linux-kernel - Re: [PATCH v2 4/7] cpufreq: add driver for Raspbery Pi

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Date:   Thu, 06 Jun 2019 10:36:08 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Viresh Kumar <viresh.kumar@...aro.org>, stefan.wahren@...e.com
Cc:     linux-arm-kernel@...ts.infradead.org, f.fainelli@...il.com,
        ptesarik@...e.com, mturquette@...libre.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        eric@...olt.net, bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        mbrugger@...e.de, ssuloev@...altech.com
Subject: Re: [PATCH v2 4/7] cpufreq: add driver for Raspbery Pi

Quoting Nicolas Saenz Julienne (2019-06-06 10:22:16)
> Hi Stephen,
> Thanks for the review.
> 
> 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 return
> > > EPROBE_DEFER,
> > > + * all the activity is performed in the probe, which may be defered as
> > > well.
> > > + */
> > > +static struct platform_driver raspberrypi_cpufreq_driver = {
> > > +       .driver = {
> > > +               .name = "raspberrypi-cpufreq",
> > > +       },
> > > +       .probe          = raspberrypi_cpufreq_probe,
> > > +       .remove         = raspberrypi_cpufreq_remove,
> > > +};
> > > +module_platform_driver(raspberrypi_cpufreq_driver);
> > 
> > How does this driver probe? Do you have a node in DT named
> > raspberrypi-cpufreq that matches and probes this? I would think this
> > would follow the drivers/cpufreq/cpufreq-dt-platdev.c design where it's
> > an initcall that probes the board compatible string.
> >
> > Or, if it depends on clk-raspberrypi probing, maybe it could create the
> > platform device in that drivers probe function.
> 
> Well you just reviewed that patch :)

Ok. So what's your plan?

> 
> > > +
> > > +MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@...e.de");
> > > +MODULE_DESCRIPTION("Raspberry Pi cpufreq driver");
> > > +MODULE_LICENSE("GPL");
> > > +MODULE_ALIAS("platform:raspberrypi-cpufreq");
> > 
> > I don't think the module alias is needed anymore.
> 
> That's surprising. I remember the driver not being loaded by udev without it.
> 

Maybe I'm wrong. Could be not needed for DT based platform devices with
an OF table.