On 01-07-20, 18:05, Rafael J. Wysocki wrote:

On Wed, Jul 1, 2020 at 3:33 PM Ionela Voinescu [off-list ref] wrote:

quoted

On Wednesday 01 Jul 2020 at 16:16:17 (+0530), Viresh Kumar wrote:

quoted

I will rather suggest CPUFREQ_SKIP_SET_FREQ_SCALE as the name and
functionality. We need to give drivers a choice if they do not want
the core to do it on their behalf, because they are doing it on their
own or they don't want to do it.

Well, this would go backwards to me, as we seem to be designing an
opt-out flag for something that's not even implemented already.

I would go for an opt-in instead.  That would be much cleaner and less
prone to regressions IMO.

That's fine, I just wanted an option for drivers to opt-out of this
thing. I felt okay with the opt-out flag as this should be enabled for
most of the drivers and so enabling by default looked okay as well.

quoted

In this case we would not be able to tell if cpufreq (driver or core)
can provide the frequency scale factor, so we would not be able to tell
if the system is really frequency invariant; CPUFREQ_SKIP_SET_FREQ_SCALE

That is easy to fix. Let the drivers call
enable_cpufreq_freq_invariance() and set the flag.

quoted

would be set if either:
 - the driver calls arch_set_freq_scale() on its own
 - the driver does not want arch_set_freq_scale() to be called.

So at the core level we would not be able to distinguish between the
two, and return whether cpufreq-based invariance is supported.

I don't really see a reason why a driver would not want to set the
frequency scale factor

A simple case where the driver doesn't have any idea what the real
freq of the CPU is and it doesn't have counters to guess it as well.

There can be other reasons which we aren't able to imagine at this
point of time.

-- 
viresh

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