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Message-ID: <50edadb7b1b1d74c605d73d48518b5e20638b51a.camel@suse.de>
Subject: Re: [PATCH v2 4/7] cpufreq: add driver for Raspbery Pi
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Stephen Boyd <sboyd@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Viresh Kumar <viresh.kumar@linaro.org>, stefan.wahren@i2se.com
Cc:     f.fainelli@gmail.com, linux-pm@vger.kernel.org,
        mturquette@baylibre.com, ptesarik@suse.com,
        linux-kernel@vger.kernel.org, mbrugger@suse.de, eric@anholt.net,
        bcm-kernel-feedback-list@broadcom.com,
        linux-rpi-kernel@lists.infradead.org, linux-clk@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, ssuloev@orpaltech.com
Date:   Thu, 06 Jun 2019 20:31:47 +0200
In-Reply-To: <20190606182335.1D15F20872@mail.kernel.org>
References: <20190606142255.29454-1-nsaenzjulienne@suse.de>
         <20190606142255.29454-5-nsaenzjulienne@suse.de>
         <20190606170949.4A46720652@mail.kernel.org>
         <eb72a26b55cf17c29df6a7fd3c5def08182e00af.camel@suse.de>
         <20190606173609.2C3952083D@mail.kernel.org>
         <153579ddd7e6bd1e5c860a7a01115e47c78a1442.camel@suse.de>
         <20190606182335.1D15F20872@mail.kernel.org>
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On Thu, 2019-06-06 at 11:23 -0700, Stephen Boyd wrote:
> Quoting Nicolas Saenz Julienne (2019-06-06 11:10:04)
> > On Thu, 2019-06-06 at 10:36 -0700, Stephen Boyd wrote:
> > > Quoting Nicolas Saenz Julienne (2019-06-06 10:22:16)
> > > > Hi Stephen,
> > > > Thanks for the review.
> > > >=20
> > > > On Thu, 2019-06-06 at 10:09 -0700, Stephen Boyd wrote:
> > > > > Quoting Nicolas Saenz Julienne (2019-06-06 07:22:56)
> > > > > > diff --git a/drivers/cpufreq/raspberrypi-cpufreq.c
> > > > > > b/drivers/cpufreq/raspberrypi-cpufreq.c
> > > > > > new file mode 100644
> > > > > > index 000000000000..99b59d5a50aa
> > > > > > --- /dev/null
> > > > > > +++ b/drivers/cpufreq/raspberrypi-cpufreq.c
> > > > > [...]
> > > > > > +
> > > > > > +/*
> > > > > > + * Since the driver depends on clk-raspberrypi, which may retu=
rn
> > > > > > EPROBE_DEFER,
> > > > > > + * all the activity is performed in the probe, which may be de=
fered
> > > > > > as
> > > > > > well.
> > > > > > + */
> > > > > > +static struct platform_driver raspberrypi_cpufreq_driver =3D {
> > > > > > +       .driver =3D {
> > > > > > +               .name =3D "raspberrypi-cpufreq",
> > > > > > +       },
> > > > > > +       .probe          =3D raspberrypi_cpufreq_probe,
> > > > > > +       .remove         =3D raspberrypi_cpufreq_remove,
> > > > > > +};
> > > > > > +module_platform_driver(raspberrypi_cpufreq_driver);
> > > > >=20
> > > > > How does this driver probe? Do you have a node in DT named
> > > > > raspberrypi-cpufreq that matches and probes this? I would think t=
his
> > > > > would follow the drivers/cpufreq/cpufreq-dt-platdev.c design wher=
e
> > > > > it's
> > > > > an initcall that probes the board compatible string.
> > > > >=20
> > > > > Or, if it depends on clk-raspberrypi probing, maybe it could crea=
te
> > > > > the
> > > > > platform device in that drivers probe function.
> > > >=20
> > > > Well you just reviewed that patch :)
> > >=20
> > > Ok. So what's your plan?
> >=20
> > So as discussed previously with the RPi mantainers, they preferred for =
the
> > platform device for raspberrypi-clk to be created by the firmware inter=
face
> > driver. IIRC Stefan said it was more flexible and the approach used wit=
h
> > RPi's
> > hwmon driver already. Also, it's not really clear whether this driver r=
eally
> > fits the device tree as it wouldn't be describing hardware.
> >=20
> > As far as raspberrypi-cpufreq is concerned the max and min frequencies =
are
> > configurable in the firmware. So we can't really integrate cpufreq into=
 the
> > device tree as we need to create the opp table dynamically. Hence the
> > dedicated
> > driver. On top of that the CPU might not have a clock during the init
> > process,
> > as both the firmware interface and raspberrypi-clk can be compiled as
> > modules.
> > So I decided the simplest solution was to create the raspberrypi-cpufre=
q
> > platform device at the end of raspberrypi-clk's probe.
> >=20
> > Once raspberrypi-cpufreq is loaded it queries the min/max frequencies,
> > populates the CPU's opp table and creates an instance of cpufreq-dt. Wh=
ich
> > finally can operate, without the need of any dt info, as opp tables are
> > populated and CPUs have a clock.
> >=20
> > I hope this makes it a little more clear :).
> >=20
>=20
> Yes, thanks. I see that largely follows the commit description so it
> looks OK to me.
>=20

Thanks!


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