Memory allocation problem using GFP_COMP?

Memory allocation problem using GFP_COMP?

[Breton M. Saunders]

Folks,

  I've got a problem in allocating DMA memory on ARM for a driver on 2.6.19:

  The function snd_malloc_dev_pages requests memory using the 
dma_alloc_coherent function on line 222 of sound/core/memalloc.c.  This 
allocation is done with the bit __GFP_COMP set, which throws an oops in 
the ARM memory allocation __dma_alloc.  My understanding from speaking 
with Russell King is that __GFP_COMP should never be specified when 
calling dma_alloc_coherent.

  Is this a bug?

    Cheers,

       -Brett


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Re: Memory allocation problem using GFP_COMP?

[Takashi Iwai]

At Fri, 12 Jan 2007 17:37:05 +0000,
Breton M. Saunders wrote:
> 
> Folks,
> 
>   I've got a problem in allocating DMA memory on ARM for a driver on 2.6.19:
> 
>   The function snd_malloc_dev_pages requests memory using the 
> dma_alloc_coherent function on line 222 of sound/core/memalloc.c.  This 
> allocation is done with the bit __GFP_COMP set, which throws an oops in 
> the ARM memory allocation __dma_alloc.  My understanding from speaking 
> with Russell King is that __GFP_COMP should never be specified when 
> calling dma_alloc_coherent.
> 
>   Is this a bug?

Well, this is really a long-standing problem.  __GFP_COMP is required
for other architectures, but not for ARM.  Also, the mmap should be
done dma_mmap_coherent() on ARM instead of vm nopage callback.

In short, we need:
- an offical allocation method of mmappable coherent dma memory
and
- an API for mmapping such area.


Takashi

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