On Thu, Feb 06, 2020 at 01:11:33PM -0800, Bjorn Andersson wrote: > On Wed 05 Feb 06:06 PST 2020, Sudeep Holla wrote: > > > On Wed, Feb 05, 2020 at 05:53:00PM +0530, Maulik Shah wrote: > > > > > > On 2/4/2020 8:51 PM, Sudeep Holla wrote: > > > > On Tue, Feb 04, 2020 at 10:22:42AM +0530, Maulik Shah wrote: > > > > > On 2/3/2020 10:38 PM, Sudeep Holla wrote: > > > > > > On Mon, Feb 03, 2020 at 07:05:38PM +0530, Maulik Shah wrote: > > > > > > > From: Ulf Hansson <ulf.hansson@xxxxxxxxxx> > > > > > > > > > > > > > > If the hierarchical CPU topology is used, but the OS initiated mode isn't > > > > > > > supported, we need to rely solely on the regular cpuidle framework to > > > > > > > manage the idle state selection, rather than using genpd and its > > > > > > > governor. > > > > > > > > > > > > > > For this reason, introduce a new PSCI DT helper function, > > > > > > > psci_dt_pm_domains_parse_states(), which parses and converts the > > > > > > > hierarchically described domain idle states from DT, into regular flattened > > > > > > > cpuidle states. The converted states are added to the existing cpuidle > > > > > > > driver's array of idle states, which make them available for cpuidle. > > > > > > > > > > > > > And what's the main motivation for this if OSI is not supported in the > > > > > > firmware ? > > > > > Hi Sudeep, > > > > > > > > > > Main motivation is to do last-man activities before the CPU cluster can > > > > > enter a deep idle state. > > > > > > > > > Details on those last-man activities will help the discussion. Basically > > > > I am wondering what they are and why they need to done in OSPM ? > > > > > > Hi Sudeep, > > > > > > there are cases like, > > > > > > Last cpu going to deepest idle mode need to lower various resoruce > > > requirements (for eg DDR freq). > > > > > > > In PC mode, only PSCI implementation knows the last man and there shouldn't > > be any notion of it in OS. If you need it, you may need OSI. You are still > > mixing up the things. NACK for any such approach, sorry. > > > > Forgive me if I'm misunderstanding PSCI's role here, but doesn't it deal > with the power management of the "processor subsystem" in the SoC? > Yes. > In the Qualcomm platforms most resources (voltage rails, clocks, etc) > are controlled through a power controller that provides controls for a > state when the CPU subsystem is running and when it's asleep. This > allows non-CPU-related device to control if resources that are shared > with the CPU subsystem should be kept on when the last CPU/cluster goes > down. > I understand that. > An example of this would be the display controller voting to keep a > voltage rail on after the CPU subsystem collapses, because the display > is still on. > OK > But as long as the CPU subsystem is running it will keep these resources > available and there's no need to change these votes (e.g. if the display > is turned on and off while the CPU is active the sleep-requests cancels > out), so they are simply cached/batched up in the RPMh driver and what > Maulik's series is attempting to do is to flush the cached values when > Linux believes that the firmware might decide to enter a lower power > state. > I understand all these. What I am arguing is that in PC mode, PSCI firmware is the one who needs to vote and not OSPM because it is responsible for pulling the plugs off the CPU/Cluster. So lets us not bring that to OSPM. OSI was invented to do all such crazy things in OSPM, please feel free to play with that ;-) -- Regards, Sudeep
