linux-kernel - Re: [RFC v2 5/5] cpufreq: add driver for Raspbery Pi

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Date:   Mon, 20 May 2019 14:30:51 +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: [RFC v2 5/5] cpufreq: add driver for Raspbery Pi

On 20.05.19 12:47, 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 | 83 +++++++++++++++++++++++++++
>  3 files changed, 92 insertions(+)
>  create mode 100644 drivers/cpufreq/raspberrypi-cpufreq.c
>
> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> index 179a1d302f48..f6eba7ae50d0 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 || COMPILE_TEST

The driver doesn't really require the firmware driver to compile, how about:

select RASPBERRYPI_FIRMWARE

> +	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..a85988867d56
> --- /dev/null
> +++ b/drivers/cpufreq/raspberrypi-cpufreq.c
> @@ -0,0 +1,83 @@
> +// 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 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);

I suggest use the expected clock ID.