recent ARM Erratas 742231 & 742230 broken.

[Will Deacon]

Hey Linus,

> 2010/10/20 Will Deacon <will.deacon at arm.com>:
> 
> > The diagnostic register is only writable from secure mode so you'll need to
> > look at what these patches do (they perform simple read-modify-writes) and
> > incorporate that code into your secure software.
> > (...)
> > I doubt that your secure monitor exposes the diagnostic register through an
> > SMC interface so you'll need to change the secure boot code to enable these
> > workarounds when the system comes out of reset.
> 
> These SMC:s (System Management Call?) are getting hairier now.

Secure Monitor Call :)

What I was eluding to above is that exposing things like the diagnostic
register via an SMC is a *really* bad idea.  It's much better to set /clear
any necessary bits in the secure boot code and then be done with it.
If that's not possible, you could have a bunch of per-erratum SMCs
but if you can modify the monitor in such a way then you should be able
to modify the boot code too.
 
> Can't you add an abstraction for the stuff we need to poke into
> diagnostics registers, enabling platform-specific overrides, like
> we do for l2x0 in mm/cache-l2x0.c?

I think Russell addressed this point.

Cheers,

Will