Re: [Question] About handling PMU context loss in the deepest idle state where the core is powered down

On Thu, Jan 09, 2020 at 03:03:19PM +0000, Will Deacon wrote:

[+Lorenzo]

On Thu, Jan 09, 2020 at 10:43:40AM +0800, Xiongfeng Wang wrote:

quoted

Sorry to bother you. It's just that we have come across some problems
about PMU recently.

No bother, and thanks for including the mailing list.

quoted

We are working on deep power state on CPU cores. In the deepest idle
state, the core will be powered down. In our implementation, the PMU
and the core are in the same power domain, so the PMU will also be
powered down. But I didn't find where we saved the PMU context in
kernel before entering the deepest idle state.

Before we enter the system sleep state, we update the kernel PMU
counter and stop the PMU in 'cpu_pm_pmu_notify()'. But we didn't do
that before we enter idle state.

ACPI or DT firmware ? I suspect that's ACPI, with LPI idle state
flags set to 0x0 (3.1.3 - save and restore flags):

http://infocenter.arm.com/help/topic/com.arm.doc.den0048a/DEN0048A_ARM_FFH_Specification.pdf

If that's the case a firmware update is needed (ie currently the kernel
expects the PMU state to be retained).

arch/arm64/kernel/cpuidle.c

ARM64_LPI_IS_RETENTION_STATE()

In DT in the PSCI CPUidle driver we run the notifiers irrespective
of the idle state depth so I don't think this behaviour can happen
in a DT bootstrapped system.

I am just guessing - please let me know if my assumption is correct.

quoted

I only find some system registers saving in 'psci_cpu_suspend_enter()->cpu_susend()->cpu_do_suspend()'

I'm not sure what you mean by "system sleep state"

I think they mean suspend-to-RAM - in suspend-to-RAM the notifiers
are run through syscore operations which are decoupled from CPUidle.

Regardless, CPUidle should call the notifiers if instructed by firmware
correctly.

Thanks,
Lorenzo

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