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

[Shilimkar, Santosh]

On Thu, Jan 12, 2012 at 9:11 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Thu, Jan 12, 2012 at 08:04:43PM +0000, Russell King - ARM Linux wrote:
>> 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.
>
> It seems I missed this detail when I quickly read through the original
> patch last September, which is rather unfortunate.
>
> That doesn't stop this being completely the wrong approach though - and
> being very very broken as it currently stands.

May be I have missed you point but I thought below
should remove the initial mapping.

memblock_free(paddr, size);
memblock_remove(paddr, size);

This patch actually got under various versions. Indeed the
first version did implement the ->reserve callback method
but then it kept changing and you might have lost track of it.

Regards
Santosh