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Date: Fri, 07 Jun 2019 13:57:57 +0200
From: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To: Stefan Wahren <stefan.wahren@...e.com>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org, f.fainelli@...il.com,
ptesarik@...e.com, sboyd@...nel.org, 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
On Fri, 2019-06-07 at 13:42 +0200, Stefan Wahren wrote:
> Hi Nicolas,
>
> Am 06.06.19 um 16:22 schrieb Nicolas Saenz Julienne:
> > Raspberry Pi's firmware offers and interface though which update it's
> > performance requirements. It allows us to request for specific runtime
> > frequencies, which the firmware might or might not respect, depending on
> > the firmware configuration and thermals.
> >
> > As the maximum and minimum frequencies are configurable in the firmware
> > there is no way to know in advance their values. So the Raspberry Pi
> > cpufreq driver queries them, builds an opp frequency table to then
> > launch cpufreq-dt.
> >
> > Also, as the firmware interface might be configured as a module, making
> > the cpu clock unavailable during init, this implements a full fledged
> > driver, as opposed to most drivers registering cpufreq-dt, which only
> > make use of an init routine.
> >
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> > Acked-by: Eric Anholt <eric@...olt.net>
> >
> > ---
> >
> > Changes since v1:
> > - Remove compatible checks
> > - Add module support, now full fledged driver
> > - Use NULL in clk_get()
> >
> > drivers/cpufreq/Kconfig.arm | 8 +++
> > drivers/cpufreq/Makefile | 1 +
> > drivers/cpufreq/raspberrypi-cpufreq.c | 100 ++++++++++++++++++++++++++
> > 3 files changed, 109 insertions(+)
> > create mode 100644 drivers/cpufreq/raspberrypi-cpufreq.c
> >
> > diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> > index f8129edc145e..5e9204d443ff 100644
> > --- a/drivers/cpufreq/Kconfig.arm
> > +++ b/drivers/cpufreq/Kconfig.arm
> > @@ -133,6 +133,14 @@ config ARM_QCOM_CPUFREQ_HW
> > The driver implements the cpufreq interface for this HW engine.
> > Say Y if you want to support CPUFreq HW.
> >
> > +config ARM_RASPBERRYPI_CPUFREQ
> > + tristate "Raspberry Pi cpufreq support"
> > + depends on CLK_RASPBERRYPI || COMPILE_TEST
> > + help
> > + This adds the CPUFreq driver for Raspberry Pi
> > +
> > + If in doubt, say N.
> > +
> > config ARM_S3C_CPUFREQ
> > bool
> > help
> > diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> > index 689b26c6f949..121c1acb66c0 100644
> > --- a/drivers/cpufreq/Makefile
> > +++ b/drivers/cpufreq/Makefile
> > @@ -64,6 +64,7 @@ obj-$(CONFIG_ARM_PXA2xx_CPUFREQ) += pxa2xx-cpufreq.o
> > obj-$(CONFIG_PXA3xx) += pxa3xx-cpufreq.o
> > obj-$(CONFIG_ARM_QCOM_CPUFREQ_HW) += qcom-cpufreq-hw.o
> > obj-$(CONFIG_ARM_QCOM_CPUFREQ_KRYO) += qcom-cpufreq-kryo.o
> > +obj-$(CONFIG_ARM_RASPBERRYPI_CPUFREQ) += raspberrypi-cpufreq.o
> > obj-$(CONFIG_ARM_S3C2410_CPUFREQ) += s3c2410-cpufreq.o
> > obj-$(CONFIG_ARM_S3C2412_CPUFREQ) += s3c2412-cpufreq.o
> > obj-$(CONFIG_ARM_S3C2416_CPUFREQ) += s3c2416-cpufreq.o
> > 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
> > @@ -0,0 +1,100 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Raspberry Pi cpufreq driver
> > + *
> > + * Copyright (C) 2019, Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/cpu.h>
> > +#include <linux/cpufreq.h>
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pm_opp.h>
> > +
> > +static struct platform_device *cpufreq_dt;
> > +
> > +static int raspberrypi_cpufreq_probe(struct platform_device *pdev)
> > +{
> > + struct device *cpu_dev;
> > + unsigned long min, max;
> > + unsigned long rate;
> > + struct clk *clk;
> > + int ret;
> > +
> > + cpu_dev = get_cpu_device(0);
> > + if (!cpu_dev) {
> > + pr_err("Cannot get CPU for cpufreq driver\n");
> > + return -ENODEV;
> > + }
> > +
> > + clk = clk_get(cpu_dev, NULL);
> > + if (IS_ERR(clk)) {
> > + dev_err(cpu_dev, "Cannot get clock for CPU0\n");
> > + return PTR_ERR(clk);
> > + }
> > +
> > + /*
> > + * The max and min frequencies are configurable in the Raspberry Pi
> > + * firmware, so we query them at runtime
> > + */
> > + min = clk_round_rate(clk, 0);
> > + max = clk_round_rate(clk, ULONG_MAX);
> > + clk_put(clk);
> > +
> > + for (rate = min; rate < max; rate += 100000000) {
> > + ret = dev_pm_opp_add(cpu_dev, rate, 0);
> > + if (ret)
> > + goto remove_opp;
> > + }
>
> i played a little bit with my Raspberry Pi Zero W and this series. Looks
> fine so far.
>
> Sorry for this nitpicking, but i expect user questions about the
> differences between sysfs and vcgencmd measure_clock.
>
> scaling_available_frequencies gives
>
> 699999 799999 899999 999999
>
> but vcgencmd measure_clock return the rounded up values.
>
> I know we shouldn't fake anything, but adding the OPPs rounded up may
> avoid confusion.
>
> Stefan
Agree, I'll change this in v3.
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