linux-kernel - Re: [RFC 5/5] cpufreq: add driver for Raspbery Pi

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Message-ID: <20190520043953.dsmxnxpggkzq4fnm@vireshk-i7>
Date:   Mon, 20 May 2019 10:09:53 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     stefan.wahren@...e.com, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [RFC 5/5] cpufreq: add driver for Raspbery Pi

On 17-05-19, 17:35, 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.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> ---
>  drivers/cpufreq/Kconfig.arm           |  8 +++
>  drivers/cpufreq/Makefile              |  1 +
>  drivers/cpufreq/raspberrypi-cpufreq.c | 79 +++++++++++++++++++++++++++
>  3 files changed, 88 insertions(+)
>  create mode 100644 drivers/cpufreq/raspberrypi-cpufreq.c
> 
> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> index 179a1d302f48..70e5f13f7632 100644
> --- a/drivers/cpufreq/Kconfig.arm
> +++ b/drivers/cpufreq/Kconfig.arm
> @@ -308,3 +308,11 @@ config ARM_PXA2xx_CPUFREQ
>  	  This add the CPUFreq driver support for Intel PXA2xx SOCs.
>  
>  	  If in doubt, say N.
> +
> +config ARM_RASPBERRYPI_CPUFREQ
> +	tristate "Raspberry Pi cpufreq support"
> +	depends on RASPBERRYPI_FIRMWARE || (RASPBERRYPI_FIRMWARE=n && COMPILE_TEST)

What about:
        depends on RASPBERRYPI_FIRMWARE || COMPILE_TEST

> +	help
> +	  This adds the CPUFreq driver for Raspberry Pi
> +
> +	  If in doubt, say N.
> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> index 689b26c6f949..02678e9b2ff5 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -84,6 +84,7 @@ obj-$(CONFIG_ARM_TEGRA124_CPUFREQ)	+= tegra124-cpufreq.o
>  obj-$(CONFIG_ARM_TEGRA186_CPUFREQ)	+= tegra186-cpufreq.o
>  obj-$(CONFIG_ARM_TI_CPUFREQ)		+= ti-cpufreq.o
>  obj-$(CONFIG_ARM_VEXPRESS_SPC_CPUFREQ)	+= vexpress-spc-cpufreq.o
> +obj-$(CONFIG_ARM_RASPBERRYPI_CPUFREQ) 	+= raspberrypi-cpufreq.o
>  
>  
>  ##################################################################################
> diff --git a/drivers/cpufreq/raspberrypi-cpufreq.c b/drivers/cpufreq/raspberrypi-cpufreq.c
> new file mode 100644
> index 000000000000..53cb3e5a8457
> --- /dev/null
> +++ b/drivers/cpufreq/raspberrypi-cpufreq.c
> @@ -0,0 +1,79 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Raspberry Pi cpufreq driver
> + *
> + * Copyright (C) 2019, Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> + */
> +
> +#include <linux/of.h>
> +#include <linux/clk.h>
> +#include <linux/cpu.h>
> +#include <linux/module.h>
> +#include <linux/pm_opp.h>
> +#include <linux/cpufreq.h>
> +#include <linux/platform_device.h>
> +
> +static const struct of_device_id machines[] __initconst = {
> +	{ .compatible = "raspberrypi,3-model-b-plus" },
> +	{ .compatible = "raspberrypi,3-model-b" },
> +	{ /* sentinel */ }
> +};
> +
> +static int __init raspberrypi_cpufreq_driver_init(void)
> +{
> +	struct platform_device *pdev;
> +	struct cpumask shared_cpus;
> +	struct device *cpu_dev;
> +	struct clk *clk;
> +	long min, max;
> +	long rate;
> +	int ret;
> +
> +	if (!of_match_node(machines, of_root))
> +		return -ENODEV;
> +
> +	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, 0);
> +	if (IS_ERR(clk)) {
> +		dev_err(cpu_dev, "Cannot get clock for CPU0\n");
> +		return PTR_ERR(clk);
> +	}

You want to do a clk_put() somewhere ?

> +
> +	/*
> +	 * 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);
> +
> +	for (rate = min; rate < max; rate += 100000000) {
> +		ret = dev_pm_opp_add(cpu_dev, rate, 0);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	ret = dev_pm_opp_add(cpu_dev, max, 0);
> +	if (ret)
> +		return ret;

On errors, you should remove all previously added OPPs.

> +
> +	cpumask_setall(&shared_cpus);
> +	dev_pm_opp_set_sharing_cpus(cpu_dev, &shared_cpus);

Why are these required? This must be done by the cpufreq-dt driver anyway ?

> +
> +	pdev = platform_device_register_data(NULL, "cpufreq-dt", -1, NULL, 0);
> +	ret = PTR_ERR_OR_ZERO(pdev);
> +	if (ret)
> +		dev_err(cpu_dev, "Failed to create platform device, %d\n", ret);
> +
> +	return ret;
> +}
> +
> +late_initcall(raspberrypi_cpufreq_driver_init);
> +
> +MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@...e.de");
> +MODULE_DESCRIPTION("Raspberry Pi cpufreq driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.21.0

-- 
viresh