[PATCH] arm: omap4: Fix omap_barriers_init for generic ioremap changes

[Russell King - ARM Linux]

On Thu, Jan 12, 2012 at 10:42:57AM -0800, Tony Lindgren wrote:
> Commit 73829af71fdb8655e7ba4b5a2a6612ad34a75a11
> (Merge branch 'vmalloc' of git://git.linaro.org/people/nico/linux
> into devel-stable) merged generic ioremap changes.
> 
> Commit 137d105d50f6e6c373c1aa759f59045e6239cf66
> (ARM: OMAP4: Fix errata i688 with MPU interconnect barriers)
> added a workaround for omap4.
> 
> In order for the errata to work, we now need the following
> patch or else we'll get:
> 
> kernel BUG at mm/vmalloc.c:1134!

Oh my, I've just read this, and I'm extremely annoyed that this even hit
mainline in the first place.  It's utter crap.

It's trying to use memblock to allocate memory _AFTER_ that memory has
been passed on from memblock's control to other allocators.  Calling
memblock_alloc() at *any* initcall is Bad News (it _may_ appear to work
but there's no way for memblock_alloc to tell anything else that the
memory is being re-used.)

Calling it and then trying to reserve it at ->map_io time is also Bad
News - the memory at that point has already been mapped, and if you're
expecting to be able to remap it with different attributes, you're going
to double-map it with differing attributes.  You lose.

Not only that, but it's an abuse of the various callback functions into
machine code.  Don't do it.

By all means, allocate the memory via memblock, but do it in the ->reserve
callback.  It's *exactly* what that callback is there for.  The map it in
the ->map_io callback.

Don't try to be clever and abuse these callbacks.  They aren't named just
for fun and my delectation.  They have *specific* purposes.  Stick to
those purposes in them and don't try to be clever, or you'll be moaned at.

So, NAK.  NAK for the original patch too.  Do it properly.