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Date:   Thu, 10 Nov 2022 10:19:44 -0600
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Subject: Re: [PATCH v3 6/8] cpufreq: amd-pstate: implement suspend and resume
 callbacks
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To:     Perry Yuan <Perry.Yuan@amd.com>, rafael.j.wysocki@intel.com,
        ray.huang@amd.com, viresh.kumar@linaro.org
Cc:     Deepak.Sharma@amd.com, Mario.Limonciello@amd.com,
        Alexander.Deucher@amd.com, Shimmer.Huang@amd.com,
        Xiaojian.Du@amd.com, Li.Meng@amd.com, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20221107175705.2207842-1-Perry.Yuan@amd.com>
 <20221107175705.2207842-7-Perry.Yuan@amd.com>
From:   Nathan Fontenot <nathan.fontenot@amd.com>
In-Reply-To: <20221107175705.2207842-7-Perry.Yuan@amd.com>
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On 11/7/22 11:57, Perry Yuan wrote:
> add suspend and resume support for the AMD processors by amd_pstate_epp
> driver instance.
> 
> When the CPPC is suspended, EPP driver will set EPP profile to 'power'
> profile and set max/min perf to lowest perf value.
> When resume happens, it will restore the MSR registers with
> previous cached value.
> 
> Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
> ---
>  drivers/cpufreq/amd-pstate.c | 40 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 6ce9fca0a128..841b1e2383b8 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1282,6 +1282,44 @@ static int amd_pstate_epp_cpu_offline(struct cpufreq_policy *policy)
>  	return amd_pstate_cpu_offline(policy);
>  }
>  
> +static int amd_pstate_epp_suspend(struct cpufreq_policy *policy)
> +{
> +	struct amd_cpudata *cpudata = all_cpu_data[policy->cpu];
> +	int ret;
> +
> +	/* avoid suspending when EPP is not enabled */
> +	if (!cppc_active)
> +		return 0;
> +
> +	/* set this flag to avoid setting core offline*/
> +	cpudata->suspended = true;

Shouldn't we set this only after the amd_pstate_enable(false) call succeeds?

> +
> +	/* disable CPPC in lowlevel firmware */
> +	ret = amd_pstate_enable(false);
> +	if (ret)
> +		pr_err("failed to suspend, return %d\n", ret);
> +
> +	return 0;

You could drop the checking of ret here and just return ret. The caller
cpufreq.c:cpufreq_suspend() already does a check of the return code and
prints an error message.

> +}
> +
> +static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
> +{
> +	struct amd_cpudata *cpudata = all_cpu_data[policy->cpu];
> +
> +	if (cpudata->suspended) {
> +		mutex_lock(&amd_pstate_limits_lock);
> +
> +		/* enable amd pstate from suspend state*/
> +		amd_pstate_epp_reenable(cpudata);

This call can fail, we should check the return code.

-Nathan

> +
> +		mutex_unlock(&amd_pstate_limits_lock);
> +
> +		cpudata->suspended = false;
> +	}
> +
> +	return 0;
> +}
> +
>  static void amd_pstate_verify_cpu_policy(struct amd_cpudata *cpudata,
>  					   struct cpufreq_policy_data *policy)
>  {
> @@ -1318,6 +1356,8 @@ static struct cpufreq_driver amd_pstate_epp_driver = {
>  	.update_limits	= amd_pstate_epp_update_limits,
>  	.offline	= amd_pstate_epp_cpu_offline,
>  	.online		= amd_pstate_epp_cpu_online,
> +	.suspend	= amd_pstate_epp_suspend,
> +	.resume		= amd_pstate_epp_resume,
>  	.name		= "amd_pstate_epp",
>  	.attr		= amd_pstate_epp_attr,
>  };