Re: [PATCH] devfreq: Register devfreq as a cooling device

[Lukasz Luba <lukasz.luba@arm.com>]

Hi Daniel,

On 3/4/21 12:50 PM, Daniel Lezcano wrote:
> Currently the default behavior is to manually having the devfreq
> backend to register themselves as a devfreq cooling device.
> 
> There are no so many and actually it makes more sense to register the
> devfreq device when adding it.
> 
> Consequently, every devfreq becomes a cooling device like cpufreq is.
> 
> Having a devfreq being registered as a cooling device can not mitigate
> a thermal zone if it is not bound to this one. Thus, the current
> configurations are not impacted by this change.

There are also different type of devices, which register into devfreq
framework like NoC buses, UFS/eMMC, jpeg and video accelerators, ISP,
etc.
In some platforms there are plenty of those devices and they all would
occupy memory due to private freq_table in devfreq_cooling, function:
devfreq_cooling_gen_tables().

IIRC in OdroidXU4 there are ~20 devfreq devs for NoC buses.

It's true that they will not affect thermal zones, but unnecessarily,
they all will show up in the /sys/class/thermal/ as
thermal-devfreq-X.

IMO the devfreq shouldn't be tight with devfreq cooling thermal.

CpuFreq is different because it handles only CPUs. Here we have
many different devices.

Regards,
Lukasz