On Fri, Oct 12, 2018 at 11:19:10AM -0600, Lina Iyer wrote: > On Fri, Oct 12 2018 at 11:01 -0600, Sudeep Holla wrote: > > On Fri, Oct 12, 2018 at 10:04:27AM -0600, Lina Iyer wrote: > > > On Fri, Oct 12 2018 at 09:04 -0600, Sudeep Holla wrote: > > > > [...] > > > > Yes all these are fine but with multiple power-domains/cluster, it's > > hard to determine the first CPU. You may be able to identify it within > > the power domain but not system wide. So this doesn't scale with large > > systems(e.g. 4 - 8 clusters with 16 CPUs). > > > We would probably not worry too much about power savings in a msec > scale, if we have that big a system. The driver is a platform specific > driver, primarily intended for a mobile class CPU and usage. In fact, we > haven't done this for QC's server class CPUs. > OK, along as there's no attempt to make it generic and keep it platform specific, I am not that bothered. > > > > I think we are mixing the system sleep states with CPU idle here. > > > > If it's system sleeps states, the we need to deal it in some system ops > > > > when it's the last CPU in the system and not the cluster/power domain. > > > > > > > I think the confusion for you is system sleep vs suspend. System sleep > > > here (probably more of a QC terminology), refers to powering down the > > > entire SoC for very small durations, while not actually suspended. The > > > drivers are unaware that this is happening. No hotplug happens and the > > > interrupts are not migrated during system sleep. When all the CPUs go > > > into cpuidle, the system sleep state is activated and the resource > > > requirements are lowered. The resources are brought back to their > > > previous active values before we exit cpuidle on any CPU. The drivers > > > have no idea that this happened. We have been doing this on QCOM SoCs > > > for a decade, so this is not something new for this SoC. Every QCOM SoC > > > has been doing this, albeit differently because of their architecture. > > > The newer ones do most of these transitions in hardware as opposed to an > > > remote CPU. But this is the first time, we are upstreaming this :) > > > > > > > Indeed, I know mobile platforms do such optimisations and I agree it may > > save power. As I mentioned above it doesn't scale well with large systems > > and also even with single power domains having multiple idle states where > > only one state can do this system level idle but not all. As I mentioned > > in the other email to Ulf, it's had to generalise this even with DT. > > So it's better to have this dealt transparently in the firmware. > > > Good, then we are on agreement here. No worries. > But this is how this platform is. It cannot be done in firmware and what > we doing here is a Linux platform driver that cleans up nicely without > having to piggy back on an external dependency. > Yes Qcom always says it can't be done in firmware. Even PSCI was adopted after couple of years of pushback. -- Regards, Sudeep
