Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Fri, 22 Oct 2021 15:08:06 +0200 | Subject | Re: [PATCH 2/2] PM: sleep: Fix runtime PM based cpuidle support |
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On Fri, Oct 22, 2021 at 2:57 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > On Fri, 22 Oct 2021 at 14:02, Rafael J. Wysocki <rafael@kernel.org> wrote: > > > > On Fri, Oct 22, 2021 at 12:18 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > > > > > On Thu, 21 Oct 2021 at 21:56, Ulf Hansson <ulf.hansson@linaro.org> wrote: > > > > > > > > On Thu, 21 Oct 2021 at 21:02, Rafael J. Wysocki <rafael@kernel.org> wrote: > > > > > > > > > > On Thu, Oct 21, 2021 at 8:12 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > > > > > > > > > > > On Thu, 21 Oct 2021 at 18:33, Rafael J. Wysocki <rafael@kernel.org> wrote: > > > > > > > > > > > > > > On Thu, Oct 21, 2021 at 6:17 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > > > > > > > > > [cut] > > > > > > > > > > > > So in theory you could check the pm_runtime_put_sync_suspend() return > > > > > > > value and fall back to something like WFI if that's an error code. > > > > > > > > > > > > I have already tried that, but it simply got too complicated. The main > > > > > > issue was that runtime PM could become disabled for the device in the > > > > > > middle of executing the ->enter() callback. > > > > > > > > > > So IIUC the problem is that you cannot resume after suspending in that case. > > > > > > > > > > IOW, you need to guarantee that if the suspend is successful, the > > > > > resume also will take place, but if the suspend fails, you basically > > > > > don't care. > > > > > > > > Exactly. > > > > > > > > > > > > > > > For example, if pm_runtime_get_sync() fails, I still need to make sure > > > > > > the reference counting in genpd becomes correct - and I can't do that > > > > > > using dev_pm_genpd_resume(). That's because it's not designed to be > > > > > > called in this "unknown" suspend phase, but should be called after the > > > > > > noirq phase and be properly balanced with dev_pm_genpd_suspend(). > > > > > > > > > > > > In other words, the error path didn't work out for me. > > > > > > > > > > It should be sufficient to call wake_up_all_idle_cpus() in the suspend > > > > > path before dpm_suspend_late(), because system suspend acquires a > > > > > PM-runtime reference on every device. IOW, it won't let any devices > > > > > runtime-suspend, so if your power domain devices are resumed in that > > > > > path, they will never suspend again in it and the > > > > > pm_runtime_put_sync_suspend() in __psci_enter_domain_idle_state() > > > > > becomes a reference counter management call which works regardless of > > > > > whether or not PM runtime is disabled. > > > > > > > > That sounds like a great idea, this should work too! Then the question > > > > is, how to make that call to wake_up_all_idle_cpus() to become > > > > optional - or only invoked for the cpuidle drivers that need it. > > > > It need not be optional. > > > > For suspend-to-idle it doesn't matter, because all CPUs will be woken > > up from idle shortly anyway. > > > > For other suspend variants this doesn't matter, because all secondary > > CPUs will be taken offline shortly and the primary CPU will call into > > the platform "sleep" handler. > > > > > > > > > > In any case, I will try this out, thanks for the suggestion! > > > > > > I now recall that I have already tried this, but unfortunately it doesn't work. > > > > > > The problem is that the dev->power.syscore flag is set for the device, > > > which makes device_prepare() to bail out early and skip calling > > > pm_runtime_get_noresume(). > > > > This needs to be fixed, then. > > So bumping the usage count even if the dev->power.syscore is set, > should be fine? (And of course dropping it in the complete phase).
Yes, please see https://patchwork.kernel.org/project/linux-pm/patch/5773062.lOV4Wx5bFT@kreacher/
It should have been done this way from the outset, but I messed up a merge (and said that it was "trivial" :-/).
> I can work with that, let me try!
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