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

From: Stephan Gerhold <stephan@gerhold.net>
To: Niklas Cassel <nks@flawful.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>,
	Loic Poulain <loic.poulain@linaro.org>,
	agross@kernel.org, linux-arm-msm@vger.kernel.org,
	Viresh Kumar <vireshk@kernel.org>
Subject: Re: [PATCH] arch: arm64: dts: apq8016-dbc: Add missing cpu opps
Date: Thu, 28 May 2020 15:32:30 +0200	[thread overview]
Message-ID: <20200528133230.GA1469@gerhold.net> (raw)
In-Reply-To: <20200527231025.GA32707@flawful.org>

On Thu, May 28, 2020 at 01:10:25AM +0200, Niklas Cassel wrote:
> 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.
> 

I will try to come up with something like that, thank you!

> > 
> > 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 :)

I'm a bit confused at the moment, but it's mainly because we discussed
so many different options. I will need some time to properly look
at all of them and come up with a potential solution.

Thanks for taking the time to answer all my questions! :)
Stephan