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Date:   Tue, 19 Jul 2022 08:48:34 +0800
From:   Huang Rui <ray.huang@amd.com>
To:     "Yuan, Perry" <Perry.Yuan@amd.com>
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        "viresh.kumar@linaro.org" <viresh.kumar@linaro.org>,
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        "Limonciello, Mario" <Mario.Limonciello@amd.com>,
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        "Su, Jinzhou (Joe)" <Jinzhou.Su@amd.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 04/13] cpufreq: amd-pstate: prefetch cppc_req_cached
 value in amd_pstate_cpu_init()
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References: <cover.1657876961.git.Perry.Yuan@amd.com>
 <686bc72b4dc3a663c00126c852e3b4774a280700.1657876961.git.Perry.Yuan@amd.com>
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On Fri, Jul 15, 2022 at 06:04:23PM +0800, Yuan, Perry wrote:
> This cppc_req_cached valued should be prefetched during
> amd_pstate_cpu_init call period, then the amd_pstate_update() will get
> correct cached value before updating the perf to change the cpu perf
> level.The cached values are read through MSR interface, so here use
> shared_mem flag to check the registers are accessible
> 
> Also the core performance boost state will be initialized through
> hardware configuration register
> 
> * shared_mem flag is used for the shared memory type CPPC implementation
>   which dose not support MSR interface operation

Please check the comment of patch 2.

> 
> Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
> ---
>  drivers/cpufreq/amd-pstate.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 43e6df9f67f6..d8c4153dbe4f 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -92,6 +92,8 @@ struct amd_aperf_mperf {
>   * @prev: Last Aperf/Mperf/tsc count value read from register
>   * @freq: current cpu frequency value
>   * @boost_supported: check whether the Processor or SBIOS supports boost mode
> + * @precision_boost_off: the core performance boost disabled state
> + * @cppc_hw_conf_cached: the cached hardware configuration register
>   *
>   * The amd_cpudata is key private data for each CPU thread in AMD P-State, and
>   * represents all the attributes and goals that AMD P-State requests at runtime.
> @@ -117,6 +119,7 @@ struct amd_cpudata {
>  
>  	u64 freq;
>  	bool	boost_supported;
> +	bool	precision_boost_off;
>  	u64 	cppc_hw_conf_cached;
>  };
>  
> @@ -547,12 +550,17 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>  	cpudata->lowest_nonlinear_freq = lowest_nonlinear_freq;
>  
>  	policy->driver_data = cpudata;
> +	if (!shared_mem) {
> +		ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, &value);
> +		if (ret)
> +			return ret;
> +		cpudata->precision_boost_off = value & AMD_CPPC_PRECISION_BOOST_ENABLED;
>  
> -	ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, &value);
> -	if (ret)
> -		return ret;
> -	WRITE_ONCE(cpudata->cppc_hw_conf_cached, value);
> -
> +		ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, &value);
> +		if (ret)
> +			return ret;
> +		WRITE_ONCE(cpudata->cppc_req_cached, value);
> +	}
>  	amd_pstate_boost_init(cpudata);
>  
>  	return 0;
> -- 
> 2.32.0
>