[RFC PATCH 3/3] pstore/ram: avoid atomic accesses for ioremapped regions

[Colin Cross]

On Tue, Apr 9, 2013 at 8:08 PM, Rob Herring <robherring2 at gmail.com> wrote:
> From: Rob Herring <rob.herring at calxeda.com>
>
> For persistent RAM outside of main memory, the memory may have limitations
> on supported accesses. For internal RAM on highbank platform exclusive
> accesses are not supported and will hang the system. So atomic_cmpxchg
> cannot be used. This commit uses spinlock protection for buffer size and
> start updates on ioremapped regions instead.

I used atomics in persistent_ram to support persistent ftrace, which
now exists as PSTORE_FTRACE.  At some point during development I had
trouble with recursive tracing causing an infinite loop, so you may
want to test that calling out to spinlock functions with PSTORE_FTRACE
turned on and enabled doesn't cause a problem.