src/kernel/linux/v4.19/drivers/cpufreq/tango-cpufreq.c

#include <linux/of.h>
#include <linux/cpu.h>
#include <linux/clk.h>
#include <linux/pm_opp.h>
#include <linux/platform_device.h>

static const struct of_device_id machines[] __initconst = {
	{ .compatible = "sigma,tango4" },
	{ /* sentinel */ }
};

static int __init tango_cpufreq_init(void)
{
	struct device *cpu_dev = get_cpu_device(0);
	unsigned long max_freq;
	struct clk *cpu_clk;
	void *res;

	if (!of_match_node(machines, of_root))
		return -ENODEV;

	cpu_clk = clk_get(cpu_dev, NULL);
	if (IS_ERR(cpu_clk))
		return -ENODEV;

	max_freq = clk_get_rate(cpu_clk);

	dev_pm_opp_add(cpu_dev, max_freq / 1, 0);
	dev_pm_opp_add(cpu_dev, max_freq / 2, 0);
	dev_pm_opp_add(cpu_dev, max_freq / 3, 0);
	dev_pm_opp_add(cpu_dev, max_freq / 5, 0);
	dev_pm_opp_add(cpu_dev, max_freq / 9, 0);

	res = platform_device_register_data(NULL, "cpufreq-dt", -1, NULL, 0);

	return PTR_ERR_OR_ZERO(res);
}
device_initcall(tango_cpufreq_init);