regulator: Add driver for voltage controlled regulators

The output voltage of a voltage controlled regulator can be controlled
through the voltage of another regulator. The current version of this
driver assumes that the output voltage is a linear function of the control
voltage.
Signed-off-by: NMatthias Kaehlcke <mka@chromium.org>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/vctrl.txt

+Bindings for Voltage controlled regulators
+==========================================
+
+Required properties:
+--------------------
+- compatible		  : must be "vctrl-regulator".
+- regulator-min-microvolt : smallest voltage consumers may set
+- regulator-max-microvolt : largest voltage consumers may set
+- ctrl-supply		  : The regulator supplying the control voltage.
+- ctrl-voltage-range	  : an array of two integer values describing the range
+			    (min/max) of the control voltage. The values specify
+			    the control voltage needed to generate the corresponding
+			    regulator-min/max-microvolt output voltage.
+
+Optional properties:
+--------------------
+- ovp-threshold-percent	: overvoltage protection (OVP) threshold of the
+			  regulator in percent. Some regulators have an OVP
+			  circuitry which shuts down the regulator when the
+			  actual output voltage deviates beyond a certain
+			  margin from the expected value for a given control
+			  voltage. On larger voltage decreases this can occur
+			  undesiredly since the output voltage does not adjust
+			  inmediately to changes in the control voltage. To
+			  avoid this situation the vctrl driver breaks down
+			  larger voltage decreases into multiple steps, where
+			  each step is within the OVP threshold.
+- min-slew-down-rate	: Describes how slowly the regulator voltage will decay
+			  down in the worst case (lightest expected load).
+			  Specified in uV / us (like main regulator ramp rate).
+			  This value is required when ovp-threshold-percent is
+			  specified.
+
+Example:
+
+	vctrl-reg {
+		compatible = "vctrl-regulator";
+		regulator-name = "vctrl_reg";
+
+		ctrl-supply = <&ctrl_reg>;
+
+		regulator-min-microvolt = <800000>;
+		regulator-max-microvolt = <1500000>;
+
+		ctrl-voltage-range = <200000 500000>;
+
+		min-slew-down-rate = <225>;
+		ovp-threshold-percent = <16>;
+	};

drivers/regulator/Kconfig

@@ -843,6 +843,13 @@ config REGULATOR_TWL4030
 	  This driver supports the voltage regulators provided by
 	  this family of companion chips.
 
+config REGULATOR_VCTRL
+	tristate "Voltage controlled regulators"
+	depends on OF
+	help
+	  This driver provides support for voltage regulators whose output
+	  voltage is controlled by the voltage of another regulator.
+
 config REGULATOR_VEXPRESS
 	tristate "Versatile Express regulators"
 	depends on VEXPRESS_CONFIG

drivers/regulator/Makefile

@@ -105,6 +105,7 @@ obj-$(CONFIG_REGULATOR_TPS65910) += tps65910-regulator.o
 obj-$(CONFIG_REGULATOR_TPS65912) += tps65912-regulator.o
 obj-$(CONFIG_REGULATOR_TPS80031) += tps80031-regulator.o
 obj-$(CONFIG_REGULATOR_TWL4030) += twl-regulator.o twl6030-regulator.o
+obj-$(CONFIG_REGULATOR_VCTRL) += vctrl-regulator.o
 obj-$(CONFIG_REGULATOR_VEXPRESS) += vexpress-regulator.o
 obj-$(CONFIG_REGULATOR_WM831X) += wm831x-dcdc.o
 obj-$(CONFIG_REGULATOR_WM831X) += wm831x-isink.o

drivers/regulator/vctrl-regulator.c

+/*
+ * Driver for voltage controller regulators
+ *
+ * Copyright (C) 2017 Google, Inc.
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/regulator/driver.h>
+#include <linux/regulator/of_regulator.h>
+#include <linux/sort.h>
+
+struct vctrl_voltage_range {
+	int min_uV;
+	int max_uV;
+};
+
+struct vctrl_voltage_ranges {
+	struct vctrl_voltage_range ctrl;
+	struct vctrl_voltage_range out;
+};
+
+struct vctrl_voltage_table {
+	int ctrl;
+	int out;
+	int ovp_min_sel;
+};
+
+struct vctrl_data {
+	struct regulator_dev *rdev;
+	struct regulator_desc desc;
+	struct regulator *ctrl_reg;
+	bool enabled;
+	unsigned int min_slew_down_rate;
+	unsigned int ovp_threshold;
+	struct vctrl_voltage_ranges vrange;
+	struct vctrl_voltage_table *vtable;
+	unsigned int sel;
+};
+
+static int vctrl_calc_ctrl_voltage(struct vctrl_data *vctrl, int out_uV)
+{
+	struct vctrl_voltage_range *ctrl = &vctrl->vrange.ctrl;
+	struct vctrl_voltage_range *out = &vctrl->vrange.out;
+
+	return ctrl->min_uV +
+		DIV_ROUND_CLOSEST_ULL((s64)(out_uV - out->min_uV) *
+				      (ctrl->max_uV - ctrl->min_uV),
+				      out->max_uV - out->min_uV);
+}
+
+static int vctrl_calc_output_voltage(struct vctrl_data *vctrl, int ctrl_uV)
+{
+	struct vctrl_voltage_range *ctrl = &vctrl->vrange.ctrl;
+	struct vctrl_voltage_range *out = &vctrl->vrange.out;
+
+	if (ctrl_uV < 0) {
+		pr_err("vctrl: failed to get control voltage\n");
+		return ctrl_uV;
+	}
+
+	if (ctrl_uV < ctrl->min_uV)
+		return out->min_uV;
+
+	if (ctrl_uV > ctrl->max_uV)
+		return out->max_uV;
+
+	return out->min_uV +
+		DIV_ROUND_CLOSEST_ULL((s64)(ctrl_uV - ctrl->min_uV) *
+				      (out->max_uV - out->min_uV),
+				      ctrl->max_uV - ctrl->min_uV);
+}
+
+static int vctrl_get_voltage(struct regulator_dev *rdev)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+	int ctrl_uV = regulator_get_voltage(vctrl->ctrl_reg);
+
+	return vctrl_calc_output_voltage(vctrl, ctrl_uV);
+}
+
+static int vctrl_set_voltage(struct regulator_dev *rdev,
+			     int req_min_uV, int req_max_uV,
+			     unsigned int *selector)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+	struct regulator *ctrl_reg = vctrl->ctrl_reg;
+	int orig_ctrl_uV = regulator_get_voltage(ctrl_reg);
+	int uV = vctrl_calc_output_voltage(vctrl, orig_ctrl_uV);
+	int ret;
+
+	if (req_min_uV >= uV || !vctrl->ovp_threshold)
+		/* voltage rising or no OVP */
+		return regulator_set_voltage(
+			ctrl_reg,
+			vctrl_calc_ctrl_voltage(vctrl, req_min_uV),
+			vctrl_calc_ctrl_voltage(vctrl, req_max_uV));
+
+	while (uV > req_min_uV) {
+		int max_drop_uV = (uV * vctrl->ovp_threshold) / 100;
+		int next_uV;
+		int next_ctrl_uV;
+		int delay;
+
+		/* Make sure no infinite loop even in crazy cases */
+		if (max_drop_uV == 0)
+			max_drop_uV = 1;
+
+		next_uV = max_t(int, req_min_uV, uV - max_drop_uV);
+		next_ctrl_uV = vctrl_calc_ctrl_voltage(vctrl, next_uV);
+
+		ret = regulator_set_voltage(ctrl_reg,
+					    next_ctrl_uV,
+					    next_ctrl_uV);
+		if (ret)
+			goto err;
+
+		delay = DIV_ROUND_UP(uV - next_uV, vctrl->min_slew_down_rate);
+		usleep_range(delay, delay + DIV_ROUND_UP(delay, 10));
+
+		uV = next_uV;
+	}
+
+	return 0;
+
+err:
+	/* Try to go back to original voltage */
+	regulator_set_voltage(ctrl_reg, orig_ctrl_uV, orig_ctrl_uV);
+
+	return ret;
+}
+
+static int vctrl_get_voltage_sel(struct regulator_dev *rdev)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+
+	return vctrl->sel;
+}
+
+static int vctrl_set_voltage_sel(struct regulator_dev *rdev,
+				 unsigned int selector)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+	struct regulator *ctrl_reg = vctrl->ctrl_reg;
+	unsigned int orig_sel = vctrl->sel;
+	int ret;
+
+	if (selector >= rdev->desc->n_voltages)
+		return -EINVAL;
+
+	if (selector >= vctrl->sel || !vctrl->ovp_threshold) {
+		/* voltage rising or no OVP */
+		ret = regulator_set_voltage(ctrl_reg,
+					    vctrl->vtable[selector].ctrl,
+					    vctrl->vtable[selector].ctrl);
+		if (!ret)
+			vctrl->sel = selector;
+
+		return ret;
+	}
+
+	while (vctrl->sel != selector) {
+		unsigned int next_sel;
+		int delay;
+
+		if (selector >= vctrl->vtable[vctrl->sel].ovp_min_sel)
+			next_sel = selector;
+		else
+			next_sel = vctrl->vtable[vctrl->sel].ovp_min_sel;
+
+		ret = regulator_set_voltage(ctrl_reg,
+					    vctrl->vtable[next_sel].ctrl,
+					    vctrl->vtable[next_sel].ctrl);
+		if (ret) {
+			dev_err(&rdev->dev,
+				"failed to set control voltage to %duV\n",
+				vctrl->vtable[next_sel].ctrl);
+			goto err;
+		}
+		vctrl->sel = next_sel;
+
+		delay = DIV_ROUND_UP(vctrl->vtable[vctrl->sel].out -
+				     vctrl->vtable[next_sel].out,
+				     vctrl->min_slew_down_rate);
+		usleep_range(delay, delay + DIV_ROUND_UP(delay, 10));
+	}
+
+	return 0;
+
+err:
+	if (vctrl->sel != orig_sel) {
+		/* Try to go back to original voltage */
+		if (!regulator_set_voltage(ctrl_reg,
+					   vctrl->vtable[orig_sel].ctrl,
+					   vctrl->vtable[orig_sel].ctrl))
+			vctrl->sel = orig_sel;
+		else
+			dev_warn(&rdev->dev,
+				 "failed to restore original voltage\n");
+	}
+
+	return ret;
+}
+
+static int vctrl_list_voltage(struct regulator_dev *rdev,
+			      unsigned int selector)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+
+	if (selector >= rdev->desc->n_voltages)
+		return -EINVAL;
+
+	return vctrl->vtable[selector].out;
+}
+
+static int vctrl_parse_dt(struct platform_device *pdev,
+			  struct vctrl_data *vctrl)
+{
+	int ret;
+	struct device_node *np = pdev->dev.of_node;
+	u32 pval;
+	u32 vrange_ctrl[2];
+
+	vctrl->ctrl_reg = devm_regulator_get(&pdev->dev, "ctrl");
+	if (IS_ERR(vctrl->ctrl_reg))
+		return PTR_ERR(vctrl->ctrl_reg);
+
+	ret = of_property_read_u32(np, "ovp-threshold-percent", &pval);
+	if (!ret) {
+		vctrl->ovp_threshold = pval;
+		if (vctrl->ovp_threshold > 100) {
+			dev_err(&pdev->dev,
+				"ovp-threshold-percent (%u) > 100\n",
+				vctrl->ovp_threshold);
+			return -EINVAL;
+		}
+	}
+
+	ret = of_property_read_u32(np, "min-slew-down-rate", &pval);
+	if (!ret) {
+		vctrl->min_slew_down_rate = pval;
+
+		/* We use the value as int and as divider; sanity check */
+		if (vctrl->min_slew_down_rate == 0) {
+			dev_err(&pdev->dev,
+				"min-slew-down-rate must not be 0\n");
+			return -EINVAL;
+		} else if (vctrl->min_slew_down_rate > INT_MAX) {
+			dev_err(&pdev->dev, "min-slew-down-rate (%u) too big\n",
+				vctrl->min_slew_down_rate);
+			return -EINVAL;
+		}
+	}
+
+	if (vctrl->ovp_threshold && !vctrl->min_slew_down_rate) {
+		dev_err(&pdev->dev,
+			"ovp-threshold-percent requires min-slew-down-rate\n");
+		return -EINVAL;
+	}
+
+	ret = of_property_read_u32(np, "regulator-min-microvolt", &pval);
+	if (ret) {
+		dev_err(&pdev->dev,
+			"failed to read regulator-min-microvolt: %d\n", ret);
+		return ret;
+	}
+	vctrl->vrange.out.min_uV = pval;
+
+	ret = of_property_read_u32(np, "regulator-max-microvolt", &pval);
+	if (ret) {
+		dev_err(&pdev->dev,
+			"failed to read regulator-max-microvolt: %d\n", ret);
+		return ret;
+	}
+	vctrl->vrange.out.max_uV = pval;
+
+	ret = of_property_read_u32_array(np, "ctrl-voltage-range", vrange_ctrl,
+					 2);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to read ctrl-voltage-range: %d\n",
+			ret);
+		return ret;
+	}
+
+	if (vrange_ctrl[0] >= vrange_ctrl[1]) {
+		dev_err(&pdev->dev, "ctrl-voltage-range is invalid: %d-%d\n",
+			vrange_ctrl[0], vrange_ctrl[1]);
+		return -EINVAL;
+	}
+
+	vctrl->vrange.ctrl.min_uV = vrange_ctrl[0];
+	vctrl->vrange.ctrl.max_uV = vrange_ctrl[1];
+
+	return 0;
+}
+
+static int vctrl_cmp_ctrl_uV(const void *a, const void *b)
+{
+	const struct vctrl_voltage_table *at = a;
+	const struct vctrl_voltage_table *bt = b;
+
+	return at->ctrl - bt->ctrl;
+}
+
+static int vctrl_init_vtable(struct platform_device *pdev)
+{
+	struct vctrl_data *vctrl = platform_get_drvdata(pdev);
+	struct regulator_desc *rdesc = &vctrl->desc;
+	struct regulator *ctrl_reg = vctrl->ctrl_reg;
+	struct vctrl_voltage_range *vrange_ctrl = &vctrl->vrange.ctrl;
+	int n_voltages;
+	int ctrl_uV;
+	int i, idx_vt;
+
+	n_voltages = regulator_count_voltages(ctrl_reg);
+
+	rdesc->n_voltages = n_voltages;
+
+	/* determine number of steps within the range of the vctrl regulator */
+	for (i = 0; i < n_voltages; i++) {
+		ctrl_uV = regulator_list_voltage(ctrl_reg, i);
+
+		if (ctrl_uV < vrange_ctrl->min_uV ||
+		    ctrl_uV > vrange_ctrl->max_uV) {
+			rdesc->n_voltages--;
+			continue;
+		}
+	}
+
+	if (rdesc->n_voltages == 0) {
+		dev_err(&pdev->dev, "invalid configuration\n");
+		return -EINVAL;
+	}
+
+	vctrl->vtable = devm_kmalloc_array(
+		&pdev->dev, sizeof(struct vctrl_voltage_table),
+		rdesc->n_voltages, GFP_KERNEL | __GFP_ZERO);
+	if (!vctrl->vtable)
+		return -ENOMEM;
+
+	/* create mapping control <=> output voltage */
+	for (i = 0, idx_vt = 0; i < n_voltages; i++) {
+		ctrl_uV = regulator_list_voltage(ctrl_reg, i);
+
+		if (ctrl_uV < vrange_ctrl->min_uV ||
+		    ctrl_uV > vrange_ctrl->max_uV)
+			continue;
+
+		vctrl->vtable[idx_vt].ctrl = ctrl_uV;
+		vctrl->vtable[idx_vt].out =
+			vctrl_calc_output_voltage(vctrl, ctrl_uV);
+		idx_vt++;
+	}
+
+	/* we rely on the table to be ordered by ascending voltage */
+	sort(vctrl->vtable, rdesc->n_voltages,
+	     sizeof(struct vctrl_voltage_table), vctrl_cmp_ctrl_uV,
+	     NULL);
+
+	/* pre-calculate OVP-safe downward transitions */
+	for (i = n_voltages - 1; i > 0; i--) {
+		int j;
+		int ovp_min_uV = (vctrl->vtable[i].out *
+				  (100 - vctrl->ovp_threshold)) / 100;
+
+		for (j = 0; j < i; j++) {
+			if (vctrl->vtable[j].out >= ovp_min_uV) {
+				vctrl->vtable[i].ovp_min_sel = j;
+				break;
+			}
+		}
+
+		if (j == i) {
+			dev_warn(&pdev->dev, "switching down from %duV may cause OVP shutdown\n",
+				vctrl->vtable[i].out);
+			/* use next lowest voltage */
+			vctrl->vtable[i].ovp_min_sel = i - 1;
+		}
+	}
+
+	return 0;
+}
+
+static int vctrl_enable(struct regulator_dev *rdev)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+	int ret = regulator_enable(vctrl->ctrl_reg);
+
+	if (!ret)
+		vctrl->enabled = true;
+
+	return ret;
+}
+
+static int vctrl_disable(struct regulator_dev *rdev)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+	int ret = regulator_disable(vctrl->ctrl_reg);
+
+	if (!ret)
+		vctrl->enabled = false;
+
+	return ret;
+}
+
+static int vctrl_is_enabled(struct regulator_dev *rdev)
+{
+	struct vctrl_data *vctrl = rdev_get_drvdata(rdev);
+
+	return vctrl->enabled;
+}
+
+static const struct regulator_ops vctrl_ops_cont = {
+	.enable		  = vctrl_enable,
+	.disable	  = vctrl_disable,
+	.is_enabled	  = vctrl_is_enabled,
+	.get_voltage	  = vctrl_get_voltage,
+	.set_voltage	  = vctrl_set_voltage,
+};
+
+static const struct regulator_ops vctrl_ops_non_cont = {
+	.enable		  = vctrl_enable,
+	.disable	  = vctrl_disable,
+	.is_enabled	  = vctrl_is_enabled,
+	.set_voltage_sel = vctrl_set_voltage_sel,
+	.get_voltage_sel = vctrl_get_voltage_sel,
+	.list_voltage    = vctrl_list_voltage,
+	.map_voltage     = regulator_map_voltage_iterate,
+};
+
+static int vctrl_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct vctrl_data *vctrl;
+	const struct regulator_init_data *init_data;
+	struct regulator_desc *rdesc;
+	struct regulator_config cfg = { };
+	struct vctrl_voltage_range *vrange_ctrl;
+	int ctrl_uV;
+	int ret;
+
+	vctrl = devm_kzalloc(&pdev->dev, sizeof(struct vctrl_data),
+			     GFP_KERNEL);
+	if (!vctrl)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, vctrl);
+
+	ret = vctrl_parse_dt(pdev, vctrl);
+	if (ret)
+		return ret;
+
+	vrange_ctrl = &vctrl->vrange.ctrl;
+
+	rdesc = &vctrl->desc;
+	rdesc->name = "vctrl";
+	rdesc->type = REGULATOR_VOLTAGE;
+	rdesc->owner = THIS_MODULE;
+
+	if ((regulator_get_linear_step(vctrl->ctrl_reg) == 1) ||
+	    (regulator_count_voltages(vctrl->ctrl_reg) == -EINVAL)) {
+		rdesc->continuous_voltage_range = true;
+		rdesc->ops = &vctrl_ops_cont;
+	} else {
+		rdesc->ops = &vctrl_ops_non_cont;
+	}
+
+	init_data = of_get_regulator_init_data(&pdev->dev, np, rdesc);
+	if (!init_data)
+		return -ENOMEM;
+
+	cfg.of_node = np;
+	cfg.dev = &pdev->dev;
+	cfg.driver_data = vctrl;
+	cfg.init_data = init_data;
+
+	if (!rdesc->continuous_voltage_range) {
+		ret = vctrl_init_vtable(pdev);
+		if (ret)
+			return ret;
+
+		ctrl_uV = regulator_get_voltage(vctrl->ctrl_reg);
+		if (ctrl_uV < 0) {
+			dev_err(&pdev->dev, "failed to get control voltage\n");
+			return ctrl_uV;
+		}
+
+		/* determine current voltage selector from control voltage */
+		if (ctrl_uV < vrange_ctrl->min_uV) {
+			vctrl->sel = 0;
+		} else if (ctrl_uV > vrange_ctrl->max_uV) {
+			vctrl->sel = rdesc->n_voltages - 1;
+		} else {
+			int i;
+
+			for (i = 0; i < rdesc->n_voltages; i++) {
+				if (ctrl_uV == vctrl->vtable[i].ctrl) {
+					vctrl->sel = i;
+					break;
+				}
+			}
+		}
+	}
+
+	vctrl->rdev = devm_regulator_register(&pdev->dev, rdesc, &cfg);
+	if (IS_ERR(vctrl->rdev)) {
+		ret = PTR_ERR(vctrl->rdev);
+		dev_err(&pdev->dev, "failed to register regulator: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct of_device_id vctrl_of_match[] = {
+	{ .compatible = "vctrl-regulator", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, vctrl_of_match);
+
+static struct platform_driver vctrl_driver = {
+	.probe		= vctrl_probe,
+	.driver		= {
+		.name		= "vctrl-regulator",
+		.of_match_table = of_match_ptr(vctrl_of_match),
+	},
+};
+
+module_platform_driver(vctrl_driver);
+
+MODULE_DESCRIPTION("Voltage Controlled Regulator Driver");
+MODULE_AUTHOR("Matthias Kaehlcke <mka@chromium.org>");
+MODULE_LICENSE("GPL v2");