drivers/iio/dac/dpot-dac.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * IIO DAC emulation driver using a digital potentiometer
   4  *
   5  * Copyright (C) 2016 Axentia Technologies AB
   6  *
   7  * Author: Peter Rosin <peda@axentia.se>
   8  */
   9
  10 /*
  11  * It is assumed that the dpot is used as a voltage divider between the
  12  * current dpot wiper setting and the maximum resistance of the dpot. The
  13  * divided voltage is provided by a vref regulator.
  14  *
  15  *                   .------.
  16  *    .-----------.  |      |
  17  *    | vref      |--'    .---.
  18  *    | regulator |--.    |   |
  19  *    '-----------'  |    | d |
  20  *                   |    | p |
  21  *                   |    | o |  wiper
  22  *                   |    | t |<---------+
  23  *                   |    |   |
  24  *                   |    '---'       dac output voltage
  25  *                   |      |
  26  *                   '------+------------+
  27  */
  28
  29 #include <linux/err.h>
  30 #include <linux/iio/consumer.h>
  31 #include <linux/iio/iio.h>
  32 #include <linux/module.h>
  33 #include <linux/of.h>
  34 #include <linux/platform_device.h>
  35 #include <linux/regulator/consumer.h>
  36
  37 struct dpot_dac {
  38         struct regulator *vref;
  39         struct iio_channel *dpot;
  40         u32 max_ohms;
  41 };
  42
  43 static const struct iio_chan_spec dpot_dac_iio_channel = {
  44         .type = IIO_VOLTAGE,
  45         .info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
  46                             | BIT(IIO_CHAN_INFO_SCALE),
  47         .info_mask_separate_available = BIT(IIO_CHAN_INFO_RAW),
  48         .output = 1,
  49         .indexed = 1,
  50 };
  51
  52 static int dpot_dac_read_raw(struct iio_dev *indio_dev,
  53                              struct iio_chan_spec const *chan,
  54                              int *val, int *val2, long mask)
  55 {
  56         struct dpot_dac *dac = iio_priv(indio_dev);
  57         int ret;
  58         unsigned long long tmp;
  59
  60         switch (mask) {
  61         case IIO_CHAN_INFO_RAW:
  62                 return iio_read_channel_raw(dac->dpot, val);
  63
  64         case IIO_CHAN_INFO_SCALE:
  65                 ret = iio_read_channel_scale(dac->dpot, val, val2);
  66                 switch (ret) {
  67                 case IIO_VAL_FRACTIONAL_LOG2:
  68                         tmp = *val * 1000000000LL;
  69                         do_div(tmp, dac->max_ohms);
  70                         tmp *= regulator_get_voltage(dac->vref) / 1000;
  71                         do_div(tmp, 1000000000LL);
  72                         *val = tmp;
  73                         return ret;
  74                 case IIO_VAL_INT:
  75                         /*
  76                          * Convert integer scale to fractional scale by
  77                          * setting the denominator (val2) to one...
  78                          */
  79                         *val2 = 1;
  80                         ret = IIO_VAL_FRACTIONAL;
  81                         /* ...and fall through. Say it again for GCC. */
  82                         fallthrough;
  83                 case IIO_VAL_FRACTIONAL:
  84                         *val *= regulator_get_voltage(dac->vref) / 1000;
  85                         *val2 *= dac->max_ohms;
  86                         break;
  87                 }
  88
  89                 return ret;
  90         }
  91
  92         return -EINVAL;
  93 }
  94
  95 static int dpot_dac_read_avail(struct iio_dev *indio_dev,
  96                                struct iio_chan_spec const *chan,
  97                                const int **vals, int *type, int *length,
  98                                long mask)
  99 {
 100         struct dpot_dac *dac = iio_priv(indio_dev);
 101
 102         switch (mask) {
 103         case IIO_CHAN_INFO_RAW:
 104                 *type = IIO_VAL_INT;
 105                 return iio_read_avail_channel_raw(dac->dpot, vals, length);
 106         }
 107
 108         return -EINVAL;
 109 }
 110
 111 static int dpot_dac_write_raw(struct iio_dev *indio_dev,
 112                               struct iio_chan_spec const *chan,
 113                               int val, int val2, long mask)
 114 {
 115         struct dpot_dac *dac = iio_priv(indio_dev);
 116
 117         switch (mask) {
 118         case IIO_CHAN_INFO_RAW:
 119                 return iio_write_channel_raw(dac->dpot, val);
 120         }
 121
 122         return -EINVAL;
 123 }
 124
 125 static const struct iio_info dpot_dac_info = {
 126         .read_raw = dpot_dac_read_raw,
 127         .read_avail = dpot_dac_read_avail,
 128         .write_raw = dpot_dac_write_raw,
 129 };
 130
 131 static int dpot_dac_channel_max_ohms(struct iio_dev *indio_dev)
 132 {
 133         struct device *dev = &indio_dev->dev;
 134         struct dpot_dac *dac = iio_priv(indio_dev);
 135         unsigned long long tmp;
 136         int ret;
 137         int val;
 138         int val2;
 139         int max;
 140
 141         ret = iio_read_max_channel_raw(dac->dpot, &max);
 142         if (ret < 0) {
 143                 dev_err(dev, "dpot does not indicate its raw maximum value\n");
 144                 return ret;
 145         }
 146
 147         switch (iio_read_channel_scale(dac->dpot, &val, &val2)) {
 148         case IIO_VAL_INT:
 149                 return max * val;
 150         case IIO_VAL_FRACTIONAL:
 151                 tmp = (unsigned long long)max * val;
 152                 do_div(tmp, val2);
 153                 return tmp;
 154         case IIO_VAL_FRACTIONAL_LOG2:
 155                 tmp = val * 1000000000LL * max >> val2;
 156                 do_div(tmp, 1000000000LL);
 157                 return tmp;
 158         default:
 159                 dev_err(dev, "dpot has a scale that is too weird\n");
 160         }
 161
 162         return -EINVAL;
 163 }
 164
 165 static int dpot_dac_probe(struct platform_device *pdev)
 166 {
 167         struct device *dev = &pdev->dev;
 168         struct iio_dev *indio_dev;
 169         struct dpot_dac *dac;
 170         enum iio_chan_type type;
 171         int ret;
 172
 173         indio_dev = devm_iio_device_alloc(dev, sizeof(*dac));
 174         if (!indio_dev)
 175                 return -ENOMEM;
 176
 177         platform_set_drvdata(pdev, indio_dev);
 178         dac = iio_priv(indio_dev);
 179
 180         indio_dev->name = dev_name(dev);
 181         indio_dev->info = &dpot_dac_info;
 182         indio_dev->modes = INDIO_DIRECT_MODE;
 183         indio_dev->channels = &dpot_dac_iio_channel;
 184         indio_dev->num_channels = 1;
 185
 186         dac->vref = devm_regulator_get(dev, "vref");
 187         if (IS_ERR(dac->vref))
 188                 return dev_err_probe(&pdev->dev, PTR_ERR(dac->vref),
 189                                      "failed to get vref regulator\n");
 190
 191         dac->dpot = devm_iio_channel_get(dev, "dpot");
 192         if (IS_ERR(dac->dpot))
 193                 return dev_err_probe(&pdev->dev, PTR_ERR(dac->dpot),
 194                                      "failed to get dpot input channel\n");
 195
 196         ret = iio_get_channel_type(dac->dpot, &type);
 197         if (ret < 0)
 198                 return ret;
 199
 200         if (type != IIO_RESISTANCE) {
 201                 dev_err(dev, "dpot is of the wrong type\n");
 202                 return -EINVAL;
 203         }
 204
 205         ret = dpot_dac_channel_max_ohms(indio_dev);
 206         if (ret < 0)
 207                 return ret;
 208         dac->max_ohms = ret;
 209
 210         ret = regulator_enable(dac->vref);
 211         if (ret) {
 212                 dev_err(dev, "failed to enable the vref regulator\n");
 213                 return ret;
 214         }
 215
 216         ret = iio_device_register(indio_dev);
 217         if (ret) {
 218                 dev_err(dev, "failed to register iio device\n");
 219                 goto disable_reg;
 220         }
 221
 222         return 0;
 223
 224 disable_reg:
 225         regulator_disable(dac->vref);
 226         return ret;
 227 }
 228
 229 static int dpot_dac_remove(struct platform_device *pdev)
 230 {
 231         struct iio_dev *indio_dev = platform_get_drvdata(pdev);
 232         struct dpot_dac *dac = iio_priv(indio_dev);
 233
 234         iio_device_unregister(indio_dev);
 235         regulator_disable(dac->vref);
 236
 237         return 0;
 238 }
 239
 240 static const struct of_device_id dpot_dac_match[] = {
 241         { .compatible = "dpot-dac" },
 242         { /* sentinel */ }
 243 };
 244 MODULE_DEVICE_TABLE(of, dpot_dac_match);
 245
 246 static struct platform_driver dpot_dac_driver = {
 247         .probe = dpot_dac_probe,
 248         .remove = dpot_dac_remove,
 249         .driver = {
 250                 .name = "iio-dpot-dac",
 251                 .of_match_table = dpot_dac_match,
 252         },
 253 };
 254 module_platform_driver(dpot_dac_driver);
 255
 256 MODULE_DESCRIPTION("DAC emulation driver using a digital potentiometer");
 257 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
 258 MODULE_LICENSE("GPL v2");