linux-kernel - Re: [PATCH] cpufreq: fix cpufreq_get() can't get correct CPU frequency

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Date:   Fri, 11 Mar 2022 09:33:12 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     z00314508 <zhengzucheng@...wei.com>
Cc:     rafael@...nel.org, viresh.kumar@...aro.org, tglx@...utronix.de,
        len.brown@...el.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] cpufreq: fix cpufreq_get() can't get correct CPU
 frequency

On Fri, Mar 11, 2022 at 04:11:11PM +0800, z00314508 wrote:
> From: Zucheng Zheng <zhengzucheng@...wei.com>
> 
> On some specific platforms, the cpufreq driver does not define
> cpufreq_driver.get() routine (eg:x86 intel_pstate driver), as a
> result, the cpufreq_get() can't get the correct CPU frequency.
> 
> Modern x86 processors include the hardware needed to accurately
> calculate frequency over an interval -- APERF, MPERF and the TSC.
> Here we use arch_freq_get_on_cpu() in preference to any driver
> driver-specific cpufreq_driver.get() routine to get CPU frequency.
> 
> Fixes: f8475cef9008 ("x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF")
> Signed-off-by: Zucheng Zheng <zhengzucheng@...wei.com>
> ---
>  drivers/cpufreq/cpufreq.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 80f535cc8a75..d777257b4454 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1806,10 +1806,14 @@ unsigned int cpufreq_get(unsigned int cpu)
>  {
>  	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
>  	unsigned int ret_freq = 0;
> +	unsigned int freq;
>  
>  	if (policy) {
>  		down_read(&policy->rwsem);
> -		if (cpufreq_driver->get)
> +		freq = arch_freq_get_on_cpu(policy->cpu);
> +		if (freq)
> +			ret_freq = freq;
> +		else if (cpufreq_driver->get)
>  			ret_freq = __cpufreq_get(policy);
>  		up_read(&policy->rwsem);
>  
> -- 
> 2.18.0.huawei.25
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>