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 /* fall through */ 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"); 262