[PATCH 4/4] 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>
---

Changes since RFC:
  - Alphabetically ordered relevant stuff
  - Updated Kconfig to select firmware interface
  - Correctly unref clk_dev after use
  - Remove all opps on failure
  - Remove use of dev_pm_opp_set_sharing_cpus()

 drivers/cpufreq/Kconfig.arm           |  8 +++
 drivers/cpufreq/Makefile              |  1 +
 drivers/cpufreq/raspberrypi-cpufreq.c | 84 +++++++++++++++++++++++++++
 3 files changed, 93 insertions(+)
 create mode 100644 drivers/cpufreq/raspberrypi-cpufreq.c

diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
index f8129edc145e..556d432cc826 100644
--- a/drivers/cpufreq/Kconfig.arm
+++ b/drivers/cpufreq/Kconfig.arm
@@ -133,6 +133,14 @@ 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"
+	select RASPBERRYPI_FIRMWARE
+	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 689b26c6f949..121c1acb66c0 100644
--- a/drivers/cpufreq/Makefile
+++ b/drivers/cpufreq/Makefile
@@ -64,6 +64,7 @@ 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..2b3a195a9d37
--- /dev/null
+++ b/drivers/cpufreq/raspberrypi-cpufreq.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Raspberry Pi cpufreq driver
+ *
+ * Copyright (C) 2019, Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
+ */
+
+#include <linux/clk.h>
+#include <linux/cpu.h>
+#include <linux/cpufreq.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/pm_opp.h>
+
+static const struct of_device_id machines[] __initconst = {
+	{ .compatible = "raspberrypi,3-model-b-plus" },
+	{ .compatible = "raspberrypi,3-model-b" },
+	{ .compatible = "raspberrypi,2-model-b" },
+	{ /* sentinel */ }
+};
+
+static int __init raspberrypi_cpufreq_driver_init(void)
+{
+	struct platform_device *pdev;
+	struct device *cpu_dev;
+	unsigned long min, max;
+	unsigned long rate;
+	struct clk *clk;
+	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);
+	clk_put(clk);
+
+	for (rate = min; rate < max; rate += 100000000) {
+		ret = dev_pm_opp_add(cpu_dev, rate, 0);
+		if (ret)
+			goto remove_opp;
+	}
+
+	ret = dev_pm_opp_add(cpu_dev, max, 0);
+	if (ret)
+		goto remove_opp;
+
+	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);
+		goto remove_opp;
+	}
+
+	return 0;
+
+remove_opp:
+	dev_pm_opp_remove_all_dynamic(cpu_dev);
+
+	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