On Fri, Mar 22, 2019 at 11:45 PM Srinivas Pandruvada
<srinivas.pandruvada@xxxxxxxxxxxxxxx> wrote:
>
> ACPI specifications stat that if the "Guaranteed Performance Register" is
> not implemented, OSPM assumes guaranteed performance is always equal to
> nominal performance. So for invalid and unimplemented guaranteed
> performance register, use nominal performance as guaranteed performance.
>
> This change will fallback to nominal_perf when guranteed_perf is invalid.
> If nominal_perf is also invalid, then fallback to existing implementation,
> which is to read from HWP Capabilities MSR.
>
> Fixes: 86d333a8cc7f ("cpufreq: intel_pstate: Add base_frequency attribute")
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> Cc: 4.20+ <stable@xxxxxxxxxxxxxxx> # 4.20+
> ---
> drivers/cpufreq/intel_pstate.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 7b4b0a7ac68b..e16dea241c55 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -385,6 +385,9 @@ static int intel_pstate_get_cppc_guranteed(int cpu)
> if (ret)
> return ret;
>
> + if (!cppc_perf.guaranteed_perf)
> + return cppc_perf.nominal_perf;
> +
> return cppc_perf.guaranteed_perf;
> }
I would do this the other way around, that is
if (cppc_perf.guaranteed_perf)
return cppc_perf.guaranteed_perf;
return cppc_perf.nominal_perf;
That is slightly easier to follow IMO.
