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    SubjectRe: [PATCH v2 2/3] cpufreq: qcom-nvmem: Enable virtual power domain devices
    On Thu, 19 Oct 2023 at 12:24, Ulf Hansson <ulf.hansson@linaro.org> wrote:
    >
    > On Wed, 18 Oct 2023 at 10:06, Stephan Gerhold
    > <stephan.gerhold@kernkonzept.com> wrote:
    > >
    > > The genpd core caches performance state votes from devices that are
    > > runtime suspended as of commit 3c5a272202c2 ("PM: domains: Improve
    > > runtime PM performance state handling"). They get applied once the
    > > device becomes active again.
    > >
    > > To attach the power domains needed by qcom-cpufreq-nvmem the OPP core
    > > calls genpd_dev_pm_attach_by_id(). This results in "virtual" dummy
    > > devices that use runtime PM only to control the enable and performance
    > > state for the attached power domain.
    > >
    > > However, at the moment nothing ever resumes the virtual devices created
    > > for qcom-cpufreq-nvmem. They remain permanently runtime suspended. This
    > > means that performance state votes made during cpufreq scaling get
    > > always cached and never applied to the hardware.
    > >
    > > Fix this by enabling the devices after attaching them and use
    > > dev_pm_syscore_device() to ensure the power domains also stay on when
    > > going to suspend. Since it supplies the CPU we can never turn it off
    > > from Linux. There are other mechanisms to turn it off when needed,
    > > usually in the RPM firmware (RPMPD) or the cpuidle path (CPR genpd).
    >
    > I believe we discussed using dev_pm_syscore_device() for the previous
    > version. It's not intended to be used for things like the above.
    >
    > Moreover, I was under the impression that it wasn't really needed. In
    > fact, I would think that this actually breaks things for system
    > suspend/resume, as in this case the cpr driver's genpd
    > ->power_on|off() callbacks are no longer getting called due this,
    > which means that the cpr state machine isn't going to be restored
    > properly. Or did I get this wrong?

    BTW, if you really need something like the above, the proper way to do
    it would instead be to call device_set_awake_path() for the device.

    This informs genpd that the device needs to stay powered-on during
    system suspend (assuming that GENPD_FLAG_ACTIVE_WAKEUP has been set
    for it), hence it will keep the corresponding PM domain powered-on
    too.

    [...]

    Kind regards
    Uffe

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