Re: [Qemu-devel] [RFC] powernv: CPU compatibility modes don't make sense for powernv

[Greg Kurz <groug@kaod.org>]

On Fri, 28 Oct 2016 13:05:01 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> powernv has some code (derived from the spapr equivalent) used in device
> tree generation which depends on the CPU's compatibility mode / logical
> PVR.  However, compatibility modes don't make sense on powernv - at least
> not as a property controlled by the host - because the guest in powernv
> has full hypervisor level access to the virtual system, and so owns the
> PCR (Processor Compatibility Register) which implements compatiblity modes.
> 

This makes a lot of sense indeed.

> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  hw/ppc/pnv.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> Hi Cédric, I'd appreciate it if you can double check my reasoning
> here.  This patch gets powernv out of the way of a bunch of
> compatibility mode cleanups I have in the works.
> 
> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> index 82276e0..6af3424 100644
> --- a/hw/ppc/pnv.c
> +++ b/hw/ppc/pnv.c
> @@ -110,7 +110,7 @@ static void powernv_create_core_node(PnvChip *chip, PnvCore *pc, void *fdt)
>      CPUState *cs = CPU(DEVICE(pc->threads));
>      DeviceClass *dc = DEVICE_GET_CLASS(cs);
>      PowerPCCPU *cpu = POWERPC_CPU(cs);
> -    int smt_threads = ppc_get_compat_smt_threads(cpu);
> +    int smt_threads = CPU_CORE(pc)->nr_threads;

Not speaking of the PCR, this has also another effect since 
ppc_get_compat_smt_threads() also take the KVM smt capability
into account:

    int ret = MIN(cs->nr_threads, kvmppc_smt_threads());

Shouldn't you do the same here ?

>      CPUPPCState *env = &cpu->env;
>      PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cs);
>      uint32_t servers_prop[smt_threads];
> @@ -206,10 +206,6 @@ static void powernv_create_core_node(PnvChip *chip, PnvCore *pc, void *fdt)
>      _FDT((fdt_setprop(fdt, offset, "ibm,pa-features",
>                         pa_features, sizeof(pa_features))));
>  
> -    if (cpu->cpu_version) {
> -        _FDT((fdt_setprop_cell(fdt, offset, "cpu-version", cpu->cpu_version)));
> -    }
> -
>      /* Build interrupt servers properties */
>      for (i = 0; i < smt_threads; i++) {
>          servers_prop[i] = cpu_to_be32(pc->pir + i);