[RFC PATCH 4/9] opp: core: Don't warn if required OPP device does not exist

[Ulf Hansson]

On Thu, 14 Oct 2021 at 13:43, Hector Martin <marcan at marcan.st> wrote:
>
> On 14/10/2021 18.55, Ulf Hansson wrote:
> > Yes, this sounds like you should move away from modeling the memory
> > part as a parent genpd for the CPUs' genpd.
> >
> > As Viresh pointed out, a devfreq driver seems like a better way to do
> > this. As a matter of fact, there are already devfreq drivers that do
> > this, unless I am mistaken.
> >
> > It looks like devfreq providers are listening to opp/cpufreq
> > notifiers, as to get an indication of when it could make sense to
> > change a performance state.
> >
> > In some cases the devfreq provider is also modeled as an interconnect
> > provider, allowing consumers to specify memory bandwidth constraints,
> > which may trigger a new performance state to be set for the memory
> > controller.
> >
> > In the tegra case, the memory controller is modelled as an
> > interconnect provider and the devfreq node is modelled as an
> > interconnect-consumer of the memory controller. Perhaps this can work
> > for apple SoCs too?
>
> I was poking around and noticed the OPP core can already integrate with
> interconnect requirements, so perhaps the memory controller can be an
> interconnect provider, and the CPU nodes can directly reference it as a
> consumer? This seems like a more accurate model of what the hardware
> does, and I think I saw some devices doing this already.

Yeah, that could work too. And, yes, I agree, it may be a better
description of the HW.

>
> (only problem is I have no idea of the actual bandwidth numbers involved
> here... I'll have to run some benchmarks to make sure this isn't just
> completely dummy data)
>
> >
> > That said, perhaps as an option to move forward, we can try to get the
> > cpufreq pieces solved first. Then as a step on top, add the
> > performance scaling for the memory controller?
>
> Sure; that's a pretty much independent part of this patchset, though I'm
> thinking I might as well try some things out for v2 anyway; if it looks
> like it'll take longer we can split it out and do just the cpufreq side.

In any case, I do my best to help with review.

Kind regards
Uffe