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

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Date:   Mon, 28 Sep 2020 11:03:51 +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 16:30, Peng Fan <peng.fan@....com> wrote:
>
> > 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?
>
> It is the 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?
>
> Sadly not former.
>
> Our current solution is to add a clock property to the power domain node(NXP ARM SIP
> based power domain driver), and when power_on/off, we enable/disable the clocks.
>
> But we are moving to use SCMI power domain, and leave the clock in Linux,
> Scmi power domain driver is a generic driver, and we are not able to mix clock
> parts in the driver which is bad.
>
> Your patch gives me a light that if we could use notification to let consumer
> device driver do the clock enable/disable for each power on and power off.
> That would be great.

Thanks for clarifying. Let me re-spin the patch to address your points.

[...]

Kind regards
Uffe