[Skiboot] Skiboot upgrade needed for VAS/NX

[Sukadev Bhattiprolu]

Oliver [oohall at gmail.com] wrote:
> On Wed, Sep 6, 2017 at 4:10 AM, Sukadev Bhattiprolu
> <sukadev at linux.vnet.ibm.com> wrote:
> >
> > Please note that if you are testing recent powerpc/next code with CONFIG_VAS
> > enabled on a DD2 system, please upgrade to latest skiboot (5.8).
> >
> > Otherwise you will run into a machine check like this one reported by
> > Nick Piggin.
> 
> 
> What's the underlying issue here? We're supposed to avoid this sort of
> issue though compat strings, etc. What bug is fixed in 5.8 that solves
> this?
> 

DD2 hardware required setting three new enable bits, without which a write
to the VAS registers results in a machine check. Following commit fixed
that. DD1 did not need these to be set.

	commit b503dcf
	Author: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
	Date:   Thu Aug 17 17:50:24 2017 -0700

	    vas: Set mmio enable bits in DD2
	    
	    POWER9 DD2 added some new "enable" bits that must be set for VAS to
	    work. These bits were unused in DD1.

There was also a bug in the setting of FIRs which results in the checkstop.
for potentially recoverable errors. That was fixed by:

	commit a5c1240
	Author: Michael Neuling <mikey at neuling.org>
	Date:   Mon Aug 21 17:16:06 2017 +1000

	    vas: Set FIRs according to workbook

Both fixes are in 5.8 skiboot.

All these registers are set using SCOM so they are initialized in skiboot
rather than by the kernel. Are there ways we can fix the kernel without
requiring a skiboot change?

Sukadev