Re: [Qemu-devel] [PATCH v8 07/13] target-arm: Make PMCEID[01]_EL0 64 bit registers, add PMCEID[23]

[Richard Henderson <richard.henderson@linaro.org>]

On 12/3/18 4:19 PM, Peter Maydell wrote:
> On Mon, 3 Dec 2018 at 20:45, Aaron Lindsay <aaron@os.amperecomputing.com> wrote:
>>
>> On Nov 30 16:10, Peter Maydell wrote:
>>> PMCEID2 and PMCEID3 are only defined from ARMv8.1; before that they
>>> are UNDEFINED. So these registers need to be only defined if a
>>> suitable feature bit or ID register field check passes.
>>
>> It looks like we don't currently support any ARMv8.1+ CPUs and don't
>> have an entry in the `arm_features` enum for it. I'll plan to add
>> ARM_FEATURE_V81 and make defining these registers depend on it, assuming
>> any future CPUs supporting it will use that, unless you feel I should do
>> something different.
> 
> I think that the idea going forward is to prefer an ID
> register check of some kind -- Richard ?

Yes.  It would appear that this feature should be controlled by
ID_DFR0.PerfMon.  So,

  if (FIELD_EX32(cpu->id_dfr0, ID_DFR0, PERFMON) >= 4)

once the appropriate FIELDs are added to cpu.h.

Since this test is not used within translate*.c, there is no need to move
id_dfr* into ARMISARegisters.  Since these are only aliases, they do not affect
migration, and so do not (yet) need to be filled in by kvm.


r~