On Fri, Jun 10, 2011 at 03:16:00PM -0700, David Rientjes wrote:

On Fri, 10 Jun 2011, Russell King - ARM Linux wrote:

quoted

quoted

We're talking about two different things.  Linus is saying that if GFP_DMA 
should be a no-op if the hardware doesn't require DMA memory because the 
kernel was correctly compiled without CONFIG_ZONE_DMA.  I'm asking about a 
kernel that was incorrectly compiled without CONFIG_ZONE_DMA and now we're 
returning memory from anywhere even though we actually require GFP_DMA.

How do you distinguish between the two states?  Answer: you can't.

By my warning which says "enable CONFIG_ZONE_DMA _if_ needed."  The 
alternative is to silently return memory from anywhere, which is what the 
page allocator does now, which doesn't seem very user friendly when the 
device randomly works depending on the chance it was actually allocated 
from the DMA mask.  If it actually wants DMA and the kernel is compiled 
incorrectly, then I think a single line in the kernel log would be nice to 
point them in the right direction.  Users who disable the option usually 
know what they're doing (it's only allowed for CONFIG_EXPERT on x86, for 
example), so I don't think they'll mind the notification and choose to 
ignore it.

So those platforms which don't have a DMA zone, don't have any problems
with DMA, yet want to use the very same driver which does have a problem
on ISA hardware have to also put up with a useless notification that
their kernel might be broken?

Are you offering to participate on other architectures mailing lists to
answer all the resulting queries?

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