linux-kernel - Re: [PATCH v2 3/3] PM / Domains: Add support for PM domain on/off notifiers for genpd

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Date:   Fri, 25 Sep 2020 13:48:12 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Peng Fan <peng.fan@....com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Lukasz Luba <lukasz.luba@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] PM / Domains: Add support for PM domain on/off
 notifiers for genpd

On Fri, 25 Sep 2020 at 08:08, Peng Fan <peng.fan@....com> wrote:
>
> Hi Ulf,
>
> > Subject: [PATCH v2 3/3] PM / Domains: Add support for PM domain on/off
> > notifiers for genpd
> >
> > 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.
>
> Could the notification be added before/after power on, and before/after power
> off? not just after power on and before power off?
>
> Our SoC has a requirement that before power on/off the specific module,
> the corresponding clk needs to be on to make sure the hardware async
> bridge could finish handshake.

Thanks for your comments!

May I ask, to be sure - does the clock correspond to the genpd
provider or is it a clock for the genpd consumer device?

If the former, couldn't the clock be managed from the ->power_on|off()
callbacks for the genpd provider?

>
> So we need clk_prepare_on/off to guard power on and power off as below:
>
> clk_prepare_on
> power on
> clk_prepare_off
>
> clk_prepare_on
> power off
> clk_prepare_off
>
> Thanks,
> Peng.
>

[...]

Kind regards
Uffe