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

[Nicolas Saenz Julienne]

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@xxxxxxx>
> > Acked-by: Eric Anholt <eric@xxxxxxxxxx>
> > 
> > ---
> > 
> > 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@xxxxxxx>
> > + */
> > +
> > +#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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