Re: [PATCH] KVM: PPC: e500: Emulate power management control SPR

[Scott Wood <scottwood@freescale.com>]

On Mon, 2014-06-30 at 15:55 +0300, Mihai Caraman wrote:
> For FSL e6500 core the kernel uses power management SPR register (PWRMGTCR0)
> to enable idle power down for cores and devices by setting up the idle count
> period at boot time. With the host already controlling the power management
> configuration the guest could simply benefit from it, so emulate guest request
> as nop.
> 
> Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
> ---
>  arch/powerpc/kvm/e500_emulate.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/powerpc/kvm/e500_emulate.c b/arch/powerpc/kvm/e500_emulate.c
> index 002d517..98a22e5 100644
> --- a/arch/powerpc/kvm/e500_emulate.c
> +++ b/arch/powerpc/kvm/e500_emulate.c
> @@ -250,6 +250,10 @@ int kvmppc_core_emulate_mtspr_e500(struct kvm_vcpu *vcpu, int sprn, ulong spr_va
>  				spr_val);
>  		break;
>  
> +	case SPRN_PWRMGTCR0:
> +		/* Guest relies on host power management configurations */
> +		break;
> +
>  	/* extra exceptions */
>  	case SPRN_IVOR32:
>  		vcpu->arch.ivor[BOOKE_IRQPRIO_SPE_UNAVAIL] = spr_val;
> @@ -355,6 +359,10 @@ int kvmppc_core_emulate_mfspr_e500(struct kvm_vcpu *vcpu, int sprn, ulong *spr_v
>  		*spr_val = 0;
>  		break;
>  
> +	case SPRN_PWRMGTCR0:
> +		*spr_val = 0;
> +		break;
> +
>  	case SPRN_MMUCFG:
>  		*spr_val = vcpu->arch.mmucfg;
>  		break;

When reading, is it better to return zero, or the current host value, or
the value last written by the guest (even though it wasn't written to
hardware)?

-Scott