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, and...
  78                          */
  79                         *val2 = 1;
  80                         ret = IIO_VAL_FRACTIONAL;
  81                         fallthrough;
  82                 case IIO_VAL_FRACTIONAL:
  83                         *val *= regulator_get_voltage(dac->vref) / 1000;
  84                         *val2 *= dac->max_ohms;
  85                         break;
  86                 }
  87
  88                 return ret;
  89         }
  90
  91         return -EINVAL;
  92 }
  93
  94 static int dpot_dac_read_avail(struct iio_dev *indio_dev,
  95                                struct iio_chan_spec const *chan,
  96                                const int **vals, int *type, int *length,
  97                                long mask)
  98 {
  99         struct dpot_dac *dac = iio_priv(indio_dev);
 100
 101         switch (mask) {
 102         case IIO_CHAN_INFO_RAW:
 103                 *type = IIO_VAL_INT;
 104                 return iio_read_avail_channel_raw(dac->dpot, vals, length);
 105         }
 106
 107         return -EINVAL;
 108 }
 109
 110 static int dpot_dac_write_raw(struct iio_dev *indio_dev,
 111                               struct iio_chan_spec const *chan,
 112                               int val, int val2, long mask)
 113 {
 114         struct dpot_dac *dac = iio_priv(indio_dev);
 115
 116         switch (mask) {
 117         case IIO_CHAN_INFO_RAW:
 118                 return iio_write_channel_raw(dac->dpot, val);
 119         }
 120
 121         return -EINVAL;
 122 }
 123
 124 static const struct iio_info dpot_dac_info = {
 125         .read_raw = dpot_dac_read_raw,
 126         .read_avail = dpot_dac_read_avail,
 127         .write_raw = dpot_dac_write_raw,
 128 };
 129
 130 static int dpot_dac_channel_max_ohms(struct iio_dev *indio_dev)
 131 {
 132         struct device *dev = &indio_dev->dev;
 133         struct dpot_dac *dac = iio_priv(indio_dev);
 134         unsigned long long tmp;
 135         int ret;
 136         int val;
 137         int val2;
 138         int max;
 139
 140         ret = iio_read_max_channel_raw(dac->dpot, &max);
 141         if (ret < 0) {
 142                 dev_err(dev, "dpot does not indicate its raw maximum value\n");
 143                 return ret;
 144         }
 145
 146         switch (iio_read_channel_scale(dac->dpot, &val, &val2)) {
 147         case IIO_VAL_INT:
 148                 return max * val;
 149         case IIO_VAL_FRACTIONAL:
 150                 tmp = (unsigned long long)max * val;
 151                 do_div(tmp, val2);
 152                 return tmp;
 153         case IIO_VAL_FRACTIONAL_LOG2:
 154                 tmp = val * 1000000000LL * max >> val2;
 155                 do_div(tmp, 1000000000LL);
 156                 return tmp;
 157         default:
 158                 dev_err(dev, "dpot has a scale that is too weird\n");
 159         }
 160
 161         return -EINVAL;
 162 }
 163
 164 static int dpot_dac_probe(struct platform_device *pdev)
 165 {
 166         struct device *dev = &pdev->dev;
 167         struct iio_dev *indio_dev;
 168         struct dpot_dac *dac;
 169         enum iio_chan_type type;
 170         int ret;
 171
 172         indio_dev = devm_iio_device_alloc(dev, sizeof(*dac));
 173         if (!indio_dev)
 174                 return -ENOMEM;
 175
 176         platform_set_drvdata(pdev, indio_dev);
 177         dac = iio_priv(indio_dev);
 178
 179         indio_dev->name = dev_name(dev);
 180         indio_dev->info = &dpot_dac_info;
 181         indio_dev->modes = INDIO_DIRECT_MODE;
 182         indio_dev->channels = &dpot_dac_iio_channel;
 183         indio_dev->num_channels = 1;
 184
 185         dac->vref = devm_regulator_get(dev, "vref");
 186         if (IS_ERR(dac->vref)) {
 187                 if (PTR_ERR(dac->vref) != -EPROBE_DEFER)
 188                         dev_err(&pdev->dev, "failed to get vref regulator\n");
 189                 return PTR_ERR(dac->vref);
 190         }
 191
 192         dac->dpot = devm_iio_channel_get(dev, "dpot");
 193         if (IS_ERR(dac->dpot)) {
 194                 if (PTR_ERR(dac->dpot) != -EPROBE_DEFER)
 195                         dev_err(dev, "failed to get dpot input channel\n");
 196                 return PTR_ERR(dac->dpot);
 197         }
 198
 199         ret = iio_get_channel_type(dac->dpot, &type);
 200         if (ret < 0)
 201                 return ret;
 202
 203         if (type != IIO_RESISTANCE) {
 204                 dev_err(dev, "dpot is of the wrong type\n");
 205                 return -EINVAL;
 206         }
 207
 208         ret = dpot_dac_channel_max_ohms(indio_dev);
 209         if (ret < 0)
 210                 return ret;
 211         dac->max_ohms = ret;
 212
 213         ret = regulator_enable(dac->vref);
 214         if (ret) {
 215                 dev_err(dev, "failed to enable the vref regulator\n");
 216                 return ret;
 217         }
 218
 219         ret = iio_device_register(indio_dev);
 220         if (ret) {
 221                 dev_err(dev, "failed to register iio device\n");
 222                 goto disable_reg;
 223         }
 224
 225         return 0;
 226
 227 disable_reg:
 228         regulator_disable(dac->vref);
 229         return ret;
 230 }
 231
 232 static int dpot_dac_remove(struct platform_device *pdev)
 233 {
 234         struct iio_dev *indio_dev = platform_get_drvdata(pdev);
 235         struct dpot_dac *dac = iio_priv(indio_dev);
 236
 237         iio_device_unregister(indio_dev);
 238         regulator_disable(dac->vref);
 239
 240         return 0;
 241 }
 242
 243 static const struct of_device_id dpot_dac_match[] = {
 244         { .compatible = "dpot-dac" },
 245         { /* sentinel */ }
 246 };
 247 MODULE_DEVICE_TABLE(of, dpot_dac_match);
 248
 249 static struct platform_driver dpot_dac_driver = {
 250         .probe = dpot_dac_probe,
 251         .remove = dpot_dac_remove,
 252         .driver = {
 253                 .name = "iio-dpot-dac",
 254                 .of_match_table = dpot_dac_match,
 255         },
 256 };
 257 module_platform_driver(dpot_dac_driver);
 258
 259 MODULE_DESCRIPTION("DAC emulation driver using a digital potentiometer");
 260 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
 261 MODULE_LICENSE("GPL v2");