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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 16 Oct 2020 17:41:33 +0200
Message-ID: <CAJZ5v0iTn34nE6u2SK2Niz_NmQi8O7QUjPAkCZY2Mo42WzDAiw@mail.gmail.com>
Subject: Re: [PATCH v3] PM: domains: Add support for PM domain on/off
 notifiers for genpd
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Kevin Hilman <khilman@kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Peng Fan <peng.fan@nxp.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Lina Iyer <ilina@codeaurora.org>,
        Lukasz Luba <lukasz.luba@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Oct 13, 2020 at 2:23 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> A device may have specific HW constraints that must be obeyed to, before
> its corresponding PM domain (genpd) can be powered off - and vice verse at
> power on. These constraints can't be managed through the regular runtime PM
> based deployment for a device, because the access pattern for it, isn't
> always request based. In other words, using the runtime PM callbacks to
> deal with the constraints doesn't work for these cases.
>
> For these reasons, let's instead add a PM domain power on/off notification
> mechanism to genpd. To add/remove a notifier for a device, the device must
> already have been attached to the genpd, which also means that it needs to
> be a part of the PM domain topology.
>
> To add/remove a notifier, let's introduce two genpd specific functions:
>  - dev_pm_genpd_add|remove_notifier()
>
> Note that, to further clarify when genpd power on/off notifiers may be
> used, one can compare with the existing CPU_CLUSTER_PM_ENTER|EXIT
> notifiers. In the long run, the genpd power on/off notifiers should be able
> to replace them, but that requires additional genpd based platform support
> for the current users.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>
> Changes in v3:
>         - Adopted suggestions from Peng Fan to allow more fine grained levels of
>         notifications, which is needed on some NXP platforms.
>         - Move the code that fires the notifications into _genpd_power_on|off(),
>         as it simply fits better in there.
>
> Note that, I understand that some of us may be occupied with dealing with the
> merge window, but I still wanted to get this submitted to allow those that have
> some time to review and test.

Appreciated. :-)

Anyway, applied as 5.10-rc material, thanks!