Subject: Re: linux-next: build failure after merge of the akpm-current tree

From: Russell King <[email-masked]>
Date: Mon, 6 Jan 2014 17:28:49 +0000

On Mon, Jan 06, 2014 at 08:07:58PM +1100, Stephen Rothwell wrote:
> Hi Andrew,
> 
> After merging the akpm-current tree, today's linux-next build (arm
> multi_v7_defconfig) failed like this:
> 
> arch/arm/mm/init.c:199:13: error: conflicting types for 'arm_dma_zone_size'
> include/linux/bootmem.h:259:11: note: previous declaration of 'arm_dma_zone_size' was here
> 
> Caused by commit a3ae9362fafe ("mm/memblock: add memblock memory
> allocation apis").
> 
> For this build, BOOTMEM_LOW_LIMIT is defined as __pa(MAX_DMA_ADDRESS) and
> MAX_DMA_ADDRESS is defined as:
> 
> #define MAX_DMA_ADDRESS ({ \
>         extern unsigned long arm_dma_zone_size; \
>         arm_dma_zone_size ? \
>                 (PAGE_OFFSET + arm_dma_zone_size) : 0xffffffffUL; })
> 
> and in arch/arm/mm/init.c, arm_dma_zone_size is declared as:
> 
> phys_addr_t arm_dma_zone_size __read_mostly;
> 
> Urk!  :-(
> 
> OK, so commit 364230b995214 ("ARM: use phys_addr_t for DMA zone sizes")
> changed the definition of arm_dma_zone_size except it missed the one in
> arch/arm/include/asm/dma.h.
> 
> I have applied this merge fix patch for today:

There's more here than just this change required here.  We also need to
limit it if PAGE_OFFSET + arm_dma_zone_size is greater than 4GB, as
MAX_DMA_ADDRESS is a virtual address - we really don't want the 32-bit
value of this wrapping.

Exactly how we go about this, I'm not sure at the moment, but maybe
something like this:

#define MAX_DMA_ADDRESS ({ \
        extern phys_addr_t arm_dma_zone_size; \
        arm_dma_zone_size && arm_dma_zone_size < (0x10000000 - PAGE_OFFSET) ? \
                (PAGE_OFFSET + arm_dma_zone_size) : 0xffffffffUL; })

-- 
Russell King
ARM architecture Linux Kernel maintainer