On Sun, 29 May 2011, Russell King - ARM Linux wrote:

We might as well enable CONFIG_ZONE_DMA for everything if that's what
you're proposing, because it's not just this driver which will be affected.

I'd certainly suggest at least defaulting it to on for arm if you're going 
to be using GFP_DMA in drivers.

And as soon as we do that, we completely lose the warnings that stuff
needs fixing.

That's because nothing needs fixing at that point, the page allocator is 
guaranteed to return lowmem if GFP_DMA is passed and CONFIG_ZONE_DMA is 
enabled, or NULL.  Whether GFP_DMA is correct in the memory allocator is a 
different subject, but those types of audits can easily be done on the 
source code.  In my opinion, we should be doing "select ZONE_DMA" on any 
Kconfig option that builds a driver that unconditionally uses GFP_DMA.

The current behavior exists so that the admin reports the error here so it 
can get fixed up (either by finding that GFP_DMA is unnecessary, selective 
depending on the particular hardware, or modifying the Kconfig) and can 
workaround the problem by forcing CONFIG_ZONE_DMA.