linux-kernel - Re: [PATCH] cpufreq: scmi: Fix frequency invariance in slow path

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Date:   Wed, 09 Jan 2019 12:03:49 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Quentin Perret <quentin.perret@....com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>, sudeep.holla@....com,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        qais.yousef@....com
Subject: Re: [PATCH] cpufreq: scmi: Fix frequency invariance in slow path

On Wednesday, January 9, 2019 11:59:05 AM CET Quentin Perret wrote:
> On Wednesday 09 Jan 2019 at 11:56:06 (+0100), Rafael J. Wysocki wrote:
> > On Wednesday, January 9, 2019 11:45:11 AM CET Viresh Kumar wrote:
> > > On 09-01-19, 10:42, Quentin Perret wrote:
> > > > The scmi-cpufreq driver calls the arch_set_freq_scale() callback on
> > > > frequency changes to provide scale-invariant load-tracking signals to
> > > > the scheduler. However, in the slow path, it does so while specifying
> > > > the current and max frequencies in different units, hence resulting in a
> > > > broken freq_scale factor.
> > > > 
> > > > Fix this by passing all frequencies in KHz, as stored in the CPUFreq
> > > > frequency table.
> > > > 
> > > > Fixes: 99d6bdf33877 ("cpufreq: add support for CPU DVFS based on SCMI
> > > > message protocol")
> > > > Signed-off-by: Quentin Perret <quentin.perret@....com>
> > > > ---
> > > >  drivers/cpufreq/scmi-cpufreq.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
> > > > index 50b1551ba894..3f0693439486 100644
> > > > --- a/drivers/cpufreq/scmi-cpufreq.c
> > > > +++ b/drivers/cpufreq/scmi-cpufreq.c
> > > > @@ -52,9 +52,9 @@ scmi_cpufreq_set_target(struct cpufreq_policy *policy, unsigned int index)
> > > >  	int ret;
> > > >  	struct scmi_data *priv = policy->driver_data;
> > > >  	struct scmi_perf_ops *perf_ops = handle->perf_ops;
> > > > -	u64 freq = policy->freq_table[index].frequency * 1000;
> > > > +	u64 freq = policy->freq_table[index].frequency;
> > > >  
> > > > -	ret = perf_ops->freq_set(handle, priv->domain_id, freq, false);
> > > > +	ret = perf_ops->freq_set(handle, priv->domain_id, freq * 1000, false);
> > > >  	if (!ret)
> > > >  		arch_set_freq_scale(policy->related_cpus, freq,
> > > >  				    policy->cpuinfo.max_freq);
> > > 
> > > Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> > 
> > This would be stable-candidate I guess?
> 
> I think so yes. I was hoping the 'Fixes:' tag would be enough ?

It doesn't cause -stable to pick up commits automatically if that's
what you're asking about.

> Or do I still need to CC stable too ?

No, you don't need to (and should not) CC -stable yourself.

You can, however, add a Cc: <stable..> tag to the patch which helps
maintainers a bit.