drivers/soc/tegra/regulators-tegra20.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Voltage regulators coupler for NVIDIA Tegra20
  * Copyright (C) 2019 GRATE-DRIVER project
  *
  * Voltage constraints borrowed from downstream kernel sources
  * Copyright (C) 2010-2011 NVIDIA Corporation
  */

 #define pr_fmt(fmt)	"tegra voltage-coupler: " fmt

 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/of.h>
 #include <linux/reboot.h>
 #include <linux/regulator/coupler.h>
 #include <linux/regulator/driver.h>
 #include <linux/regulator/machine.h>

 #include <soc/tegra/pmc.h>

 struct tegra_regulator_coupler {
 	struct regulator_coupler coupler;
 	struct regulator_dev *core_rdev;
 	struct regulator_dev *cpu_rdev;
 	struct regulator_dev *rtc_rdev;
 	struct notifier_block reboot_notifier;
 	int core_min_uV, cpu_min_uV;
 	bool sys_reboot_mode_req;
 	bool sys_reboot_mode;
 };

 static inline struct tegra_regulator_coupler *
 to_tegra_coupler(struct regulator_coupler *coupler)
 {
 	return container_of(coupler, struct tegra_regulator_coupler, coupler);
 }

 static int tegra20_core_limit(struct tegra_regulator_coupler *tegra,
 			      struct regulator_dev *core_rdev)
 {
 	int core_min_uV = 0;
 	int core_max_uV;
 	int core_cur_uV;
 	int err;

 	/*
 	 * Tegra20 SoC has critical DVFS-capable devices that are
 	 * permanently-active or active at a boot time, like EMC
 	 * (DRAM controller) or Display controller for example.
 	 *
 	 * The voltage of a CORE SoC power domain shall not be dropped below
 	 * a minimum level, which is determined by device's clock rate.
 	 * This means that we can't fully allow CORE voltage scaling until
 	 * the state of all DVFS-critical CORE devices is synced.
 	 */
 	if (tegra_pmc_core_domain_state_synced() && !tegra->sys_reboot_mode) {
 		pr_info_once("voltage state synced\n");
 		return 0;
 	}

 	if (tegra->core_min_uV > 0)
 		return tegra->core_min_uV;

 	core_cur_uV = regulator_get_voltage_rdev(core_rdev);
 	if (core_cur_uV < 0)
 		return core_cur_uV;

 	core_max_uV = max(core_cur_uV, 1200000);

 	err = regulator_check_voltage(core_rdev, &core_min_uV, &core_max_uV);
 	if (err)
 		return err;

 	/*
 	 * Limit minimum CORE voltage to a value left from bootloader or,
 	 * if it's unreasonably low value, to the most common 1.2v or to
 	 * whatever maximum value defined via board's device-tree.
 	 */
 	tegra->core_min_uV = core_max_uV;

 	pr_info("core voltage initialized to %duV\n", tegra->core_min_uV);

 	return tegra->core_min_uV;
 }

 static int tegra20_core_rtc_max_spread(struct regulator_dev *core_rdev,
 				       struct regulator_dev *rtc_rdev)
 {
 	struct coupling_desc *c_desc = &core_rdev->coupling_desc;
 	struct regulator_dev *rdev;
 	int max_spread;
 	unsigned int i;

 	for (i = 1; i < c_desc->n_coupled; i++) {
 		max_spread = core_rdev->constraints->max_spread[i - 1];
 		rdev = c_desc->coupled_rdevs[i];

 		if (rdev == rtc_rdev && max_spread)
 			return max_spread;
 	}

 	pr_err_once("rtc-core max-spread is undefined in device-tree\n");

 	return 150000;
 }

 static int tegra20_core_rtc_update(struct tegra_regulator_coupler *tegra,
 				   struct regulator_dev *core_rdev,
 				   struct regulator_dev *rtc_rdev,
 				   int cpu_uV, int cpu_min_uV)
 {
 	int core_min_uV, core_max_uV = INT_MAX;
 	int rtc_min_uV, rtc_max_uV = INT_MAX;
 	int core_target_uV;
 	int rtc_target_uV;
 	int max_spread;
 	int core_uV;
 	int rtc_uV;
 	int err;

 	/*
 	 * RTC and CORE voltages should be no more than 170mV from each other,
 	 * CPU should be below RTC and CORE by at least 120mV. This applies
 	 * to all Tegra20 SoC's.
 	 */
 	max_spread = tegra20_core_rtc_max_spread(core_rdev, rtc_rdev);

 	/*
 	 * The core voltage scaling is currently not hooked up in drivers,
 	 * hence we will limit the minimum core voltage to a reasonable value.
 	 * This should be good enough for the time being.
 	 */
 	core_min_uV = tegra20_core_limit(tegra, core_rdev);
 	if (core_min_uV < 0)
 		return core_min_uV;

 	err = regulator_check_voltage(core_rdev, &core_min_uV, &core_max_uV);
 	if (err)
 		return err;

 	err = regulator_check_consumers(core_rdev, &core_min_uV, &core_max_uV,
 					PM_SUSPEND_ON);
 	if (err)
 		return err;

 	core_uV = regulator_get_voltage_rdev(core_rdev);
 	if (core_uV < 0)
 		return core_uV;

 	core_min_uV = max(cpu_min_uV + 125000, core_min_uV);
 	if (core_min_uV > core_max_uV)
 		return -EINVAL;

 	if (cpu_uV + 120000 > core_uV)
 		pr_err("core-cpu voltage constraint violated: %d %d\n",
 		       core_uV, cpu_uV + 120000);

 	rtc_uV = regulator_get_voltage_rdev(rtc_rdev);
 	if (rtc_uV < 0)
 		return rtc_uV;

 	if (cpu_uV + 120000 > rtc_uV)
 		pr_err("rtc-cpu voltage constraint violated: %d %d\n",
 		       rtc_uV, cpu_uV + 120000);

 	if (abs(core_uV - rtc_uV) > 170000)
 		pr_err("core-rtc voltage constraint violated: %d %d\n",
 		       core_uV, rtc_uV);

 	rtc_min_uV = max(cpu_min_uV + 125000, core_min_uV - max_spread);

 	err = regulator_check_voltage(rtc_rdev, &rtc_min_uV, &rtc_max_uV);
 	if (err)
 		return err;

 	while (core_uV != core_min_uV || rtc_uV != rtc_min_uV) {
 		if (core_uV < core_min_uV) {
 			core_target_uV = min(core_uV + max_spread, core_min_uV);
 			core_target_uV = min(rtc_uV + max_spread, core_target_uV);
 		} else {
 			core_target_uV = max(core_uV - max_spread, core_min_uV);
 			core_target_uV = max(rtc_uV - max_spread, core_target_uV);
 		}

 		if (core_uV == core_target_uV)
 			goto update_rtc;

 		err = regulator_set_voltage_rdev(core_rdev,
 						 core_target_uV,
 						 core_max_uV,
 						 PM_SUSPEND_ON);
 		if (err)
 			return err;

 		core_uV = core_target_uV;
 update_rtc:
 		if (rtc_uV < rtc_min_uV) {
 			rtc_target_uV = min(rtc_uV + max_spread, rtc_min_uV);
 			rtc_target_uV = min(core_uV + max_spread, rtc_target_uV);
 		} else {
 			rtc_target_uV = max(rtc_uV - max_spread, rtc_min_uV);
 			rtc_target_uV = max(core_uV - max_spread, rtc_target_uV);
 		}

 		if (rtc_uV == rtc_target_uV)
 			continue;

 		err = regulator_set_voltage_rdev(rtc_rdev,
 						 rtc_target_uV,
 						 rtc_max_uV,
 						 PM_SUSPEND_ON);
 		if (err)
 			return err;

 		rtc_uV = rtc_target_uV;
 	}

 	return 0;
 }

 static int tegra20_core_voltage_update(struct tegra_regulator_coupler *tegra,
 				       struct regulator_dev *cpu_rdev,
 				       struct regulator_dev *core_rdev,
 				       struct regulator_dev *rtc_rdev)
 {
 	int cpu_uV;

 	cpu_uV = regulator_get_voltage_rdev(cpu_rdev);
 	if (cpu_uV < 0)
 		return cpu_uV;

 	return tegra20_core_rtc_update(tegra, core_rdev, rtc_rdev,
 				       cpu_uV, cpu_uV);
 }

 static int tegra20_cpu_voltage_update(struct tegra_regulator_coupler *tegra,
 				      struct regulator_dev *cpu_rdev,
 				      struct regulator_dev *core_rdev,
 				      struct regulator_dev *rtc_rdev)
 {
 	int cpu_min_uV_consumers = 0;
 	int cpu_max_uV = INT_MAX;
 	int cpu_min_uV = 0;
 	int cpu_uV;
 	int err;

 	err = regulator_check_voltage(cpu_rdev, &cpu_min_uV, &cpu_max_uV);
 	if (err)
 		return err;

 	err = regulator_check_consumers(cpu_rdev, &cpu_min_uV, &cpu_max_uV,
 					PM_SUSPEND_ON);
 	if (err)
 		return err;

 	err = regulator_check_consumers(cpu_rdev, &cpu_min_uV_consumers,
 					&cpu_max_uV, PM_SUSPEND_ON);
 	if (err)
 		return err;

 	cpu_uV = regulator_get_voltage_rdev(cpu_rdev);
 	if (cpu_uV < 0)
 		return cpu_uV;

 	/* store boot voltage level */
 	if (!tegra->cpu_min_uV)
 		tegra->cpu_min_uV = cpu_uV;

 	/*
 	 * CPU's regulator may not have any consumers, hence the voltage
 	 * must not be changed in that case because CPU simply won't
 	 * survive the voltage drop if it's running on a higher frequency.
 	 */
 	if (!cpu_min_uV_consumers)
 		cpu_min_uV = cpu_uV;

 	/* restore boot voltage level */
 	if (tegra->sys_reboot_mode)
 		cpu_min_uV = max(cpu_min_uV, tegra->cpu_min_uV);

 	if (cpu_min_uV > cpu_uV) {
 		err = tegra20_core_rtc_update(tegra, core_rdev, rtc_rdev,
 					      cpu_uV, cpu_min_uV);
 		if (err)
 			return err;

 		err = regulator_set_voltage_rdev(cpu_rdev, cpu_min_uV,
 						 cpu_max_uV, PM_SUSPEND_ON);
 		if (err)
 			return err;
 	} else if (cpu_min_uV < cpu_uV)  {
 		err = regulator_set_voltage_rdev(cpu_rdev, cpu_min_uV,
 						 cpu_max_uV, PM_SUSPEND_ON);
 		if (err)
 			return err;

 		err = tegra20_core_rtc_update(tegra, core_rdev, rtc_rdev,
 					      cpu_uV, cpu_min_uV);
 		if (err)
 			return err;
 	}

 	return 0;
 }

 static int tegra20_regulator_balance_voltage(struct regulator_coupler *coupler,
 					     struct regulator_dev *rdev,
 					     suspend_state_t state)
 {
 	struct tegra_regulator_coupler *tegra = to_tegra_coupler(coupler);
 	struct regulator_dev *core_rdev = tegra->core_rdev;
 	struct regulator_dev *cpu_rdev = tegra->cpu_rdev;
 	struct regulator_dev *rtc_rdev = tegra->rtc_rdev;

 	if ((core_rdev != rdev && cpu_rdev != rdev && rtc_rdev != rdev) ||
 	    state != PM_SUSPEND_ON) {
 		pr_err("regulators are not coupled properly\n");
 		return -EINVAL;
 	}

 	tegra->sys_reboot_mode = READ_ONCE(tegra->sys_reboot_mode_req);

 	if (rdev == cpu_rdev)
 		return tegra20_cpu_voltage_update(tegra, cpu_rdev,
 						  core_rdev, rtc_rdev);

 	if (rdev == core_rdev)
 		return tegra20_core_voltage_update(tegra, cpu_rdev,
 						   core_rdev, rtc_rdev);

 	pr_err("changing %s voltage not permitted\n", rdev_get_name(rtc_rdev));

 	return -EPERM;
 }

 static int tegra20_regulator_prepare_reboot(struct tegra_regulator_coupler *tegra,
 					    bool sys_reboot_mode)
 {
 	int err;

 	if (!tegra->core_rdev || !tegra->rtc_rdev || !tegra->cpu_rdev)
 		return 0;

 	WRITE_ONCE(tegra->sys_reboot_mode_req, true);

 	/*
 	 * Some devices use CPU soft-reboot method and in this case we
 	 * should ensure that voltages are sane for the reboot by restoring
 	 * the minimum boot levels.
 	 */
 	err = regulator_sync_voltage_rdev(tegra->cpu_rdev);
 	if (err)
 		return err;

 	err = regulator_sync_voltage_rdev(tegra->core_rdev);
 	if (err)
 		return err;

 	WRITE_ONCE(tegra->sys_reboot_mode_req, sys_reboot_mode);

 	return 0;
 }

 static int tegra20_regulator_reboot(struct notifier_block *notifier,
 				    unsigned long event, void *cmd)
 {
 	struct tegra_regulator_coupler *tegra;
 	int ret;

 	if (event != SYS_RESTART)
 		return NOTIFY_DONE;

 	tegra = container_of(notifier, struct tegra_regulator_coupler,
 			     reboot_notifier);

 	ret = tegra20_regulator_prepare_reboot(tegra, true);

 	return notifier_from_errno(ret);
 }

 static int tegra20_regulator_attach(struct regulator_coupler *coupler,
 				    struct regulator_dev *rdev)
 {
 	struct tegra_regulator_coupler *tegra = to_tegra_coupler(coupler);
 	struct device_node *np = rdev->dev.of_node;

 	if (of_property_read_bool(np, "nvidia,tegra-core-regulator") &&
 	    !tegra->core_rdev) {
 		tegra->core_rdev = rdev;
 		return 0;
 	}

 	if (of_property_read_bool(np, "nvidia,tegra-rtc-regulator") &&
 	    !tegra->rtc_rdev) {
 		tegra->rtc_rdev = rdev;
 		return 0;
 	}

 	if (of_property_read_bool(np, "nvidia,tegra-cpu-regulator") &&
 	    !tegra->cpu_rdev) {
 		tegra->cpu_rdev = rdev;
 		return 0;
 	}

 	return -EINVAL;
 }

 static int tegra20_regulator_detach(struct regulator_coupler *coupler,
 				    struct regulator_dev *rdev)
 {
 	struct tegra_regulator_coupler *tegra = to_tegra_coupler(coupler);

 	/*
 	 * We don't expect regulators to be decoupled during reboot,
 	 * this may race with the reboot handler and shouldn't ever
 	 * happen in practice.
 	 */
 	if (WARN_ON_ONCE(system_state > SYSTEM_RUNNING))
 		return -EPERM;

 	if (tegra->core_rdev == rdev) {
 		tegra->core_rdev = NULL;
 		return 0;
 	}

 	if (tegra->rtc_rdev == rdev) {
 		tegra->rtc_rdev = NULL;
 		return 0;
 	}

 	if (tegra->cpu_rdev == rdev) {
 		tegra->cpu_rdev = NULL;
 		return 0;
 	}

 	return -EINVAL;
 }

 static struct tegra_regulator_coupler tegra20_coupler = {
 	.coupler = {
 		.attach_regulator = tegra20_regulator_attach,
 		.detach_regulator = tegra20_regulator_detach,
 		.balance_voltage = tegra20_regulator_balance_voltage,
 	},
 	.reboot_notifier.notifier_call = tegra20_regulator_reboot,
 };

 static int __init tegra_regulator_coupler_init(void)
 {
 	int err;

 	if (!of_machine_is_compatible("nvidia,tegra20"))
 		return 0;

 	err = register_reboot_notifier(&tegra20_coupler.reboot_notifier);
 	WARN_ON(err);

 	return regulator_coupler_register(&tegra20_coupler.coupler);
 }
 arch_initcall(tegra_regulator_coupler_init);
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* Voltage regulators coupler for NVIDIA Tegra20
	* Copyright (C) 2019 GRATE-DRIVER project
	*
	* Voltage constraints borrowed from downstream kernel sources
	* Copyright (C) 2010-2011 NVIDIA Corporation
	*/

	#define pr_fmt(fmt) "tegra voltage-coupler: " fmt

	#include <linux/init.h>
	#include <linux/kernel.h>
	#include <linux/of.h>
	#include <linux/reboot.h>
	#include <linux/regulator/coupler.h>
	#include <linux/regulator/driver.h>
	#include <linux/regulator/machine.h>

	#include <soc/tegra/pmc.h>

	struct tegra_regulator_coupler {
	struct regulator_coupler coupler;
	struct regulator_dev *core_rdev;
	struct regulator_dev *cpu_rdev;
	struct regulator_dev *rtc_rdev;
	struct notifier_block reboot_notifier;
	int core_min_uV, cpu_min_uV;
	bool sys_reboot_mode_req;
	bool sys_reboot_mode;
	};

	static inline struct tegra_regulator_coupler *
	to_tegra_coupler(struct regulator_coupler *coupler)
	{
	return container_of(coupler, struct tegra_regulator_coupler, coupler);
	}

	static int tegra20_core_limit(struct tegra_regulator_coupler *tegra,
	struct regulator_dev *core_rdev)
	{
	int core_min_uV = 0;
	int core_max_uV;
	int core_cur_uV;
	int err;

	/*
	* Tegra20 SoC has critical DVFS-capable devices that are
	* permanently-active or active at a boot time, like EMC
	* (DRAM controller) or Display controller for example.
	*
	* The voltage of a CORE SoC power domain shall not be dropped below
	* a minimum level, which is determined by device's clock rate.
	* This means that we can't fully allow CORE voltage scaling until
	* the state of all DVFS-critical CORE devices is synced.
	*/
	if (tegra_pmc_core_domain_state_synced() && !tegra->sys_reboot_mode) {
	pr_info_once("voltage state synced\n");
	return 0;
	}

	if (tegra->core_min_uV > 0)
	return tegra->core_min_uV;

	core_cur_uV = regulator_get_voltage_rdev(core_rdev);
	if (core_cur_uV < 0)
	return core_cur_uV;

	core_max_uV = max(core_cur_uV, 1200000);

	err = regulator_check_voltage(core_rdev, &core_min_uV, &core_max_uV);
	if (err)
	return err;

	/*
	* Limit minimum CORE voltage to a value left from bootloader or,
	* if it's unreasonably low value, to the most common 1.2v or to
	* whatever maximum value defined via board's device-tree.
	*/
	tegra->core_min_uV = core_max_uV;

	pr_info("core voltage initialized to %duV\n", tegra->core_min_uV);

	return tegra->core_min_uV;
	}

	static int tegra20_core_rtc_max_spread(struct regulator_dev *core_rdev,
	struct regulator_dev *rtc_rdev)
	{
	struct coupling_desc *c_desc = &core_rdev->coupling_desc;
	struct regulator_dev *rdev;
	int max_spread;
	unsigned int i;

	for (i = 1; i < c_desc->n_coupled; i++) {
	max_spread = core_rdev->constraints->max_spread[i - 1];
	rdev = c_desc->coupled_rdevs[i];

	if (rdev == rtc_rdev && max_spread)
	return max_spread;
	}

	pr_err_once("rtc-core max-spread is undefined in device-tree\n");

	return 150000;
	}

	static int tegra20_core_rtc_update(struct tegra_regulator_coupler *tegra,
	struct regulator_dev *core_rdev,
	struct regulator_dev *rtc_rdev,
	int cpu_uV, int cpu_min_uV)
	{
	int core_min_uV, core_max_uV = INT_MAX;
	int rtc_min_uV, rtc_max_uV = INT_MAX;
	int core_target_uV;
	int rtc_target_uV;
	int max_spread;
	int core_uV;
	int rtc_uV;
	int err;

	/*
	* RTC and CORE voltages should be no more than 170mV from each other,
	* CPU should be below RTC and CORE by at least 120mV. This applies
	* to all Tegra20 SoC's.
	*/
	max_spread = tegra20_core_rtc_max_spread(core_rdev, rtc_rdev);

	/*
	* The core voltage scaling is currently not hooked up in drivers,
	* hence we will limit the minimum core voltage to a reasonable value.
	* This should be good enough for the time being.
	*/
	core_min_uV = tegra20_core_limit(tegra, core_rdev);
	if (core_min_uV < 0)
	return core_min_uV;

	err = regulator_check_voltage(core_rdev, &core_min_uV, &core_max_uV);
	if (err)
	return err;

	err = regulator_check_consumers(core_rdev, &core_min_uV, &core_max_uV,
	PM_SUSPEND_ON);
	if (err)
	return err;

	core_uV = regulator_get_voltage_rdev(core_rdev);
	if (core_uV < 0)
	return core_uV;

	core_min_uV = max(cpu_min_uV + 125000, core_min_uV);
	if (core_min_uV > core_max_uV)
	return -EINVAL;

	if (cpu_uV + 120000 > core_uV)
	pr_err("core-cpu voltage constraint violated: %d %d\n",
	core_uV, cpu_uV + 120000);

	rtc_uV = regulator_get_voltage_rdev(rtc_rdev);
	if (rtc_uV < 0)
	return rtc_uV;

	if (cpu_uV + 120000 > rtc_uV)
	pr_err("rtc-cpu voltage constraint violated: %d %d\n",
	rtc_uV, cpu_uV + 120000);

	if (abs(core_uV - rtc_uV) > 170000)
	pr_err("core-rtc voltage constraint violated: %d %d\n",
	core_uV, rtc_uV);

	rtc_min_uV = max(cpu_min_uV + 125000, core_min_uV - max_spread);

	err = regulator_check_voltage(rtc_rdev, &rtc_min_uV, &rtc_max_uV);
	if (err)
	return err;

	while (core_uV != core_min_uV \|\| rtc_uV != rtc_min_uV) {
	if (core_uV < core_min_uV) {
	core_target_uV = min(core_uV + max_spread, core_min_uV);
	core_target_uV = min(rtc_uV + max_spread, core_target_uV);
	} else {
	core_target_uV = max(core_uV - max_spread, core_min_uV);
	core_target_uV = max(rtc_uV - max_spread, core_target_uV);
	}

	if (core_uV == core_target_uV)
	goto update_rtc;

	err = regulator_set_voltage_rdev(core_rdev,
	core_target_uV,
	core_max_uV,
	PM_SUSPEND_ON);
	if (err)
	return err;

	core_uV = core_target_uV;
	update_rtc:
	if (rtc_uV < rtc_min_uV) {
	rtc_target_uV = min(rtc_uV + max_spread, rtc_min_uV);
	rtc_target_uV = min(core_uV + max_spread, rtc_target_uV);
	} else {
	rtc_target_uV = max(rtc_uV - max_spread, rtc_min_uV);
	rtc_target_uV = max(core_uV - max_spread, rtc_target_uV);
	}

	if (rtc_uV == rtc_target_uV)
	continue;

	err = regulator_set_voltage_rdev(rtc_rdev,
	rtc_target_uV,
	rtc_max_uV,
	PM_SUSPEND_ON);
	if (err)
	return err;

	rtc_uV = rtc_target_uV;
	}

	return 0;
	}

	static int tegra20_core_voltage_update(struct tegra_regulator_coupler *tegra,
	struct regulator_dev *cpu_rdev,
	struct regulator_dev *core_rdev,
	struct regulator_dev *rtc_rdev)
	{
	int cpu_uV;

	cpu_uV = regulator_get_voltage_rdev(cpu_rdev);
	if (cpu_uV < 0)
	return cpu_uV;

	return tegra20_core_rtc_update(tegra, core_rdev, rtc_rdev,
	cpu_uV, cpu_uV);
	}

	static int tegra20_cpu_voltage_update(struct tegra_regulator_coupler *tegra,
	struct regulator_dev *cpu_rdev,
	struct regulator_dev *core_rdev,
	struct regulator_dev *rtc_rdev)
	{
	int cpu_min_uV_consumers = 0;
	int cpu_max_uV = INT_MAX;
	int cpu_min_uV = 0;
	int cpu_uV;
	int err;

	err = regulator_check_voltage(cpu_rdev, &cpu_min_uV, &cpu_max_uV);
	if (err)
	return err;

	err = regulator_check_consumers(cpu_rdev, &cpu_min_uV, &cpu_max_uV,
	PM_SUSPEND_ON);
	if (err)
	return err;

	err = regulator_check_consumers(cpu_rdev, &cpu_min_uV_consumers,
	&cpu_max_uV, PM_SUSPEND_ON);
	if (err)
	return err;

	cpu_uV = regulator_get_voltage_rdev(cpu_rdev);
	if (cpu_uV < 0)
	return cpu_uV;

	/* store boot voltage level */
	if (!tegra->cpu_min_uV)
	tegra->cpu_min_uV = cpu_uV;

	/*
	* CPU's regulator may not have any consumers, hence the voltage
	* must not be changed in that case because CPU simply won't
	* survive the voltage drop if it's running on a higher frequency.
	*/
	if (!cpu_min_uV_consumers)
	cpu_min_uV = cpu_uV;

	/* restore boot voltage level */
	if (tegra->sys_reboot_mode)
	cpu_min_uV = max(cpu_min_uV, tegra->cpu_min_uV);

	if (cpu_min_uV > cpu_uV) {
	err = tegra20_core_rtc_update(tegra, core_rdev, rtc_rdev,
	cpu_uV, cpu_min_uV);
	if (err)
	return err;

	err = regulator_set_voltage_rdev(cpu_rdev, cpu_min_uV,
	cpu_max_uV, PM_SUSPEND_ON);
	if (err)
	return err;
	} else if (cpu_min_uV < cpu_uV) {
	err = regulator_set_voltage_rdev(cpu_rdev, cpu_min_uV,
	cpu_max_uV, PM_SUSPEND_ON);
	if (err)
	return err;

	err = tegra20_core_rtc_update(tegra, core_rdev, rtc_rdev,
	cpu_uV, cpu_min_uV);
	if (err)
	return err;
	}

	return 0;
	}

	static int tegra20_regulator_balance_voltage(struct regulator_coupler *coupler,
	struct regulator_dev *rdev,
	suspend_state_t state)
	{
	struct tegra_regulator_coupler *tegra = to_tegra_coupler(coupler);
	struct regulator_dev *core_rdev = tegra->core_rdev;
	struct regulator_dev *cpu_rdev = tegra->cpu_rdev;
	struct regulator_dev *rtc_rdev = tegra->rtc_rdev;

	if ((core_rdev != rdev && cpu_rdev != rdev && rtc_rdev != rdev) \|\|
	state != PM_SUSPEND_ON) {
	pr_err("regulators are not coupled properly\n");
	return -EINVAL;
	}

	tegra->sys_reboot_mode = READ_ONCE(tegra->sys_reboot_mode_req);

	if (rdev == cpu_rdev)
	return tegra20_cpu_voltage_update(tegra, cpu_rdev,
	core_rdev, rtc_rdev);

	if (rdev == core_rdev)
	return tegra20_core_voltage_update(tegra, cpu_rdev,
	core_rdev, rtc_rdev);

	pr_err("changing %s voltage not permitted\n", rdev_get_name(rtc_rdev));

	return -EPERM;
	}

	static int tegra20_regulator_prepare_reboot(struct tegra_regulator_coupler *tegra,
	bool sys_reboot_mode)
	{
	int err;

	if (!tegra->core_rdev \|\| !tegra->rtc_rdev \|\| !tegra->cpu_rdev)
	return 0;

	WRITE_ONCE(tegra->sys_reboot_mode_req, true);

	/*
	* Some devices use CPU soft-reboot method and in this case we
	* should ensure that voltages are sane for the reboot by restoring
	* the minimum boot levels.
	*/
	err = regulator_sync_voltage_rdev(tegra->cpu_rdev);
	if (err)
	return err;

	err = regulator_sync_voltage_rdev(tegra->core_rdev);
	if (err)
	return err;

	WRITE_ONCE(tegra->sys_reboot_mode_req, sys_reboot_mode);

	return 0;
	}

	static int tegra20_regulator_reboot(struct notifier_block *notifier,
	unsigned long event, void *cmd)
	{
	struct tegra_regulator_coupler *tegra;
	int ret;

	if (event != SYS_RESTART)
	return NOTIFY_DONE;

	tegra = container_of(notifier, struct tegra_regulator_coupler,
	reboot_notifier);

	ret = tegra20_regulator_prepare_reboot(tegra, true);

	return notifier_from_errno(ret);
	}

	static int tegra20_regulator_attach(struct regulator_coupler *coupler,
	struct regulator_dev *rdev)
	{
	struct tegra_regulator_coupler *tegra = to_tegra_coupler(coupler);
	struct device_node *np = rdev->dev.of_node;

	if (of_property_read_bool(np, "nvidia,tegra-core-regulator") &&
	!tegra->core_rdev) {
	tegra->core_rdev = rdev;
	return 0;
	}

	if (of_property_read_bool(np, "nvidia,tegra-rtc-regulator") &&
	!tegra->rtc_rdev) {
	tegra->rtc_rdev = rdev;
	return 0;
	}

	if (of_property_read_bool(np, "nvidia,tegra-cpu-regulator") &&
	!tegra->cpu_rdev) {
	tegra->cpu_rdev = rdev;
	return 0;
	}

	return -EINVAL;
	}

	static int tegra20_regulator_detach(struct regulator_coupler *coupler,
	struct regulator_dev *rdev)
	{
	struct tegra_regulator_coupler *tegra = to_tegra_coupler(coupler);

	/*
	* We don't expect regulators to be decoupled during reboot,
	* this may race with the reboot handler and shouldn't ever
	* happen in practice.
	*/
	if (WARN_ON_ONCE(system_state > SYSTEM_RUNNING))
	return -EPERM;

	if (tegra->core_rdev == rdev) {
	tegra->core_rdev = NULL;
	return 0;
	}

	if (tegra->rtc_rdev == rdev) {
	tegra->rtc_rdev = NULL;
	return 0;
	}

	if (tegra->cpu_rdev == rdev) {
	tegra->cpu_rdev = NULL;
	return 0;
	}

	return -EINVAL;
	}

	static struct tegra_regulator_coupler tegra20_coupler = {
	.coupler = {
	.attach_regulator = tegra20_regulator_attach,
	.detach_regulator = tegra20_regulator_detach,
	.balance_voltage = tegra20_regulator_balance_voltage,
	},
	.reboot_notifier.notifier_call = tegra20_regulator_reboot,
	};

	static int __init tegra_regulator_coupler_init(void)
	{
	int err;

	if (!of_machine_is_compatible("nvidia,tegra20"))
	return 0;

	err = register_reboot_notifier(&tegra20_coupler.reboot_notifier);
	WARN_ON(err);

	return regulator_coupler_register(&tegra20_coupler.coupler);
	}
	arch_initcall(tegra_regulator_coupler_init);