Messages in this thread | | | Date | Fri, 6 Jul 2018 11:18:58 +0100 | From | Quentin Perret <> | Subject | Re: [RFC PATCH v4 12/12] OPTIONAL: cpufreq: dt: Register an Energy Model |
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On Friday 06 Jul 2018 at 12:10:02 (+0200), Vincent Guittot wrote: > On Thu, 28 Jun 2018 at 13:41, Quentin Perret <quentin.perret@arm.com> wrote: > > +static int of_est_power(unsigned long *mW, unsigned long *KHz, int cpu) > > +{ > > + unsigned long mV, Hz, MHz; > > + struct device *cpu_dev; > > + struct dev_pm_opp *opp; > > + struct device_node *np; > > + u32 cap; > > + u64 tmp; > > + > > + cpu_dev = get_cpu_device(cpu); > > + if (!cpu_dev) > > + return -ENODEV; > > + > > + np = of_node_get(cpu_dev->of_node); > > + if (!np) > > + return -EINVAL; > > + > > + if (of_property_read_u32(np, "dynamic-power-coefficient", &cap)) > > + return -EINVAL; > > + > > + Hz = *KHz * 1000; > > + opp = dev_pm_opp_find_freq_ceil(cpu_dev, &Hz); > > + if (IS_ERR(opp)) > > + return -EINVAL; > > + > > + mV = dev_pm_opp_get_voltage(opp) / 1000; > > + dev_pm_opp_put(opp); > > + > > + MHz = Hz / 1000000; > > + tmp = (u64)cap * mV * mV * MHz; > > + do_div(tmp, 1000000000); > > Could you explain the formula above ? and especially the 1000000000 it > seems related to the use of mV and mW instead of uV and uW ...
That's correct, this is just a matter of units. I simply tried to reproduce here what is currently done for IPA:
https://elixir.bootlin.com/linux/latest/source/drivers/thermal/cpu_cooling.c#L252
> > Can't you just optimize that into > tmp = (u64)cap * mV * mV * Hz; > do_div(tmp, 1000);
I don't think that'll work. If you use Hz instead of MHz you'll need to divide tmp by 1000000000000000 to get milli-watts, as specified by the EM framework.
FYI, I don't consider this patch to be ready to be merged. I kept it self-contained and simple for the example but I actually think that this of_est_power function should probably be factored-out somewhere else. scpi-cpufreq could use it as well. Anyway, I guess we can discuss that later once the APIs of the EM framework are agreed :-)
Thanks, Quentin
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