[PATCH v3 2/7] clk: bcm283x: add driver interfacing with Raspberry Pi's firmware

Nicolas Saenz Julienne
2019-06-11T18:01:44Z

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>
---

Changes since v2:
- Remove redundant error message
- Rebase to linux next
- Fix spelling
- Fix checkpatch.pl errors

Changes since v1:
- Use BIT()
- Add Kconfig entry, with compile test
- remove prepare/unprepare
- Fix uninitialized init.name in pllb registration
- Add MODULE_ALIAS()
- Use determine_rate() instead of round_rate()
- Add small introduction explaining need for driver

drivers/clk/bcm/Kconfig | 7 +
drivers/clk/bcm/Makefile | 1 +
drivers/clk/bcm/clk-raspberrypi.c | 300 ++++++++++++++++++++++++++++++
3 files changed, 308 insertions(+)
create mode 100644 drivers/clk/bcm/clk-raspberrypi.c

diff --git a/drivers/clk/bcm/Kconfig b/drivers/clk/bcm/Kconfig
index 766a838ad9af..16e508eba6e5 100644
--- a/drivers/clk/bcm/Kconfig
+++ b/drivers/clk/bcm/Kconfig
@@ -74,3 +74,10 @@ 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
diff --git a/drivers/clk/bcm/Makefile b/drivers/clk/bcm/Makefile
index e924f25bc6c8..004e9526d6f6 100644
--- a/drivers/clk/bcm/Makefile
+++ b/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
diff --git a/drivers/clk/bcm/clk-raspberrypi.c b/drivers/clk/bcm/clk-raspberrypi.c
new file mode 100644
index 000000000000..467933767106
--- /dev/null
+++ b/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 0x000000003
+
+#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 = clk,
+ .val = *val,
+ .disable_turbo = 1,
+ };
+ int ret;
+
+ ret = rpi_firmware_property(firmware, tag, &msg, sizeof(msg));
+ if (ret)
+ return ret;
+
+ *val = 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");
--
2.21.0