Re: [PATCH v3 4/7] cpufreq: add driver for Raspbery Pi

[Nicolas Saenz Julienne <nsaenzjulienne@suse.de>]

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On Tue, 2019-06-11 at 19:58 +0200, Nicolas Saenz Julienne wrote:
> 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@suse.de>
> Acked-by: Eric Anholt <eric@anholt.net>
> Reviewed-by: Stephen Boyd <sboyd@kernel.org>
> ---

Changes since v2:
  - Round OPP rates

> 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 | 97 +++++++++++++++++++++++++++
>  3 files changed, 106 insertions(+)
>  create mode 100644 drivers/cpufreq/raspberrypi-cpufreq.c
> 
> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> index 6f65b7f05496..56c31a78c692 100644
> --- a/drivers/cpufreq/Kconfig.arm
> +++ b/drivers/cpufreq/Kconfig.arm
> @@ -142,6 +142,14 @@ 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 7bcda2273d0c..5a6c70d26c98 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -65,6 +65,7 @@ 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..2bc7d9734272
> --- /dev/null
> +++ b/drivers/cpufreq/raspberrypi-cpufreq.c
> @@ -0,0 +1,97 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Raspberry Pi cpufreq driver
> + *
> + * Copyright (C) 2019, Nicolas Saenz Julienne <nsaenzjulienne@suse.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>
> +
> +#define RASPBERRYPI_FREQ_INTERVAL	100000000
> +
> +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 = roundup(clk_round_rate(clk, 0), RASPBERRYPI_FREQ_INTERVAL);
> +	max = roundup(clk_round_rate(clk, ULONG_MAX),
> RASPBERRYPI_FREQ_INTERVAL);
> +	clk_put(clk);
> +
> +	for (rate = min; rate <= max; rate += RASPBERRYPI_FREQ_INTERVAL) {
> +		ret = dev_pm_opp_add(cpu_dev, rate, 0);
> +		if (ret)
> +			goto remove_opp;
> +	}
> +
> +	cpufreq_dt = platform_device_register_simple("cpufreq-dt", -1, NULL, 0);
> +	ret = PTR_ERR_OR_ZERO(cpufreq_dt);
> +	if (ret) {
> +		dev_err(cpu_dev, "Failed to create platform device, %d\n", ret);
> +		goto remove_opp;
> +	}
> +
> +	return 0;
> +
> +remove_opp:
> +	dev_pm_opp_remove_all_dynamic(cpu_dev);
> +
> +	return ret;
> +}
> +
> +static int raspberrypi_cpufreq_remove(struct platform_device *pdev)
> +{
> +	struct device *cpu_dev;
> +
> +	cpu_dev = get_cpu_device(0);
> +	if (cpu_dev)
> +		dev_pm_opp_remove_all_dynamic(cpu_dev);
> +
> +	platform_device_unregister(cpufreq_dt);
> +
> +	return 0;
> +}
> +
> +/*
> + * 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);
> +
> +MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de");
> +MODULE_DESCRIPTION("Raspberry Pi cpufreq driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:raspberrypi-cpufreq");


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