linux-kernel - Re: [RESEND PATCH V2 6/9] cpufreq: amd_pstate: add AMD pstate EPP support for shared memory type processor

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Date:   Mon, 17 Oct 2022 18:54:48 +0800
From:   Huang Rui <ray.huang@....com>
To:     "Yuan, Perry" <Perry.Yuan@....com>
Cc:     "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "Sharma, Deepak" <Deepak.Sharma@....com>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        "Fontenot, Nathan" <Nathan.Fontenot@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Huang, Shimmer" <Shimmer.Huang@....com>,
        "Du, Xiaojian" <Xiaojian.Du@....com>,
        "Meng, Li (Jassmine)" <Li.Meng@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH V2 6/9] cpufreq: amd_pstate: add AMD pstate EPP
 support for shared memory type processor

On Tue, Oct 11, 2022 at 12:22:45AM +0800, Yuan, Perry wrote:
> 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@....com>
> ---
>  drivers/cpufreq/amd-pstate.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 2d28f458589c..08f9e335f97c 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -135,12 +135,25 @@ 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;
> +		if (epp) {
> +			/* Enable autonomous mode for EPP */
> +			ret = cppc_set_auto_epp(cpu, enable);
> +			if (ret)
> +				return ret;
> +
> +			/* Set desired perf as zero to allow EPP firmware control */
> +			perf_ctrls.desired_perf = 0;
> +			ret = cppc_set_perf(cpu, &perf_ctrls);
> +			if (ret)
> +				return ret;
> +		}

This patch only writes the desired_perf as 0 to enable the EPP function,
but it cannot be an independent function or patch without the dependency of
the next one (patch 7).

Thanks,
Ray