Re: [BK-2.5] Update the generic DMA API to take GFP_ flags on

[Russell King <rmk@arm.linux.org.uk>]

On Tue, Jan 14, 2003 at 07:30:23AM -0800, David S. Miller wrote:
>    From: James Bottomley <James.Bottomley@steeleye.com>
>    Date: Tue, 14 Jan 2003 10:30:15 -0500
> 
>    A GFP_KERNEL request is safely implemented as GFP_ATOMIC as long as the caller 
>    checks return for NULL.  for dma_alloc_coherent return checking is a 
>    requirement because the system may return NULL anyway if it is out of mappings 
>    even with a GFP_KERNEL flag.
>    
> Now what about the corollary, a platform that needs
> to sleep to setup the cpu mapings in a race-free manner?
> 
> It could not ever honor GFP_ATOMIC in that case.

That got solved in recent 2.5, albiet with limit of 2MB of consistent /
coherent allocations at any one time.  We return NULL if we run out of
space, and _all_ callers must check the return code of
pci_alloc_consistent and/or dma_alloc_coherent no matter what flags they
pass in.

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html