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

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Message-ID: <c967bbfd-ce83-7c89-7f18-98f2c66aa333@i2se.com>
Date:   Fri, 7 Jun 2019 13:42:34 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     mbrugger@...e.de, sboyd@...nel.org, eric@...olt.net,
        f.fainelli@...il.com, bcm-kernel-feedback-list@...adcom.com,
        ptesarik@...e.com, linux-rpi-kernel@...ts.infradead.org,
        ssuloev@...altech.com, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, mturquette@...libre.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] cpufreq: add driver for Raspbery Pi

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