ARM diagnostic register across suspend/resume

[Russell King - ARM Linux]

On Tue, Jun 17, 2014 at 10:57:29AM +0100, Will Deacon wrote:
> On Tue, Jun 17, 2014 at 09:31:18AM +0100, Shawn Guo wrote:
> > Hi Will, Catalin,
> > 
> > The CP15 diagnostic register holds some bits for ARM errata workaround.
> > Since core gets power gated across suspend/resume cycle, these bits will
> > get lost along the way.  Is it okay for errata workaround to continue
> > working after suspend, or do we have to save/restore diagnostic register
> > to keep workaround effective?
> 
> I'm not sure that saving/restoring the diagnostic register on A9 actually
> works at all (I seem to remember some bits always read as zero?).

If that's true, then we have a problem.  We always read-modify-write
this register when enabling work-arounds.  If it always reads as
zero, then enabling a subsequent work-around will disable the
previous work-around.

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