On Thu, 2016-11-10 at 21:36 +1100, Michael Ellerman wrote:
> Suraj Jitindar Singh <sjitindarsi...@gmail.com> writes:
>
> >
> > On Tue, 2016-11-08 at 19:21 +1100, Michael Ellerman wrote:
> > >
> > > Suraj Jitindar Singh <sjitindarsi...@gmail.com> writes:
> > >
> > > >
> > > >
> > > > ISA 3.00 adds the logical PVR value 0x0f000005, so add a
> > > > definition
> > > > for
> > > > this.
> > > >
> > > > Define PCR_ARCH_207 to reflect ISA 2.07 compatibility mode in
> > > > the
> > > > processor
> > > > compatibility register (PCR). Also define a dummy ISA 3.00
> > > > compatibility
> > > > mode PCR_ARCH_300 to be used in the next patch to help with
> > > > determining the
> > > > PCR value.
> > > What's "dummy" about the PCR value?
> >
> > Then next patch needs some PCR bit to specify that we want to
> > emulate
> > v3.00 and/or that the host can emulate v3.00 to follow the pattern
> > used
> > to determine that the host is capable of emulating the given compat
> > level and for determining which PCR bits to set. But no such bit is
> > defined for V3.00 compat mode yet so a "dummy" one is used to
> > represent
> > this even though it's never defined in the ISA.
> > >
> > >
> > > AFAICS that value is reserved in the ISA.
> >
> > Yes it is a reserved bit in the PCR register but it will never
> > actually
> > be set, it will always be cleared by "host_pcr_bit -
> > guest_pcr_bit;"
> >
> > >
> > >
> > > Are we assuming/hoping that ISA 4.0 will use 0x10 to mean ISA 3.0
> > > ?
> >
> > Basically yes, and although I know nothing's given, it would follow
> > the
> > current pattern for whatever the next ISA version is to use 0x10 to
> > mean V3.00 compat mode. Otherwise this will need to be updated at
> > some
> > point when that's released... In fact if the compat bits are no
> > longer
> > sequential this will need rewriting.
>
> OK thanks.
>
> Please send a v4 with that detail in a comment and a better
> explanation
> in the change log.
>
> I think a block comment before the #define would be best, ie.
> something
Will do and send a V4
> like:
>
> #define PCR_ARCH_207 0x8 /* Architecture 2.07
> */
>
> /*
> * All that helpful detail from above ...
> */
> #define PCR_ARCH_300 0x10
>
>
> We should also ask if we can get 0x10 reserved in the ISA to mean
> 3.00.
Probably a good idea, might ask you about the process for this on
Monday...
>
> cheers
