[RFC 5/5] cpufreq: add driver for Raspbery Pi

[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.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
---
 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)
+	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@xxxxxxx>
+ */
+
+#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);
+	}
+
+	/*
+	 * 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;
+
+	cpumask_setall(&shared_cpus);
+	dev_pm_opp_set_sharing_cpus(cpu_dev, &shared_cpus);
+
+	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@xxxxxxx");
+MODULE_DESCRIPTION("Raspberry Pi cpufreq driver");
+MODULE_LICENSE("GPL v2");
-- 
2.21.0