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
dpot_dac_read_raw(struct iio_dev * indio_dev,struct iio_chan_spec const * chan,int * val,int * val2,long mask)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
dpot_dac_read_avail(struct iio_dev * indio_dev,struct iio_chan_spec const * chan,const int ** vals,int * type,int * length,long mask)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
dpot_dac_write_raw(struct iio_dev * indio_dev,struct iio_chan_spec const * chan,int val,int val2,long mask)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
dpot_dac_channel_max_ohms(struct iio_dev * indio_dev)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
dpot_dac_probe(struct platform_device * pdev)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->dev.parent = 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 if (PTR_ERR(dac->vref) != -EPROBE_DEFER)
189 dev_err(&pdev->dev, "failed to get vref regulator\n");
190 return PTR_ERR(dac->vref);
191 }
192
193 dac->dpot = devm_iio_channel_get(dev, "dpot");
194 if (IS_ERR(dac->dpot)) {
195 if (PTR_ERR(dac->dpot) != -EPROBE_DEFER)
196 dev_err(dev, "failed to get dpot input channel\n");
197 return PTR_ERR(dac->dpot);
198 }
199
200 ret = iio_get_channel_type(dac->dpot, &type);
201 if (ret < 0)
202 return ret;
203
204 if (type != IIO_RESISTANCE) {
205 dev_err(dev, "dpot is of the wrong type\n");
206 return -EINVAL;
207 }
208
209 ret = dpot_dac_channel_max_ohms(indio_dev);
210 if (ret < 0)
211 return ret;
212 dac->max_ohms = ret;
213
214 ret = regulator_enable(dac->vref);
215 if (ret) {
216 dev_err(dev, "failed to enable the vref regulator\n");
217 return ret;
218 }
219
220 ret = iio_device_register(indio_dev);
221 if (ret) {
222 dev_err(dev, "failed to register iio device\n");
223 goto disable_reg;
224 }
225
226 return 0;
227
228 disable_reg:
229 regulator_disable(dac->vref);
230 return ret;
231 }
232
dpot_dac_remove(struct platform_device * pdev)233 static int dpot_dac_remove(struct platform_device *pdev)
234 {
235 struct iio_dev *indio_dev = platform_get_drvdata(pdev);
236 struct dpot_dac *dac = iio_priv(indio_dev);
237
238 iio_device_unregister(indio_dev);
239 regulator_disable(dac->vref);
240
241 return 0;
242 }
243
244 static const struct of_device_id dpot_dac_match[] = {
245 { .compatible = "dpot-dac" },
246 { /* sentinel */ }
247 };
248 MODULE_DEVICE_TABLE(of, dpot_dac_match);
249
250 static struct platform_driver dpot_dac_driver = {
251 .probe = dpot_dac_probe,
252 .remove = dpot_dac_remove,
253 .driver = {
254 .name = "iio-dpot-dac",
255 .of_match_table = dpot_dac_match,
256 },
257 };
258 module_platform_driver(dpot_dac_driver);
259
260 MODULE_DESCRIPTION("DAC emulation driver using a digital potentiometer");
261 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
262 MODULE_LICENSE("GPL v2");
263
