Re: [PATCH 0/2] MIPS: Memory setup tweaks

[James Hogan <james.hogan@imgtec.com>]

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On Tue, Aug 16, 2016 at 05:36:07PM +0200, Ralf Baechle wrote:
> On Tue, Aug 09, 2016 at 01:21:47PM +0100, James Hogan wrote:
> 
> > Here are a couple of tweaks for MIPS memory setup, primarily in order to
> > handle memory which extends right up to the end of physical memory on
> > 32-bit systems with 32-bit phys_addr_t. More specifically we omit the
> > final page of physical memory to avoid the overflow (see patch 1 for
> > details).
> > 
> > Patch 2 improves the rounding in the MAAR setup, so as to include the
> > first full page of an already aligned region, and to avoid a BUG_ON for
> > regions with non 64-KByte aligned end addresses (which I happened to hit
> > while working on a different version of patch 1 which wasn't correctly
> > merging the kernel data section into the main RAM region).
> 
> There's a DMA issue with one of the system controllers on Malta which
> afair only affects one endianess and can be worked around by not using
> the last bit of memory. That isn't the only platform having such issues
> I've seen and debugging has always been very painful so I'm wondering
> if as a general precaution we should just leave the last page of memory
> unused.

If I understand you right, I think thats pretty much what patch 1 does,
or rather it allows such a region to be created but reduces the length
so it doesn't quite reach the end, I suppose assuming it will get
rounded down to a page boundary.

Cheers
James

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