Re: [PATCH] of: Allow mem_reserve of memory with a base address of zero

On Wed, 6 Aug 2014 17:02:44 -0500, Rob Herring [off-list ref] wrote:

On Wed, Aug 6, 2014 at 3:30 PM, Al Cooper [off-list ref] wrote:

quoted

__reserved_mem_reserve_reg() won't reserve memory if the base address
is zero. This change removes the check for a base address of zero and
allows it to be reserved.

Allowing the first 4K of memory to be reserved will help solve a
problem on some ARM systems where the the first 16K of memory is
unused and becomes allocable memory. This will prevent this memory
from being used for DMA by drivers like the USB OHCI driver which
consider a physical address of zero to be illegal.

OHCI driver or hardware? I agree with the change, but really think
this should be fixed in the driver in the former case or a property of
the OHCI node in the latter.

I'm not hard and fast on that. I don't think it is unreasonable to
reserve the base of memory as the platform level if there is a bug
causing DMA to fail at that address.

If this is a common problem (and not merely a few boards) then I agree.
Fixing it this way is just asking for the same problem to show up again
and again on new boards that haven't explicitly reserved the memory.

g.

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