[PATCH v3 0/2] Add imx6q-cpufreq driver support

[PATCH v3 0/2] Add imx6q-cpufreq driver support

[Shawn Guo]

Changes since v2:
 - Fix typo in commit log
 - Put all OPPs in dts and disable 1.2 GHz one for Si revs that do not
   support it in kernel.

Shawn Guo (2):
  cpufreq: add imx6q-cpufreq driver
  ARM: imx: enable imx6q-cpufreq support

 arch/arm/boot/dts/imx6q.dtsi    |   20 ++-
 arch/arm/mach-imx/mach-imx6q.c  |   65 +++++++++
 drivers/cpufreq/Kconfig.arm     |    9 ++
 drivers/cpufreq/Makefile        |    1 +
 drivers/cpufreq/imx6q-cpufreq.c |  296 +++++++++++++++++++++++++++++++++++++++
 5 files changed, 385 insertions(+), 6 deletions(-)
 create mode 100644 drivers/cpufreq/imx6q-cpufreq.c

-- 
1.7.9.5

[PATCH v3 1/2] cpufreq: add imx6q-cpufreq driver

[Shawn Guo]

Add an imx6q-cpufreq driver for Freescale i.MX6Q SoC to handle the
hardware specific frequency and voltage scaling requirements.

The driver supports module build and is instantiated by the platform
device/driver mechanism, so that it will not be instantiated on other
platforms, as IMX is built with multiplatform support.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 drivers/cpufreq/Kconfig.arm     |    9 ++
 drivers/cpufreq/Makefile        |    1 +
 drivers/cpufreq/imx6q-cpufreq.c |  296 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 306 insertions(+)
 create mode 100644 drivers/cpufreq/imx6q-cpufreq.c

diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
index a0b3661..9e628ba 100644
--- a/drivers/cpufreq/Kconfig.arm
+++ b/drivers/cpufreq/Kconfig.arm
@@ -77,6 +77,15 @@ config ARM_EXYNOS5250_CPUFREQ
 	  This adds the CPUFreq driver for Samsung EXYNOS5250
 	  SoC.
 
+config ARM_IMX6Q_CPUFREQ
+	tristate "Freescale i.MX6Q cpufreq support"
+	depends on SOC_IMX6Q
+	depends on REGULATOR_ANATOP
+	help
+	  This adds cpufreq driver support for Freescale i.MX6Q SOC.
+
+	  If in doubt, say N.
+
 config ARM_SPEAR_CPUFREQ
 	bool "SPEAr CPUFreq support"
 	depends on PLAT_SPEAR
diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
index 1f254ec0..31699a0 100644
--- a/drivers/cpufreq/Makefile
+++ b/drivers/cpufreq/Makefile
@@ -49,6 +49,7 @@ obj-$(CONFIG_ARM_EXYNOS_CPUFREQ)	+= exynos-cpufreq.o
 obj-$(CONFIG_ARM_EXYNOS4210_CPUFREQ)	+= exynos4210-cpufreq.o
 obj-$(CONFIG_ARM_EXYNOS4X12_CPUFREQ)	+= exynos4x12-cpufreq.o
 obj-$(CONFIG_ARM_EXYNOS5250_CPUFREQ)	+= exynos5250-cpufreq.o
+obj-$(CONFIG_ARM_IMX6Q_CPUFREQ)		+= imx6q-cpufreq.o
 obj-$(CONFIG_ARM_OMAP2PLUS_CPUFREQ)     += omap-cpufreq.o
 obj-$(CONFIG_ARM_SPEAR_CPUFREQ)		+= spear-cpufreq.o
 
diff --git a/drivers/cpufreq/imx6q-cpufreq.c b/drivers/cpufreq/imx6q-cpufreq.c
new file mode 100644
index 0000000..218d8f1
--- /dev/null
+++ b/drivers/cpufreq/imx6q-cpufreq.c
@@ -0,0 +1,296 @@
+/*
+ * Copyright (C) 2013 Freescale Semiconductor, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/clk.h>
+#include <linux/cpu.h>
+#include <linux/cpufreq.h>
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/opp.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+
+#define PU_SOC_VOLTAGE_NORMAL	1250000
+#define PU_SOC_VOLTAGE_HIGH	1275000
+#define FREQ_1P2_GHZ		1200000000
+
+static struct regulator *arm_reg;
+static struct regulator *pu_reg;
+static struct regulator *soc_reg;
+
+static struct clk *arm_clk;
+static struct clk *pll1_sys_clk;
+static struct clk *pll1_sw_clk;
+static struct clk *step_clk;
+static struct clk *pll2_pfd2_396m_clk;
+
+static struct device *cpu_dev;
+static struct cpufreq_frequency_table *freq_table;
+static unsigned int transition_latency;
+
+static int imx6q_verify_speed(struct cpufreq_policy *policy)
+{
+	return cpufreq_frequency_table_verify(policy, freq_table);
+}
+
+static unsigned int imx6q_get_speed(unsigned int cpu)
+{
+	return clk_get_rate(arm_clk) / 1000;
+}
+
+static int imx6q_set_target(struct cpufreq_policy *policy,
+			    unsigned int target_freq, unsigned int relation)
+{
+	struct cpufreq_freqs freqs;
+	struct opp *opp;
+	unsigned long freq_hz, volt, volt_old;
+	unsigned int index, cpu;
+	int ret;
+
+	ret = cpufreq_frequency_table_target(policy, freq_table, target_freq,
+					     relation, &index);
+	if (ret) {
+		dev_err(cpu_dev, "failed to match target frequency %d: %d\n",
+			target_freq, ret);
+		return ret;
+	}
+
+	freqs.new = freq_table[index].frequency;
+	freq_hz = freqs.new * 1000;
+	freqs.old = clk_get_rate(arm_clk) / 1000;
+
+	if (freqs.old == freqs.new)
+		return 0;
+
+	for_each_online_cpu(cpu) {
+		freqs.cpu = cpu;
+		cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
+	}
+
+	opp = opp_find_freq_ceil(cpu_dev, &freq_hz);
+	if (IS_ERR(opp)) {
+		dev_err(cpu_dev, "failed to find OPP for %ld\n", freq_hz);
+		return PTR_ERR(opp);
+	}
+
+	volt = opp_get_voltage(opp);
+	volt_old = regulator_get_voltage(arm_reg);
+
+	dev_dbg(cpu_dev, "%u MHz, %ld mV --> %u MHz, %ld mV\n",
+		freqs.old / 1000, volt_old / 1000,
+		freqs.new / 1000, volt / 1000);
+
+	/* scaling up?  scale voltage before frequency */
+	if (freqs.new > freqs.old) {
+		ret = regulator_set_voltage_tol(arm_reg, volt, 0);
+		if (ret) {
+			dev_err(cpu_dev, "failed to scale voltage up: %d\n", ret);
+			return ret;
+		}
+
+		/*
+		 * Need to increase vddpu and vddsoc for safety
+		 * if we are about to run at 1.2 GHz.
+		 */
+		if (freqs.new == FREQ_1P2_GHZ / 1000) {
+			regulator_set_voltage_tol(pu_reg,
+					PU_SOC_VOLTAGE_HIGH, 0);
+			regulator_set_voltage_tol(soc_reg,
+					PU_SOC_VOLTAGE_HIGH, 0);
+		}
+	}
+
+	/*
+	 * The setpoints are selected per PLL/PDF frequencies, so we need to
+	 * reprogram PLL for frequency scaling.  The procedure of reprogramming
+	 * PLL1 is as below.
+	 *
+	 *  - Enable pll2_pfd2_396m_clk and reparent pll1_sw_clk to it
+	 *  - Disable pll1_sys_clk and reprogram it
+	 *  - Enable pll1_sys_clk and reparent pll1_sw_clk back to it
+	 *  - Disable pll2_pfd2_396m_clk
+	 */
+	clk_prepare_enable(pll2_pfd2_396m_clk);
+	clk_set_parent(step_clk, pll2_pfd2_396m_clk);
+	clk_set_parent(pll1_sw_clk, step_clk);
+	clk_prepare_enable(pll1_sys_clk);
+	if (freq_hz > clk_get_rate(pll2_pfd2_396m_clk)) {
+		clk_disable_unprepare(pll1_sys_clk);
+		clk_set_rate(pll1_sys_clk, freqs.new * 1000);
+		clk_prepare_enable(pll1_sys_clk);
+		clk_set_parent(pll1_sw_clk, pll1_sys_clk);
+		clk_disable_unprepare(pll2_pfd2_396m_clk);
+	} else {
+		/*
+		 * Disable pll1_sys_clk if pll2_pfd2_396m_clk is sufficient
+		 * to provide the frequency.
+		 */
+		clk_disable_unprepare(pll1_sys_clk);
+	}
+
+	/* Ensure the arm clock divider is what we expect */
+	ret = clk_set_rate(arm_clk, freqs.new * 1000);
+	if (ret) {
+		dev_err(cpu_dev, "failed to set clock rate: %d\n", ret);
+		regulator_set_voltage_tol(arm_reg, volt_old, 0);
+		return ret;
+	}
+
+	/* scaling down?  scale voltage after frequency */
+	if (freqs.new < freqs.old) {
+		ret = regulator_set_voltage_tol(arm_reg, volt, 0);
+		if (ret)
+			dev_warn(cpu_dev, "failed to scale voltage down: %d\n", ret);
+
+		if (freqs.old == FREQ_1P2_GHZ / 1000) {
+			regulator_set_voltage_tol(pu_reg,
+					PU_SOC_VOLTAGE_NORMAL, 0);
+			regulator_set_voltage_tol(soc_reg,
+					PU_SOC_VOLTAGE_NORMAL, 0);
+		}
+	}
+
+	for_each_online_cpu(cpu) {
+		freqs.cpu = cpu;
+		cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
+	}
+
+	return 0;
+}
+
+static int imx6q_cpufreq_init(struct cpufreq_policy *policy)
+{
+	int ret;
+
+	ret = cpufreq_frequency_table_cpuinfo(policy, freq_table);
+	if (ret) {
+		dev_err(cpu_dev, "invalid frequency table: %d\n", ret);
+		return ret;
+	}
+
+	policy->cpuinfo.transition_latency = transition_latency;
+	policy->cur = clk_get_rate(arm_clk) / 1000;
+	policy->shared_type = CPUFREQ_SHARED_TYPE_ANY;
+	cpumask_setall(policy->cpus);
+	cpufreq_frequency_table_get_attr(freq_table, policy->cpu);
+
+	return 0;
+}
+
+static int imx6q_cpufreq_exit(struct cpufreq_policy *policy)
+{
+	cpufreq_frequency_table_put_attr(policy->cpu);
+	return 0;
+}
+
+static struct freq_attr *imx6q_cpufreq_attr[] = {
+	&cpufreq_freq_attr_scaling_available_freqs,
+	NULL,
+};
+
+static struct cpufreq_driver imx6q_cpufreq_driver = {
+	.verify = imx6q_verify_speed,
+	.target = imx6q_set_target,
+	.get = imx6q_get_speed,
+	.init = imx6q_cpufreq_init,
+	.exit = imx6q_cpufreq_exit,
+	.name = "imx6q-cpufreq",
+	.attr = imx6q_cpufreq_attr,
+};
+
+static int imx6q_cpufreq_probe(struct platform_device *pdev)
+{
+	struct device_node *np;
+	int ret;
+
+	cpu_dev = &pdev->dev;
+
+	np = of_find_node_by_path("/cpus/cpu@0");
+	if (!np) {
+		dev_err(cpu_dev, "failed to find cpu0 node\n");
+		return -ENOENT;
+	}
+
+	cpu_dev->of_node = np;
+
+	arm_clk = devm_clk_get(cpu_dev, "arm");
+	pll1_sys_clk = devm_clk_get(cpu_dev, "pll1_sys");
+	pll1_sw_clk = devm_clk_get(cpu_dev, "pll1_sw");
+	step_clk = devm_clk_get(cpu_dev, "step");
+	pll2_pfd2_396m_clk = devm_clk_get(cpu_dev, "pll2_pfd2_396m");
+	if (IS_ERR(arm_clk) || IS_ERR(pll1_sys_clk) || IS_ERR(pll1_sw_clk) ||
+	    IS_ERR(step_clk) || IS_ERR(pll2_pfd2_396m_clk)) {
+		dev_err(cpu_dev, "failed to get clocks\n");
+		ret = -ENOENT;
+		goto put_node;
+	}
+
+	arm_reg = devm_regulator_get(cpu_dev, "arm");
+	pu_reg = devm_regulator_get(cpu_dev, "pu");
+	soc_reg = devm_regulator_get(cpu_dev, "soc");
+	if (!arm_reg || !pu_reg || !soc_reg) {
+		dev_err(cpu_dev, "failed to get regulators\n");
+		ret = -ENOENT;
+		goto put_node;
+	}
+
+	/* We expect an OPP table supplied by platform */
+	ret = opp_get_opp_count(cpu_dev);
+	if (ret < 0) {
+		dev_err(cpu_dev, "no OPP table is found: %d\n", ret);
+		goto put_node;
+	}
+
+	ret = opp_init_cpufreq_table(cpu_dev, &freq_table);
+	if (ret) {
+		dev_err(cpu_dev, "failed to init cpufreq table: %d\n", ret);
+		goto put_node;
+	}
+
+	if (of_property_read_u32(np, "clock-latency", &transition_latency))
+		transition_latency = CPUFREQ_ETERNAL;
+
+	ret = cpufreq_register_driver(&imx6q_cpufreq_driver);
+	if (ret) {
+		dev_err(cpu_dev, "failed register driver: %d\n", ret);
+		goto free_freq_table;
+	}
+
+	of_node_put(np);
+	return 0;
+
+free_freq_table:
+	opp_free_cpufreq_table(cpu_dev, &freq_table);
+put_node:
+	of_node_put(np);
+	return ret;
+}
+
+static int imx6q_cpufreq_remove(struct platform_device *pdev)
+{
+	cpufreq_unregister_driver(&imx6q_cpufreq_driver);
+	opp_free_cpufreq_table(cpu_dev, &freq_table);
+
+	return 0;
+}
+
+static struct platform_driver imx6q_cpufreq_platdrv = {
+	.driver = {
+		.name	= "imx6q-cpufreq",
+		.owner	= THIS_MODULE,
+	},
+	.probe		= imx6q_cpufreq_probe,
+	.remove		= imx6q_cpufreq_remove,
+};
+module_platform_driver(imx6q_cpufreq_platdrv);
+
+MODULE_AUTHOR("Shawn Guo <shawn.guo@linaro.org>");
+MODULE_DESCRIPTION("Freescale i.MX6Q cpufreq driver");
+MODULE_LICENSE("GPL");
-- 
1.7.9.5

[PATCH v3 2/2] ARM: imx: enable imx6q-cpufreq support

[Shawn Guo]

Update operating-points per hardware document and add support for
1 GHz and 1.2 GHz frequencies.

400 MHz, 800 MHz and 1 GHz should be supported by all i.MX6Q chips,
while 1.2 GHz support needs to know from OTP fuse bit.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
---
 arch/arm/boot/dts/imx6q.dtsi   |   20 +++++++++----
 arch/arm/mach-imx/mach-imx6q.c |   65 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+), 6 deletions(-)

diff --git a/arch/arm/boot/dts/imx6q.dtsi b/arch/arm/boot/dts/imx6q.dtsi
index d6265ca..231a32c 100644
--- a/arch/arm/boot/dts/imx6q.dtsi
+++ b/arch/arm/boot/dts/imx6q.dtsi
@@ -38,12 +38,19 @@
 			next-level-cache = <&L2>;
 			operating-points = <
 				/* kHz    uV */
-				792000  1100000
+				1200000 1275000
+				996000  1250000
+				792000  1150000
 				396000  950000
-				198000  850000
 			>;
 			clock-latency = <61036>; /* two CLK32 periods */
-			cpu0-supply = <&reg_cpu>;
+			clocks = <&clks 104>, <&clks 6>, <&clks 16>,
+				 <&clks 17>, <&clks 170>;
+			clock-names = "arm", "pll2_pfd2_396m", "step",
+				      "pll1_sw", "pll1_sys";
+			arm-supply = <&reg_arm>;
+			pu-supply = <&reg_pu>;
+			soc-supply = <&reg_soc>;
 		};
 
 		cpu@1 {
@@ -471,7 +478,7 @@
 					anatop-max-voltage = <2750000>;
 				};
 
-				reg_cpu: regulator-vddcore@140 {
+				reg_arm: regulator-vddcore@140 {
 					compatible = "fsl,anatop-regulator";
 					regulator-name = "cpu";
 					regulator-min-microvolt = <725000>;
@@ -485,7 +492,7 @@
 					anatop-max-voltage = <1450000>;
 				};
 
-				regulator-vddpu@140 {
+				reg_pu: regulator-vddpu@140 {
 					compatible = "fsl,anatop-regulator";
 					regulator-name = "vddpu";
 					regulator-min-microvolt = <725000>;
@@ -499,7 +506,7 @@
 					anatop-max-voltage = <1450000>;
 				};
 
-				regulator-vddsoc@140 {
+				reg_soc: regulator-vddsoc@140 {
 					compatible = "fsl,anatop-regulator";
 					regulator-name = "vddsoc";
 					regulator-min-microvolt = <725000>;
@@ -965,6 +972,7 @@
 			};
 
 			ocotp@021bc000 {
+				compatible = "fsl,imx6q-ocotp";
 				reg = <0x021bc000 0x4000>;
 			};
 
diff --git a/arch/arm/mach-imx/mach-imx6q.c b/arch/arm/mach-imx/mach-imx6q.c
index 4eb1b3a..2f974f5 100644
--- a/arch/arm/mach-imx/mach-imx6q.c
+++ b/arch/arm/mach-imx/mach-imx6q.c
@@ -12,6 +12,7 @@
 
 #include <linux/clk.h>
 #include <linux/clkdev.h>
+#include <linux/cpu.h>
 #include <linux/cpuidle.h>
 #include <linux/delay.h>
 #include <linux/export.h>
@@ -22,6 +23,7 @@
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
+#include <linux/opp.h>
 #include <linux/phy.h>
 #include <linux/regmap.h>
 #include <linux/micrel_phy.h>
@@ -209,9 +211,72 @@ static struct cpuidle_driver imx6q_cpuidle_driver = {
 	.state_count		= 1,
 };
 
+#define OCOTP_CFG3			0x440
+#define OCOTP_CFG3_SPEED_SHIFT		16
+#define OCOTP_CFG3_SPEED_1P2GHZ		0x3
+
+static void __init imx6q_opp_check_1p2ghz(struct device *cpu_dev)
+{
+	struct device_node *np;
+	void __iomem *base;
+	u32 val;
+
+	np = of_find_compatible_node(NULL, NULL, "fsl,imx6q-ocotp");
+	if (!np) {
+		pr_warn("failed to find ocotp node\n");
+		return;
+	}
+
+	base = of_iomap(np, 0);
+	if (!base) {
+		pr_warn("failed to map ocotp\n");
+		goto put_node;
+	}
+
+	val = readl_relaxed(base + OCOTP_CFG3);
+	val >>= OCOTP_CFG3_SPEED_SHIFT;
+	if ((val & 0x3) != OCOTP_CFG3_SPEED_1P2GHZ)
+		if (opp_disable(cpu_dev, 1200000000))
+			pr_warn("failed to disable 1.2 GHz OPP\n");
+
+put_node:
+	of_node_put(np);
+}
+
+static void __init imx6q_opp_init(struct device *cpu_dev)
+{
+	struct device_node *np;
+
+	np = of_find_node_by_path("/cpus/cpu@0");
+	if (!np) {
+		pr_warn("failed to find cpu0 node\n");
+		return;
+	}
+
+	cpu_dev->of_node = np;
+	if (of_init_opp_table(cpu_dev)) {
+		pr_warn("failed to init OPP table\n");
+		goto put_node;
+	}
+
+	imx6q_opp_check_1p2ghz(cpu_dev);
+
+put_node:
+	of_node_put(np);
+}
+
+struct platform_device imx6q_cpufreq_pdev = {
+	.name = "imx6q-cpufreq",
+};
+
 static void __init imx6q_init_late(void)
 {
 	imx_cpuidle_init(&imx6q_cpuidle_driver);
+
+	if (IS_ENABLED(CONFIG_ARM_IMX6Q_CPUFREQ)) {
+		imx6q_opp_init(&imx6q_cpufreq_pdev.dev);
+		platform_device_register(&imx6q_cpufreq_pdev);
+	}
 }
 
 static void __init imx6q_map_io(void)
-- 
1.7.9.5

Re: [PATCH v3 1/2] cpufreq: add imx6q-cpufreq driver

[Eric Nelson]

Hi Shawn,

On 01/14/2013 08:02 AM, Shawn Guo wrote:
> Add an imx6q-cpufreq driver for Freescale i.MX6Q SoC to handle the
> hardware specific frequency and voltage scaling requirements.
>
>
 > <snip>
 >
> --- /dev/null
> +++ b/drivers/cpufreq/imx6q-cpufreq.c
> @@ -0,0 +1,296 @@
>
> <snip>
>
> +
> +static int imx6q_set_target(struct cpufreq_policy *policy,
> +			    unsigned int target_freq, unsigned int relation)
> +{
>
> <snip>
>
> +
> +	/* scaling up?  scale voltage before frequency */
> +	if (freqs.new > freqs.old) {
> +		ret = regulator_set_voltage_tol(arm_reg, volt, 0);
> +		if (ret) {
> +			dev_err(cpu_dev, "failed to scale voltage up: %d\n", ret);
> +			return ret;
> +		}
> +
> +		/*
> +		 * Need to increase vddpu and vddsoc for safety
> +		 * if we are about to run at 1.2 GHz.
> +		 */
> +		if (freqs.new == FREQ_1P2_GHZ / 1000) {
> +			regulator_set_voltage_tol(pu_reg,
> +					PU_SOC_VOLTAGE_HIGH, 0);
> +			regulator_set_voltage_tol(soc_reg,
> +					PU_SOC_VOLTAGE_HIGH, 0);
> +		}

I believe you need a delay here to let the LDOs ramp before changing
the CPU frequency.

According to the i.MX6Q reference manual, with the factory default
step times in PMU_MISC2 and the maximum voltage swing is
	1.25V (1.2GHz) - 0.95V (400MHz) == 0.325V

or 13 steps at 25mV.

The default step time is 0.000021333s (512 clocks at 24MHz), so
the worst case delay needed is ~280uS.

This could also be done in the regulator driver, but that may
require multiple delays if multiple rails are changed.

Regards,


Eric

Re: [PATCH v3 1/2] cpufreq: add imx6q-cpufreq driver

[Shawn Guo]

Hi Eric,

On Mon, Jan 14, 2013 at 08:43:35AM -0700, Eric Nelson wrote:
> >+	/* scaling up?  scale voltage before frequency */
> >+	if (freqs.new > freqs.old) {
> >+		ret = regulator_set_voltage_tol(arm_reg, volt, 0);
> >+		if (ret) {
> >+			dev_err(cpu_dev, "failed to scale voltage up: %d\n", ret);
> >+			return ret;
> >+		}
> >+
> >+		/*
> >+		 * Need to increase vddpu and vddsoc for safety
> >+		 * if we are about to run at 1.2 GHz.
> >+		 */
> >+		if (freqs.new == FREQ_1P2_GHZ / 1000) {
> >+			regulator_set_voltage_tol(pu_reg,
> >+					PU_SOC_VOLTAGE_HIGH, 0);
> >+			regulator_set_voltage_tol(soc_reg,
> >+					PU_SOC_VOLTAGE_HIGH, 0);
> >+		}
> 
> I believe you need a delay here to let the LDOs ramp before changing
> the CPU frequency.
> 
> According to the i.MX6Q reference manual, with the factory default
> step times in PMU_MISC2 and the maximum voltage swing is
> 	1.25V (1.2GHz) - 0.95V (400MHz) == 0.325V
> 
> or 13 steps at 25mV.
> 
> The default step time is 0.000021333s (512 clocks at 24MHz), so
> the worst case delay needed is ~280uS.
> 
> This could also be done in the regulator driver, but that may
> require multiple delays if multiple rails are changed.
> 
I initially thought that regulator driver should take care of it.  But
now I agree with you that we can do it here for the least latency.

Will roll it into v4.  Thanks.

Shawn