Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx> writes: > On Tue, 2016-11-08 at 19:21 +1100, Michael Ellerman wrote: >> Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx> 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 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. cheers -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
