On Thursday 15 Oct 2020 at 15:40:16 (+0200), Rafael J. Wysocki wrote: > On Thu, Oct 15, 2020 at 12:22 PM Daniel Lezcano > <daniel.lezcano@xxxxxxxxxx> wrote: > > > > On 15/10/2020 11:00, Lukasz Luba wrote: > > > > [ ... ] > > > > >> There is the SCMI and the DT. Because there are two sources where it is > > >> impossible to know if they are using the same units, we are stuck to > > >> ensure a consistency for the kernel. > > >> > > >> The platform should use: > > >> - the SCMI only (scaled or real) > > >> - the DT only (real) > > >> [ - the firmware file only (scaled or real) ] > > >> > > > > > > Do you mean by SCMI - registration using em_dev_register_perf_domain() ? > > > > It was high level description, but yes, I guess it is the case. > > > > >> As it is not possible to know if they are scaled or real, there is no > > >> choice except making them mutually exclusive. > > > > > > So you propose a bit more restriction in registration EM, to not get > > > lost in the future. I also have these doubts. Let's consider it and > > > maybe agree. > > > > > > I've recommended Qcom to use em_dev_register_perf_domain() when they > > > have this obfuscated power values. Then any developer in the future > > > who wants to add EM for a new device on that platform, should use the > > > em_dev_register_perf_domain(). > > > > > > In this case the flag in EM that you have proposed makes sense. > > > We probably need an argument 'bool abstract_scale' in the > > > em_dev_register_perf_domain(..., bool abstract_scale) > > > as a source of information. > > > > I was suggesting to add a flag to the em_perf_domain structure giving > > the source of the power numbers. > > > > So if the IPA is having the 'sustainable-power' set in DT but the > > em_perf_domain is flagged with power number coming from SCMI, then they > > will be incompatible, the thermal zone will fail to register. > > > > > > > We would allow to co-exist em_dev_register_perf_domain(..., false) > > > with dev_pm_opp_of_register_em() EM devices. > > > > > > Is it make sense? > > > > Well, it does not change my opinion. We should assume the energy model > > is always milliwatts. If the SoC vendors find a way to get around with > > bogoWatts, then good to them and up to them to deal with in the future. > > That sounds fair enough, but it also means that any kernel patches > using power units different from milliwatts for the EM should be > rejected in the future, doesn't it? > > And the existing code using different power units for the EM (if any) > should be updated/fixed accordingly, shouldn't it? > > Otherwise I don't see now this can be regarded as a hard rule. Sorry, jumping late in the discussion :) To add a bit of background to this, it's been the plan from the very beginning to make PM_EM use an abstract scale. The only reason it was not merged like that is because the first version only worked for CPUs, and IPA was using a totally different source for other devices. So we had no choice but to specify PM_EM in mW to keep things compatible and allow to transition IPA. But that is no longer true, so I'm in favor of evolving PM_EM where it was supposed to be to begin with. IMO, the only thing the kernel cares about is consistency across power numbers, but not about the exact unit. And I agree with Rafael, we have code paths in the kernel that feed data in PM_EM but _cannot_ guarantee mW, SCMI being a prime example, so I don't think it is reasonable to mandate that. Having that properly documented + an 'abstract_scale' parameter in dev_pm_opp_of_register_em() (or even a unit, which could be bogo-watts) should work IMO. What is the concern with this approach? Thanks, Quentin
