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

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Message-ID: <DB6PR0402MB2760B91DB92A5307E12D59BB88360@DB6PR0402MB2760.eurprd04.prod.outlook.com>
Date:   Fri, 25 Sep 2020 14:30:26 +0000
From:   Peng Fan <peng.fan@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
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

> 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,
Peng.
> 
> >
> > 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