linux-kernel - Re: [PATCH 2/2] cpufreq: intel_pstate: enable HWP after resumed

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Date:   Thu, 08 Feb 2018 11:12:05 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Yu Chen <yu.c.chen@...el.com>
Cc:     Len Brown <lenb@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] cpufreq: intel_pstate: enable HWP after resumed

On Monday, January 29, 2018 3:27:57 AM CET Yu Chen wrote:
> When maxcpus=1 is appended the BP is responsible
> for re-enabling the HWP - because currently only
> the APs invoke intel_pstate_hwp_enable() during
> their online process - which might put the system
> into unstable state after resume.
> 
> Fix this by enabling the HWP explicitly on BP during
> resume.
> 
> Reported-by: Doug Smythies <dsmythies@...us.net>
> Suggested-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Signed-off-by: Yu Chen <yu.c.chen@...el.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 93a0e88bef76..89f637e8439c 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -779,6 +779,8 @@ static int intel_pstate_hwp_save_state(struct cpufreq_policy *policy)
>  	return 0;
>  }
>  
> +static void intel_pstate_hwp_enable(struct cpudata *cpudata);
> +
>  static int intel_pstate_resume(struct cpufreq_policy *policy)
>  {
>  	if (!hwp_active)
> @@ -786,6 +788,8 @@ static int intel_pstate_resume(struct cpufreq_policy *policy)
>  
>  	mutex_lock(&intel_pstate_limits_lock);
>  
> +	if (!policy->cpu)
> +		intel_pstate_hwp_enable(all_cpu_data[policy->cpu]);
>  	all_cpu_data[policy->cpu]->epp_policy = 0;
>  	intel_pstate_hwp_set(policy->cpu);
>  
> 

I've applied this one (with minor modifications) as a temporary measure, but
it is based on the CPU0=BP assumption which may not be the case.