Messages in this thread | | | Date | Wed, 6 Mar 2019 15:19:10 -0700 | From | Lina Iyer <> | Subject | Re: [PATCH RESEND v3 2/3] drivers: qcom: rpmh-rsc: return if the controller is idle |
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On Wed, Mar 06 2019 at 15:12 -0700, Stephen Boyd wrote: >Quoting Lina Iyer (2019-03-04 09:14:50) >> On Fri, Mar 01 2019 at 10:58 -0700, Stephen Boyd wrote: >> >Quoting Lina Iyer (2019-02-27 14:29:13) >> >> Hi Stephen, >> >> >> >> On Tue, Feb 26 2019 at 17:49 -0700, Stephen Boyd wrote: >> > >> >Ok, can you explain why it's even a problem for the TCSes to be active >> >during suspend? I would hope that for suspend/resume, if this is >> >actually a problem, the RPMh driver itself can block suspend with a >> >driver suspend callback that checks for idleness. >> The RSC can transmit TCS executed from Linux and when all the CPUs have >> powered down, could execute a firmware in the RSC to deliver the sleep >> state requests. The firmware cannot run when there are active requests >> being processed. To ensure that case, we bail out of sleep or suspend, >> when the last CPU is powering down, if there are active requests. > >Ok, do we actually bail out or just pick a shallower idle state that >wouldn't trigger the firmware to run something that may conflict with >the active requests (i.e. some light CPU sleep mode)? The commit text >seems to imply we block certain idle states. > We bail out of idle and let cpuidle determine the state again. We don't go into a shallower state. >> >> >But I suspect that in >> >the system wide suspend/resume case, any callers that could make TCS >> >requests are child devices of the RPMh controller and therefore they >> >would already be suspended if they didn't have anything pending they're >> >waiting for a response on or they would be blocking suspend themselves >> >if they're waiting for the response. So why are we even checking the >> >TCSes in system suspend path at all? Assume that callers know what >> >they're doing and will block suspend if they care? >> > >> In suspend, they probably would do what you mention above. All CPUs >> might conincidentally be idle at the same idle, when a request is being >> processed. >> >> >Following that same logic, is this more of an API that is planned for >> >use by CPU idle? Where the case is much more of a runtime PM design. >> >Even then, I don't get it. A device that's runtime active and making >> >RPMh requests might need to block some forms of CPU idle states because >> >a request hasn't been processed yet that may change the decision for >> >certain deep idle states? >> > >> A process waiting on a RPMH request, may let the CPU go to sleep and >> therefore this is a possibility. >> > >Ok thanks for the info. Can these details be included in the commit text >so we don't lose sight of the bigger picture? And can this patch series >be combined with a larger cpuidle/suspend patch series so we don't have >to review this in isolation? I don't understand the need to add more >APIs that aren't used yet. > Agreed.
--Lina
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