cpufreq: qcom-nvmem: Preserve PM domain votes in system suspend
>From the Linux point of view, the power domains used by the CPU must stay always-on. This is because we still need the CPU to keep running until the last instruction, which will typically be a firmware call that shuts down the CPU cleanly. At the moment the power domain votes (enable + performance state) are dropped during system suspend, which means the CPU could potentially malfunction while entering suspend. We need to distinguish between two different setups used with qcom-cpufreq-nvmem: 1. CPR power domain: The backing regulator used by CPR should stay always-on in Linux; it is typically disabled automatically by hardware when the CPU enters a deep idle state. However, we should pause the CPR state machine during system suspend. 2. RPMPD: The power domains used by the CPU should stay always-on in Linux (also across system suspend). The CPU typically only uses the *_AO ("active-only") variants of the power domains in RPMPD. For those, the RPM firmware will automatically drop the votes internally when the CPU enters a deep idle state. Make this work correctly by calling device_set_awake_path() on the virtual genpd devices, so that the votes are maintained across system suspend. The power domain drivers need to set GENPD_FLAG_ACTIVE_WAKEUP to opt into staying on during system suspend. For now we only set this for the RPMPD case. For CPR, not setting it will ensure the state machine is still paused during system suspend, while the backing regulator will stay on with "regulator-always-on". Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
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