Re: [PATCH 0/8] cpufreq: Auto-register with energy model

[Quentin Perret]

On Tuesday 10 Aug 2021 at 13:06:47 (+0530), Viresh Kumar wrote:
> Provide a cpufreq driver flag so drivers can ask the cpufreq core to register
> with the EM core on their behalf.

Hmm, that's not quite what this does. This asks the cpufreq core to
use *PM_OPP* to register an EM, which I think is kinda wrong to do from
there IMO. The decision to use PM_OPP or another mechanism to register
an EM belongs to platform specific code (drivers), so it is odd for the
PM_OPP registration to have its own cpufreq flag but not the other ways.

As mentioned in another thread, the very reason to have PM_EM is to not
depend on PM_OPP, so I'm worried about the direction of travel with this
series TBH.

> This allows us to get rid of duplicated code
> in the drivers and fix the unregistration part as well, which none of the
> drivers have done until now.

This series adds more code than it removes, and the unregistration is
not a fix as we don't ever remove the EM tables by design, so not sure
either of these points are valid arguments.

> This would also make the registration with EM core to happen only after policy
> is fully initialized, and the EM core can do other stuff from in there, like
> marking frequencies as inefficient (WIP). Though this patchset is useful without
> that work being done and should be merged nevertheless.
> 
> This doesn't update scmi cpufreq driver for now as it is a special case and need
> to be handled differently. Though we can make it work with this if required.

Note that we'll have more 'special cases' if other architectures start
using PM_EM, which is what we have been trying to allow since the
beginning, so that's worth keeping in mind.

Thanks,
Quentin