Re: [PATCH v2 2/7] clk: bcm283x: add driver interfacing with Raspberry Pi's firmware

[Nicolas Saenz Julienne]

On Thu, 2019-06-06 at 16:22 +0200, Nicolas Saenz Julienne wrote:
> 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@xxxxxxx>
> Acked-by: Eric Anholt <eric@xxxxxxxxxx>
> 
> ---
> 
> 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 | 302 ++++++++++++++++++++++++++++++
>  3 files changed, 310 insertions(+)
>  create mode 100644 drivers/clk/bcm/clk-raspberrypi.c
> 
> diff --git a/drivers/clk/bcm/Kconfig b/drivers/clk/bcm/Kconfig
> index 29ee7b776cd4..a4a2775d65e1 100644
> --- a/drivers/clk/bcm/Kconfig
> +++ b/drivers/clk/bcm/Kconfig
> @@ -64,3 +64,10 @@ 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 002661d39128..eb7159099d82 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-$(CONFIG_ARCH_BCM2835)	+= clk-bcm2835.o
>  obj-$(CONFIG_ARCH_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..b1365cf19f3a
> --- /dev/null
> +++ b/drivers/clk/bcm/clk-raspberrypi.c
> @@ -0,0 +1,302 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Raspberry Pi driver for firmware controlled clocks
> + *
> + * Even though clk-bcm2835 provides an interface to the harware 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@xxxxxxx>
> + */
> +
> +#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) {
> +		dev_err(dev, "Failed to initialize pllb_arm, %d\n", ret);

Sorry Stefan, I missed removing this message. It's done for the next revision.

> +		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@xxxxxxx>");
> +MODULE_DESCRIPTION("Raspberry Pi firmware clock driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:raspberrypi-clk");

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