/*
 * 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_kcalloc(&pdev->dev, rdesc->n_voltages,
                                     sizeof(struct vctrl_voltage_table),
                                     GFP_KERNEL);
        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 = rdesc->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");