Re: [Qemu-ppc] [QEMU-PPC] [PATCH 4/4] target/ppc/spapr: Enable the large decrementer by default on POWER9

[David Gibson]

On Tue, Feb 26, 2019 at 02:05:31PM +1100, Suraj Jitindar Singh wrote:
> Enable the large decrementer by default on POWER9 cpu models. The
> default value applied is that provided in the cpu class.
> 
> Signed-off-by: Suraj Jitindar Singh <address@hidden>
> ---
>  hw/ppc/spapr_caps.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index e07568fb94..f48aa367e3 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -566,11 +566,18 @@ sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
>  static sPAPRCapabilities default_caps_with_cpu(sPAPRMachineState *spapr,
>                                                 const char *cputype)
>  {
> +    PowerPCCPUClass *pcc = POWERPC_CPU_CLASS(object_class_by_name(cputype));
>      sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(spapr);
>      sPAPRCapabilities caps;
>  
>      caps = smc->default_caps;
>  
> +    caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = pcc->hdecr_bits;

So, the rule with default_caps_with_cpu() is that it can reduce the
value from the machine-global default, but never increase it (because
that could change guest visible behaviour for existing machine
versions).

I think the line above will do that.

> +    if (!ppc_type_check_compat(cputype, CPU_POWERPC_LOGICAL_3_00,
> +                               0, spapr->max_compat_pvr)) {
> +        caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = 0;

And this part I think is redundant, because hdecr_bits won't be large
for anything pre-POWER9.

> +    }
> +
>      if (!ppc_type_check_compat(cputype, CPU_POWERPC_LOGICAL_2_07,
>                                 0, spapr->max_compat_pvr)) {
>          caps.caps[SPAPR_CAP_HTM] = SPAPR_CAP_OFF;

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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