linux-kernel - Re: [RFC][PATCH] cpufreq: intel_pstate: Delete intel_pstate sysfs if failed to register the driver

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Date:   Mon, 12 Oct 2020 06:22:40 -0700
From:   srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Chen Yu <yu.c.chen@...el.com>, Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] cpufreq: intel_pstate: Delete intel_pstate sysfs
 if failed to register the driver

On Fri, 2020-10-09 at 11:30 +0800, Chen Yu wrote:
> There is a corner case that if the intel_pstate driver failed to be
> registered(might be due to invalid MSR access) 
Do you have logs why it is not loaded? On supported platforms MSRs
should be invalid.
It may be a case when we are trying to bring up pre-production systems
where some instability in MSRs on certain CPUs. 

But the patch is correct. We can't have invalid folder when
intel_pstate is not used. 

> and with the acpi_cpufreq
> loaded, the intel_pstate sysfs might still be created, which makes
> the
> user confusing(turbostat for example):
> 
> grep . /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
> acpi-cpufreq
> 
> grep . /sys/devices/system/cpu/intel_pstate/*
> /sys/devices/system/cpu/intel_pstate/max_perf_pct:0
> /sys/devices/system/cpu/intel_pstate/min_perf_pct:0
> grep: /sys/devices/system/cpu/intel_pstate/no_turbo: Resource
> temporarily unavailable
> grep: /sys/devices/system/cpu/intel_pstate/num_pstates: Resource
> temporarily unavailable
> /sys/devices/system/cpu/intel_pstate/status:off
> grep: /sys/devices/system/cpu/intel_pstate/turbo_pct: Resource
> temporarily unavailable
> 
> The existing of intel_pstate sysfs does not mean that the
> intel_pstate driver
> has been successfully loaded(for example, echo off to status), but
> the
> intel_pstate sysfs should not co-exist when acpi-cpufreq is also
> present.
> Fix this issue by deleting the intel_pstate sysfs if the driver
> failed
> to be loaded during bootup.
> 
> Reported-by: Wendy Wang <wendy.wang@...el.com>
> Suggested-by: Zhang Rui <rui.zhang@...el.com>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com


> --->
>  drivers/cpufreq/intel_pstate.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c
> b/drivers/cpufreq/intel_pstate.c
> index 9a515c460a00..8c5f9680de83 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1420,6 +1420,26 @@ static void __init
> intel_pstate_sysfs_expose_params(void)
>  	}
>  }
>  
> +static void __init intel_pstate_sysfs_clean(void)
> +{
> +	if (!intel_pstate_kobject)
> +		return;
> +
> +	sysfs_remove_group(intel_pstate_kobject,
> &intel_pstate_attr_group);
> +
> +	if (per_cpu_limits)
> +		goto release_kobj;
> +
> +	sysfs_remove_file(intel_pstate_kobject, &max_perf_pct.attr);
> +	sysfs_remove_file(intel_pstate_kobject, &min_perf_pct.attr);
> +
> +	if (x86_match_cpu(intel_pstate_cpu_ee_disable_ids))
> +		sysfs_remove_file(intel_pstate_kobject,
> &energy_efficiency.attr);
> +
> +release_kobj:
> +	kobject_put(intel_pstate_kobject);
> +}
> +
>  static void intel_pstate_sysfs_expose_hwp_dynamic_boost(void)
>  {
>  	int rc;
> @@ -3063,8 +3083,10 @@ static int __init intel_pstate_init(void)
>  	mutex_lock(&intel_pstate_driver_lock);
>  	rc = intel_pstate_register_driver(default_driver);
>  	mutex_unlock(&intel_pstate_driver_lock);
> -	if (rc)
> +	if (rc) {
> +		intel_pstate_sysfs_clean();
>  		return rc;
> +	}
>  
>  	if (hwp_active) {
>  		const struct x86_cpu_id *id;