Subject: Re: [PATCH V3 1/2] powerpc: Define new ISA v3.00 logical PVR value and PCR register value

From: Suraj Jitindar Singh <[email-masked]>
Date: Fri, 11 Nov 2016 17:11:53 +1100

On Thu, 2016-11-10 at 21:36 +1100, Michael Ellerman wrote:
> Suraj Jitindar Singh <[email-masked]> writes:
> 
> > 
> > On Tue, 2016-11-08 at 19:21 +1100, Michael Ellerman wrote:
> > > 
> > > Suraj Jitindar Singh <[email-masked]> 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