Re: [PATCH 4/7] cpufreq: amd_pstate: add AMD pstate EPP support for shared memory type processor

[Limonciello, Mario]

On 9/9/2022 11:45, Perry Yuan wrote:
> Add Energy Performance Preference support for AMD SOCs which only
> support the shared memory interface that implemented on Zen2 and Zen3
> processors, because this type CPU has no MSR supported, it will use
> ACPI PCC channel to enable EPP and reset desired perf to be zero.

This reads like all Zen2 and Zen3 processors don't have the MSR, but 
that's not true. How about:

"Add Energy Performance Preference support for AMD SOCs which do not 
contain a designated MSR for CPPC support. A shared memory interface
is used for CPPC on these SOCs and the ACPI PCC channel is used to
enable EPP and reset the desired performance."

> Signed-off-by: Perry Yuan <Perry.Yuan@xxxxxxx>
> ---
>   drivers/cpufreq/amd-pstate.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 451295284a26..fff298744a8e 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -133,12 +133,24 @@ static inline int pstate_enable(bool enable)
>   
>   static int cppc_enable(bool enable)
>   {
> +	struct cppc_perf_ctrls perf_ctrls;
>   	int cpu, ret = 0;
>   
>   	for_each_present_cpu(cpu) {
>   		ret = cppc_set_enable(cpu, enable);
>   		if (ret)
>   			return ret;
> +
> +	/* Enable active mode for EPP */
> +	ret = cppc_set_auto_epp(cpu, enable);
> +	if (ret)
> +		return ret;
> +
> +	/* Set zero to desired perf to enable EPP control*/
> +	perf_ctrls.desired_perf = 0;
> +	ret = cppc_set_perf(cpu, &perf_ctrls);
> +	if (ret)
> +		return ret;
>   	}
>   
>   	return ret;