clk: bcm283x: add driver interfacing with Raspberry Pi's firmware

Raspberry Pi's firmware offers an interface though which update it's
clock's frequencies. This is specially useful in order to change the CPU
clock (pllb_arm) which is 'owned' by the firmware and we're unable to
scale using the register interface provided by clk-bcm2835.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/bcm/Kconfig

@@ -72,3 +72,10 @@ config CLK_BCM_SR
 	default ARCH_BCM_IPROC
 	help
 	  Enable common clock framework support for the Broadcom Stingray SoC
+
+config CLK_RASPBERRYPI
+	tristate "Raspberry Pi firmware based clock support"
+	depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)
+	help
+	  Enable common clock framework support for Raspberry Pi's firmware
+	  dependent clocks

drivers/clk/bcm/Makefile

@@ -7,6 +7,7 @@ obj-$(CONFIG_CLK_BCM_KONA)	+= clk-bcm21664.o
 obj-$(CONFIG_COMMON_CLK_IPROC)	+= clk-iproc-armpll.o clk-iproc-pll.o clk-iproc-asiu.o
 obj-$(CONFIG_CLK_BCM2835)	+= clk-bcm2835.o
 obj-$(CONFIG_CLK_BCM2835)	+= clk-bcm2835-aux.o
+obj-$(CONFIG_CLK_RASPBERRYPI)	+= clk-raspberrypi.o
 obj-$(CONFIG_ARCH_BCM_53573)	+= clk-bcm53573-ilp.o
 obj-$(CONFIG_CLK_BCM_CYGNUS)	+= clk-cygnus.o
 obj-$(CONFIG_CLK_BCM_HR2)	+= clk-hr2.o

drivers/clk/bcm/clk-raspberrypi.c

@@ -0,0 +1,300 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Raspberry Pi driver for firmware controlled clocks
+ *
+ * Even though clk-bcm2835 provides an interface to the hardware registers for
+ * the system clocks we've had to factor out 'pllb' as the firmware 'owns' it.
+ * We're not allowed to change it directly as we might race with the
+ * over-temperature and under-voltage protections provided by the firmware.
+ *
+ * Copyright (C) 2019 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
+ */
+
+#include <linux/clkdev.h>
+#include <linux/clk-provider.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include <soc/bcm2835/raspberrypi-firmware.h>
+
+#define RPI_FIRMWARE_ARM_CLK_ID		0x00000003
+
+#define RPI_FIRMWARE_STATE_ENABLE_BIT	BIT(0)
+#define RPI_FIRMWARE_STATE_WAIT_BIT	BIT(1)
+
+/*
+ * Even though the firmware interface alters 'pllb' the frequencies are
+ * provided as per 'pllb_arm'. We need to scale before passing them trough.
+ */
+#define RPI_FIRMWARE_PLLB_ARM_DIV_RATE	2
+
+#define A2W_PLL_FRAC_BITS		20
+
+struct raspberrypi_clk {
+	struct device *dev;
+	struct rpi_firmware *firmware;
+
+	unsigned long min_rate;
+	unsigned long max_rate;
+
+	struct clk_hw pllb;
+	struct clk_hw *pllb_arm;
+	struct clk_lookup *pllb_arm_lookup;
+};
+
+/*
+ * Structure of the message passed to Raspberry Pi's firmware in order to
+ * change clock rates. The 'disable_turbo' option is only available to the ARM
+ * clock (pllb) which we enable by default as turbo mode will alter multiple
+ * clocks at once.
+ *
+ * Even though we're able to access the clock registers directly we're bound to
+ * use the firmware interface as the firmware ultimately takes care of
+ * mitigating overheating/undervoltage situations and we would be changing
+ * frequencies behind his back.
+ *
+ * For more information on the firmware interface check:
+ * https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface
+ */
+struct raspberrypi_firmware_prop {
+	__le32 id;
+	__le32 val;
+	__le32 disable_turbo;
+} __packed;
+
+static int raspberrypi_clock_property(struct rpi_firmware *firmware, u32 tag,
+				      u32 clk, u32 *val)
+{
+	struct raspberrypi_firmware_prop msg = {
+		.id = cpu_to_le32(clk),
+		.val = cpu_to_le32(*val),
+		.disable_turbo = cpu_to_le32(1),
+	};
+	int ret;
+
+	ret = rpi_firmware_property(firmware, tag, &msg, sizeof(msg));
+	if (ret)
+		return ret;
+
+	*val = le32_to_cpu(msg.val);
+
+	return 0;
+}
+
+static int raspberrypi_fw_pll_is_on(struct clk_hw *hw)
+{
+	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
+						   pllb);
+	u32 val = 0;
+	int ret;
+
+	ret = raspberrypi_clock_property(rpi->firmware,
+					 RPI_FIRMWARE_GET_CLOCK_STATE,
+					 RPI_FIRMWARE_ARM_CLK_ID, &val);
+	if (ret)
+		return 0;
+
+	return !!(val & RPI_FIRMWARE_STATE_ENABLE_BIT);
+}
+
+
+static unsigned long raspberrypi_fw_pll_get_rate(struct clk_hw *hw,
+						 unsigned long parent_rate)
+{
+	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
+						   pllb);
+	u32 val = 0;
+	int ret;
+
+	ret = raspberrypi_clock_property(rpi->firmware,
+					 RPI_FIRMWARE_GET_CLOCK_RATE,
+					 RPI_FIRMWARE_ARM_CLK_ID,
+					 &val);
+	if (ret)
+		return ret;
+
+	return val * RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
+}
+
+static int raspberrypi_fw_pll_set_rate(struct clk_hw *hw, unsigned long rate,
+				       unsigned long parent_rate)
+{
+	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
+						   pllb);
+	u32 new_rate = rate / RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
+	int ret;
+
+	ret = raspberrypi_clock_property(rpi->firmware,
+					 RPI_FIRMWARE_SET_CLOCK_RATE,
+					 RPI_FIRMWARE_ARM_CLK_ID,
+					 &new_rate);
+	if (ret)
+		dev_err_ratelimited(rpi->dev, "Failed to change %s frequency: %d",
+				    clk_hw_get_name(hw), ret);
+
+	return ret;
+}
+
+/*
+ * Sadly there is no firmware rate rounding interface. We borrowed it from
+ * clk-bcm2835.
+ */
+static int raspberrypi_pll_determine_rate(struct clk_hw *hw,
+					  struct clk_rate_request *req)
+{
+	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
+						   pllb);
+	u64 div, final_rate;
+	u32 ndiv, fdiv;
+
+	/* We can't use req->rate directly as it would overflow */
+	final_rate = clamp(req->rate, rpi->min_rate, rpi->max_rate);
+
+	div = (u64)final_rate << A2W_PLL_FRAC_BITS;
+	do_div(div, req->best_parent_rate);
+
+	ndiv = div >> A2W_PLL_FRAC_BITS;
+	fdiv = div & ((1 << A2W_PLL_FRAC_BITS) - 1);
+
+	final_rate = ((u64)req->best_parent_rate *
+					((ndiv << A2W_PLL_FRAC_BITS) + fdiv));
+
+	req->rate = final_rate >> A2W_PLL_FRAC_BITS;
+
+	return 0;
+}
+
+static const struct clk_ops raspberrypi_firmware_pll_clk_ops = {
+	.is_prepared = raspberrypi_fw_pll_is_on,
+	.recalc_rate = raspberrypi_fw_pll_get_rate,
+	.set_rate = raspberrypi_fw_pll_set_rate,
+	.determine_rate = raspberrypi_pll_determine_rate,
+};
+
+static int raspberrypi_register_pllb(struct raspberrypi_clk *rpi)
+{
+	u32 min_rate = 0, max_rate = 0;
+	struct clk_init_data init;
+	int ret;
+
+	memset(&init, 0, sizeof(init));
+
+	/* All of the PLLs derive from the external oscillator. */
+	init.parent_names = (const char *[]){ "osc" };
+	init.num_parents = 1;
+	init.name = "pllb";
+	init.ops = &raspberrypi_firmware_pll_clk_ops;
+	init.flags = CLK_GET_RATE_NOCACHE | CLK_IGNORE_UNUSED;
+
+	/* Get min & max rates set by the firmware */
+	ret = raspberrypi_clock_property(rpi->firmware,
+					 RPI_FIRMWARE_GET_MIN_CLOCK_RATE,
+					 RPI_FIRMWARE_ARM_CLK_ID,
+					 &min_rate);
+	if (ret) {
+		dev_err(rpi->dev, "Failed to get %s min freq: %d\n",
+			init.name, ret);
+		return ret;
+	}
+
+	ret = raspberrypi_clock_property(rpi->firmware,
+					 RPI_FIRMWARE_GET_MAX_CLOCK_RATE,
+					 RPI_FIRMWARE_ARM_CLK_ID,
+					 &max_rate);
+	if (ret) {
+		dev_err(rpi->dev, "Failed to get %s max freq: %d\n",
+			init.name, ret);
+		return ret;
+	}
+
+	if (!min_rate || !max_rate) {
+		dev_err(rpi->dev, "Unexpected frequency range: min %u, max %u\n",
+			min_rate, max_rate);
+		return -EINVAL;
+	}
+
+	dev_info(rpi->dev, "CPU frequency range: min %u, max %u\n",
+		 min_rate, max_rate);
+
+	rpi->min_rate = min_rate * RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
+	rpi->max_rate = max_rate * RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
+
+	rpi->pllb.init = &init;
+
+	return devm_clk_hw_register(rpi->dev, &rpi->pllb);
+}
+
+static int raspberrypi_register_pllb_arm(struct raspberrypi_clk *rpi)
+{
+	rpi->pllb_arm = clk_hw_register_fixed_factor(rpi->dev,
+				"pllb_arm", "pllb",
+				CLK_SET_RATE_PARENT | CLK_GET_RATE_NOCACHE,
+				1, 2);
+	if (IS_ERR(rpi->pllb_arm)) {
+		dev_err(rpi->dev, "Failed to initialize pllb_arm\n");
+		return PTR_ERR(rpi->pllb_arm);
+	}
+
+	rpi->pllb_arm_lookup = clkdev_hw_create(rpi->pllb_arm, NULL, "cpu0");
+	if (!rpi->pllb_arm_lookup) {
+		dev_err(rpi->dev, "Failed to initialize pllb_arm_lookup\n");
+		clk_hw_unregister_fixed_factor(rpi->pllb_arm);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static int raspberrypi_clk_probe(struct platform_device *pdev)
+{
+	struct device_node *firmware_node;
+	struct device *dev = &pdev->dev;
+	struct rpi_firmware *firmware;
+	struct raspberrypi_clk *rpi;
+	int ret;
+
+	firmware_node = of_find_compatible_node(NULL, NULL,
+					"raspberrypi,bcm2835-firmware");
+	if (!firmware_node) {
+		dev_err(dev, "Missing firmware node\n");
+		return -ENOENT;
+	}
+
+	firmware = rpi_firmware_get(firmware_node);
+	of_node_put(firmware_node);
+	if (!firmware)
+		return -EPROBE_DEFER;
+
+	rpi = devm_kzalloc(dev, sizeof(*rpi), GFP_KERNEL);
+	if (!rpi)
+		return -ENOMEM;
+
+	rpi->dev = dev;
+	rpi->firmware = firmware;
+
+	ret = raspberrypi_register_pllb(rpi);
+	if (ret) {
+		dev_err(dev, "Failed to initialize pllb, %d\n", ret);
+		return ret;
+	}
+
+	ret = raspberrypi_register_pllb_arm(rpi);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static struct platform_driver raspberrypi_clk_driver = {
+	.driver = {
+		.name = "raspberrypi-clk",
+	},
+	.probe          = raspberrypi_clk_probe,
+};
+module_platform_driver(raspberrypi_clk_driver);
+
+MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
+MODULE_DESCRIPTION("Raspberry Pi firmware clock driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:raspberrypi-clk");