG_ARM_DMA_USE_IOMMU are set. The latter imho makes only sense
> together with CONFIG_MMU, so the issue reported here doesn't really
> happen in real world.
>> Signed-off-by: Stefan Hengelein <>
>> ---
>>   arch/arm/mm/dma-mapping.c | 2 ++
>>   1 file changed, 2 insertions(+)
>> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
>> index c245d90..7d04cf7 100644
>> --- a/arch/arm/mm/dma-mapping.c
>> +++ b/arch/arm/mm/dma-mapping.c
>> @@ -573,12 +573,14 @@ static inline pgprot_t __get_dma_pgprot(struct
>> dma_attrs *attrs, pgprot_t prot)
>>   #else /* !CONFIG_MMU */
>>     #define nommu() 1
>> +#define atomic_pool 0
>>     #define __get_dma_pgprot(attrs, prot)       __pgprot(0)
>>   #define __alloc_remap_buffer(dev, size, gfp, prot, ret, c)    NULL
>>   #define __alloc_from_pool(size, ret_page)                     NULL
>>   #define __alloc_from_contiguous(dev, size, prot, ret, c)      NULL
>>   #define __free_from_pool(cpu_addr, size)                      0
>> +#define __in_atomic_pool(start, size)                          0
>>   #define __free_from_contiguous(dev, page, cpu_addr, size)     do { }
>> while (0)
>>   #define __dma_free_remap(cpu_addr, size)                      do { }
>> while (0)
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland

Download attachment ".config" of type "application/octet-stream" (145089 bytes)

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