Re: [Qemu-ppc] [PATCH 2/2] ppc: tcg: implement helper_nap

[Tom Musta]

On 1/14/2014 8:22 PM, Liu Ping Fan wrote:
> When nap, clear no persistent register as ISA spec says.
> 
> Signed-off-by: Liu Ping Fan <address@hidden>
> ---
>  target-ppc/excp_helper.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/target-ppc/excp_helper.c b/target-ppc/excp_helper.c
> index a9712bc..5dbb166 100644
> --- a/target-ppc/excp_helper.c
> +++ b/target-ppc/excp_helper.c
> @@ -892,6 +892,20 @@ void helper_hrfid(CPUPPCState *env)
>  
>  void helper_nap(CPUPPCState *env)
>  {
> +    int i;
> +    for (i = 0; i < 32; i++) {
> +        env->gpr[i] = 0;
> +    }
> +    env->lr = 0;
> +    env->ctr = 0;
> +    for (i = 0; i < 8; i++) {
> +        env->crf[i] = 0;
> +    }
> +    env->msr = 0;
> +    for (i = 0; i < 32; i++) {
> +        env->fpr[i] = 0;
> +    }
> +
>  }
>  #endif
>  
> 

The Power Saving Mode instructions (doze, nap, sleep, rvwinkle) all put the
hardware thread into a suspended state, including the halting of subsequent
instruction fetches.  I don't see how your patch achieves this; I suspect
that QEMU will attempt to fetch whatever instruction immediately follows
nap in the new context (MSR=0).  Can you elaborate?

Also, if you are going to add nap, why not also add doze, sleep and rvwinkle?