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: Matthias Kaehlcke <mka@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

4 files changed, 603 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/regulator/vctrl.txt b/Documentation/devicetree/bindings/regulator/vctrl.txt
new file mode 100644
index 000000000000..601328d7fdbb
--- /dev/null
+++ b/Documentation/devicetree/bindings/regulator/vctrl.txt
@@ -0,0 +1,49 @@
+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>;
+        };
diff --git a/drivers/regulator/Kconfig b/drivers/regulator/Kconfig
index 936f7ccc9736..da83a3abe288 100644
--- a/drivers/regulator/Kconfig
+++ b/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
diff --git a/drivers/regulator/Makefile b/drivers/regulator/Makefile
index 14294692beb9..e246e148a7f9 100644
--- a/drivers/regulator/Makefile
+++ b/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
diff --git a/drivers/regulator/vctrl-regulator.c b/drivers/regulator/vctrl-regulator.c
new file mode 100644
index 000000000000..6baadef0ed74
--- /dev/null
+++ b/drivers/regulator/vctrl-regulator.c
@@ -0,0 +1,546 @@
+/*
+ * 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");