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.

Also, as the firmware interface might be configured as a module, making
the cpu clock unavailable during init, this implements a full fledged
driver, as opposed to most drivers registering cpufreq-dt, which only
make use of an init routine.

Signed-off-by: Nicolas Saenz Julienne <redacted>
Acked-by: Eric Anholt <redacted>

---

Changes since v1:
  - Remove compatible checks
  - Add module support, now full fledged driver
  - Use NULL in clk_get()

 drivers/cpufreq/Kconfig.arm           |   8 +++
 drivers/cpufreq/Makefile              |   1 +
 drivers/cpufreq/raspberrypi-cpufreq.c | 100 ++++++++++++++++++++++++++
 3 files changed, 109 insertions(+)
 create mode 100644 drivers/cpufreq/raspberrypi-cpufreq.c

diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
index f8129edc145e..5e9204d443ff 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"
+	depends on CLK_RASPBERRYPI || COMPILE_TEST
+	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..99b59d5a50aa
--- /dev/null
+++ b/drivers/cpufreq/raspberrypi-cpufreq.c

@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Raspberry Pi cpufreq driver
+ *
+ * Copyright (C) 2019, Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
+ */
+
+#include <linux/clk.h>
+#include <linux/cpu.h>
+#include <linux/cpufreq.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pm_opp.h>
+
+static struct platform_device *cpufreq_dt;
+
+static int raspberrypi_cpufreq_probe(struct platform_device *pdev)
+{
+	struct device *cpu_dev;
+	unsigned long min, max;
+	unsigned long rate;
+	struct clk *clk;
+	int ret;
+
+	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, NULL);
+	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;
+	}