On Thu, 14 Oct 2021 at 13:43, Hector Martin <marcan@xxxxxxxxx> 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
