Re: [PATCH] arch: arm64: dts: apq8016-dbc: Add missing cpu opps

[Niklas Cassel <nks@flawful.org>]

On Wed, May 27, 2020 at 10:56:07PM +0200, Stephan Gerhold wrote:
> > If the CPR driver is not changed, which I doubt, you will simply change
> > the device tree to remove the cpu-supply regulator and move it into the
> > new CPR DT node.
> > 
> > Old device trees will still use your DVFS solution, new device
> > trees will use the CPR DT node and will use the AVS solution.
> > 
> 
> I think my concern is essentially that I would duplicate the MEMACC code
> into a new driver utilizing .set_opp() - and to keep backwards
> compatibility we would need to keep that duplication forever.

The cleanest solution is probably to create a new memacc platform device
driver, and make the new code use that, and refactor CPR to use the same.

> 
> The MEMACC scaling isn't all that complicated, but overall I would
> prefer to avoid introducing duplication in the first place.
> 
> Also: If full CPR ever happens we would be basically back
> to one part of the current discussion: specifying two "required-opps"
> MX and CPR (= APC + MEMACC) would result in the wrong order
> when scaling up/down.
> 
> But maybe I just worry too much?

I guess that whoever implements CPR on msm8916 will either call
dev_pm_genpd_set_performance_state() on MX directly from cpr_scale_voltage()
or perhaps change OPP core so that it runs the required-opps in reverse
order when scaling down, like you previously suggested.

Please don't take my suggestions as the only way forward though.
Hopefully I provided more clarity than confusion.
Will step back so that someone else has a chance to chime in :)


Kind regards,
Niklas