drivers/iio/adc/hx711.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * HX711: analog to digital converter for weight sensor module
   4  *
   5  * Copyright (c) 2016 Andreas Klinger <ak@it-klinger.de>
   6  */
   7 #include <linux/err.h>
   8 #include <linux/kernel.h>
   9 #include <linux/module.h>
  10 #include <linux/of.h>
  11 #include <linux/platform_device.h>
  12 #include <linux/property.h>
  13 #include <linux/slab.h>
  14 #include <linux/sched.h>
  15 #include <linux/delay.h>
  16 #include <linux/iio/iio.h>
  17 #include <linux/iio/sysfs.h>
  18 #include <linux/iio/buffer.h>
  19 #include <linux/iio/trigger_consumer.h>
  20 #include <linux/iio/triggered_buffer.h>
  21 #include <linux/gpio/consumer.h>
  22 #include <linux/regulator/consumer.h>
  23
  24 /* gain to pulse and scale conversion */
  25 #define HX711_GAIN_MAX          3
  26
  27 struct hx711_gain_to_scale {
  28         int                     gain;
  29         int                     gain_pulse;
  30         int                     scale;
  31         int                     channel;
  32 };
  33
  34 /*
  35  * .scale depends on AVDD which in turn is known as soon as the regulator
  36  * is available
  37  * therefore we set .scale in hx711_probe()
  38  *
  39  * channel A in documentation is channel 0 in source code
  40  * channel B in documentation is channel 1 in source code
  41  */
  42 static struct hx711_gain_to_scale hx711_gain_to_scale[HX711_GAIN_MAX] = {
  43         { 128, 1, 0, 0 },
  44         {  32, 2, 0, 1 },
  45         {  64, 3, 0, 0 }
  46 };
  47
  48 static int hx711_get_gain_to_pulse(int gain)
  49 {
  50         int i;
  51
  52         for (i = 0; i < HX711_GAIN_MAX; i++)
  53                 if (hx711_gain_to_scale[i].gain == gain)
  54                         return hx711_gain_to_scale[i].gain_pulse;
  55         return 1;
  56 }
  57
  58 static int hx711_get_gain_to_scale(int gain)
  59 {
  60         int i;
  61
  62         for (i = 0; i < HX711_GAIN_MAX; i++)
  63                 if (hx711_gain_to_scale[i].gain == gain)
  64                         return hx711_gain_to_scale[i].scale;
  65         return 0;
  66 }
  67
  68 static int hx711_get_scale_to_gain(int scale)
  69 {
  70         int i;
  71
  72         for (i = 0; i < HX711_GAIN_MAX; i++)
  73                 if (hx711_gain_to_scale[i].scale == scale)
  74                         return hx711_gain_to_scale[i].gain;
  75         return -EINVAL;
  76 }
  77
  78 struct hx711_data {
  79         struct device           *dev;
  80         struct gpio_desc        *gpiod_pd_sck;
  81         struct gpio_desc        *gpiod_dout;
  82         struct regulator        *reg_avdd;
  83         int                     gain_set;       /* gain set on device */
  84         int                     gain_chan_a;    /* gain for channel A */
  85         struct mutex            lock;
  86         /*
  87          * triggered buffer
  88          * 2x32-bit channel + 64-bit timestamp
  89          */
  90         u32                     buffer[4];
  91         /*
  92          * delay after a rising edge on SCK until the data is ready DOUT
  93          * this is dependent on the hx711 where the datasheet tells a
  94          * maximum value of 100 ns
  95          * but also on potential parasitic capacities on the wiring
  96          */
  97         u32                     data_ready_delay_ns;
  98         u32                     clock_frequency;
  99 };
 100
 101 static int hx711_cycle(struct hx711_data *hx711_data)
 102 {
 103         int val;
 104
 105         /*
 106          * if preempted for more then 60us while PD_SCK is high:
 107          * hx711 is going in reset
 108          * ==> measuring is false
 109          */
 110         preempt_disable();
 111         gpiod_set_value(hx711_data->gpiod_pd_sck, 1);
 112
 113         /*
 114          * wait until DOUT is ready
 115          * it turned out that parasitic capacities are extending the time
 116          * until DOUT has reached it's value
 117          */
 118         ndelay(hx711_data->data_ready_delay_ns);
 119
 120         val = gpiod_get_value(hx711_data->gpiod_dout);
 121         /*
 122          * here we are not waiting for 0.2 us as suggested by the datasheet,
 123          * because the oscilloscope showed in a test scenario
 124          * at least 1.15 us for PD_SCK high (T3 in datasheet)
 125          * and 0.56 us for PD_SCK low on TI Sitara with 800 MHz
 126          */
 127         gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
 128         preempt_enable();
 129
 130         /*
 131          * make it a square wave for addressing cases with capacitance on
 132          * PC_SCK
 133          */
 134         ndelay(hx711_data->data_ready_delay_ns);
 135
 136         return val;
 137 }
 138
 139 static int hx711_read(struct hx711_data *hx711_data)
 140 {
 141         int i, ret;
 142         int value = 0;
 143         int val = gpiod_get_value(hx711_data->gpiod_dout);
 144
 145         /* we double check if it's really down */
 146         if (val)
 147                 return -EIO;
 148
 149         for (i = 0; i < 24; i++) {
 150                 value <<= 1;
 151                 ret = hx711_cycle(hx711_data);
 152                 if (ret)
 153                         value++;
 154         }
 155
 156         value ^= 0x800000;
 157
 158         for (i = 0; i < hx711_get_gain_to_pulse(hx711_data->gain_set); i++)
 159                 hx711_cycle(hx711_data);
 160
 161         return value;
 162 }
 163
 164 static int hx711_wait_for_ready(struct hx711_data *hx711_data)
 165 {
 166         int i, val;
 167
 168         /*
 169          * in some rare cases the reset takes quite a long time
 170          * especially when the channel is changed.
 171          * Allow up to one second for it
 172          */
 173         for (i = 0; i < 100; i++) {
 174                 val = gpiod_get_value(hx711_data->gpiod_dout);
 175                 if (!val)
 176                         break;
 177                 /* sleep at least 10 ms */
 178                 msleep(10);
 179         }
 180         if (val)
 181                 return -EIO;
 182
 183         return 0;
 184 }
 185
 186 static int hx711_reset(struct hx711_data *hx711_data)
 187 {
 188         int ret;
 189         int val = gpiod_get_value(hx711_data->gpiod_dout);
 190
 191         if (val) {
 192                 /*
 193                  * an examination with the oszilloscope indicated
 194                  * that the first value read after the reset is not stable
 195                  * if we reset too short;
 196                  * the shorter the reset cycle
 197                  * the less reliable the first value after reset is;
 198                  * there were no problems encountered with a value
 199                  * of 10 ms or higher
 200                  */
 201                 gpiod_set_value(hx711_data->gpiod_pd_sck, 1);
 202                 msleep(10);
 203                 gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
 204
 205                 ret = hx711_wait_for_ready(hx711_data);
 206                 if (ret)
 207                         return ret;
 208                 /*
 209                  * after a reset the gain is 128 so we do a dummy read
 210                  * to set the gain for the next read
 211                  */
 212                 ret = hx711_read(hx711_data);
 213                 if (ret < 0)
 214                         return ret;
 215
 216                 /*
 217                  * after a dummy read we need to wait vor readiness
 218                  * for not mixing gain pulses with the clock
 219                  */
 220                 val = hx711_wait_for_ready(hx711_data);
 221         }
 222
 223         return val;
 224 }
 225
 226 static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)
 227 {
 228         int ret;
 229
 230         if (chan == 0) {
 231                 if (hx711_data->gain_set == 32) {
 232                         hx711_data->gain_set = hx711_data->gain_chan_a;
 233
 234                         ret = hx711_read(hx711_data);
 235                         if (ret < 0)
 236                                 return ret;
 237
 238                         ret = hx711_wait_for_ready(hx711_data);
 239                         if (ret)
 240                                 return ret;
 241                 }
 242         } else {
 243                 if (hx711_data->gain_set != 32) {
 244                         hx711_data->gain_set = 32;
 245
 246                         ret = hx711_read(hx711_data);
 247                         if (ret < 0)
 248                                 return ret;
 249
 250                         ret = hx711_wait_for_ready(hx711_data);
 251                         if (ret)
 252                                 return ret;
 253                 }
 254         }
 255
 256         return 0;
 257 }
 258
 259 static int hx711_reset_read(struct hx711_data *hx711_data, int chan)
 260 {
 261         int ret;
 262         int val;
 263
 264         /*
 265          * hx711_reset() must be called from here
 266          * because it could be calling hx711_read() by itself
 267          */
 268         if (hx711_reset(hx711_data)) {
 269                 dev_err(hx711_data->dev, "reset failed!");
 270                 return -EIO;
 271         }
 272
 273         ret = hx711_set_gain_for_channel(hx711_data, chan);
 274         if (ret < 0)
 275                 return ret;
 276
 277         val = hx711_read(hx711_data);
 278
 279         return val;
 280 }
 281
 282 static int hx711_read_raw(struct iio_dev *indio_dev,
 283                                 const struct iio_chan_spec *chan,
 284                                 int *val, int *val2, long mask)
 285 {
 286         struct hx711_data *hx711_data = iio_priv(indio_dev);
 287
 288         switch (mask) {
 289         case IIO_CHAN_INFO_RAW:
 290                 mutex_lock(&hx711_data->lock);
 291
 292                 *val = hx711_reset_read(hx711_data, chan->channel);
 293
 294                 mutex_unlock(&hx711_data->lock);
 295
 296                 if (*val < 0)
 297                         return *val;
 298                 return IIO_VAL_INT;
 299         case IIO_CHAN_INFO_SCALE:
 300                 *val = 0;
 301                 mutex_lock(&hx711_data->lock);
 302
 303                 *val2 = hx711_get_gain_to_scale(hx711_data->gain_set);
 304
 305                 mutex_unlock(&hx711_data->lock);
 306
 307                 return IIO_VAL_INT_PLUS_NANO;
 308         default:
 309                 return -EINVAL;
 310         }
 311 }
 312
 313 static int hx711_write_raw(struct iio_dev *indio_dev,
 314                                 struct iio_chan_spec const *chan,
 315                                 int val,
 316                                 int val2,
 317                                 long mask)
 318 {
 319         struct hx711_data *hx711_data = iio_priv(indio_dev);
 320         int ret;
 321         int gain;
 322
 323         switch (mask) {
 324         case IIO_CHAN_INFO_SCALE:
 325                 /*
 326                  * a scale greater than 1 mV per LSB is not possible
 327                  * with the HX711, therefore val must be 0
 328                  */
 329                 if (val != 0)
 330                         return -EINVAL;
 331
 332                 mutex_lock(&hx711_data->lock);
 333
 334                 gain = hx711_get_scale_to_gain(val2);
 335                 if (gain < 0) {
 336                         mutex_unlock(&hx711_data->lock);
 337                         return gain;
 338                 }
 339
 340                 if (gain != hx711_data->gain_set) {
 341                         hx711_data->gain_set = gain;
 342                         if (gain != 32)
 343                                 hx711_data->gain_chan_a = gain;
 344
 345                         ret = hx711_read(hx711_data);
 346                         if (ret < 0) {
 347                                 mutex_unlock(&hx711_data->lock);
 348                                 return ret;
 349                         }
 350                 }
 351
 352                 mutex_unlock(&hx711_data->lock);
 353                 return 0;
 354         default:
 355                 return -EINVAL;
 356         }
 357
 358         return 0;
 359 }
 360
 361 static int hx711_write_raw_get_fmt(struct iio_dev *indio_dev,
 362                 struct iio_chan_spec const *chan,
 363                 long mask)
 364 {
 365         return IIO_VAL_INT_PLUS_NANO;
 366 }
 367
 368 static irqreturn_t hx711_trigger(int irq, void *p)
 369 {
 370         struct iio_poll_func *pf = p;
 371         struct iio_dev *indio_dev = pf->indio_dev;
 372         struct hx711_data *hx711_data = iio_priv(indio_dev);
 373         int i, j = 0;
 374
 375         mutex_lock(&hx711_data->lock);
 376
 377         memset(hx711_data->buffer, 0, sizeof(hx711_data->buffer));
 378
 379         for (i = 0; i < indio_dev->masklength; i++) {
 380                 if (!test_bit(i, indio_dev->active_scan_mask))
 381                         continue;
 382
 383                 hx711_data->buffer[j] = hx711_reset_read(hx711_data,
 384                                         indio_dev->channels[i].channel);
 385                 j++;
 386         }
 387
 388         iio_push_to_buffers_with_timestamp(indio_dev, hx711_data->buffer,
 389                                                         pf->timestamp);
 390
 391         mutex_unlock(&hx711_data->lock);
 392
 393         iio_trigger_notify_done(indio_dev->trig);
 394
 395         return IRQ_HANDLED;
 396 }
 397
 398 static ssize_t hx711_scale_available_show(struct device *dev,
 399                                 struct device_attribute *attr,
 400                                 char *buf)
 401 {
 402         struct iio_dev_attr *iio_attr = to_iio_dev_attr(attr);
 403         int channel = iio_attr->address;
 404         int i, len = 0;
 405
 406         for (i = 0; i < HX711_GAIN_MAX; i++)
 407                 if (hx711_gain_to_scale[i].channel == channel)
 408                         len += sprintf(buf + len, "0.%09d ",
 409                                         hx711_gain_to_scale[i].scale);
 410
 411         len += sprintf(buf + len, "\n");
 412
 413         return len;
 414 }
 415
 416 static IIO_DEVICE_ATTR(in_voltage0_scale_available, S_IRUGO,
 417         hx711_scale_available_show, NULL, 0);
 418
 419 static IIO_DEVICE_ATTR(in_voltage1_scale_available, S_IRUGO,
 420         hx711_scale_available_show, NULL, 1);
 421
 422 static struct attribute *hx711_attributes[] = {
 423         &iio_dev_attr_in_voltage0_scale_available.dev_attr.attr,
 424         &iio_dev_attr_in_voltage1_scale_available.dev_attr.attr,
 425         NULL,
 426 };
 427
 428 static const struct attribute_group hx711_attribute_group = {
 429         .attrs = hx711_attributes,
 430 };
 431
 432 static const struct iio_info hx711_iio_info = {
 433         .read_raw               = hx711_read_raw,
 434         .write_raw              = hx711_write_raw,
 435         .write_raw_get_fmt      = hx711_write_raw_get_fmt,
 436         .attrs                  = &hx711_attribute_group,
 437 };
 438
 439 static const struct iio_chan_spec hx711_chan_spec[] = {
 440         {
 441                 .type = IIO_VOLTAGE,
 442                 .channel = 0,
 443                 .indexed = 1,
 444                 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
 445                 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
 446                 .scan_index = 0,
 447                 .scan_type = {
 448                         .sign = 'u',
 449                         .realbits = 24,
 450                         .storagebits = 32,
 451                         .endianness = IIO_CPU,
 452                 },
 453         },
 454         {
 455                 .type = IIO_VOLTAGE,
 456                 .channel = 1,
 457                 .indexed = 1,
 458                 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
 459                 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
 460                 .scan_index = 1,
 461                 .scan_type = {
 462                         .sign = 'u',
 463                         .realbits = 24,
 464                         .storagebits = 32,
 465                         .endianness = IIO_CPU,
 466                 },
 467         },
 468         IIO_CHAN_SOFT_TIMESTAMP(2),
 469 };
 470
 471 static int hx711_probe(struct platform_device *pdev)
 472 {
 473         struct device *dev = &pdev->dev;
 474         struct device_node *np = dev->of_node;
 475         struct hx711_data *hx711_data;
 476         struct iio_dev *indio_dev;
 477         int ret;
 478         int i;
 479
 480         indio_dev = devm_iio_device_alloc(dev, sizeof(struct hx711_data));
 481         if (!indio_dev) {
 482                 dev_err(dev, "failed to allocate IIO device\n");
 483                 return -ENOMEM;
 484         }
 485
 486         hx711_data = iio_priv(indio_dev);
 487         hx711_data->dev = dev;
 488
 489         mutex_init(&hx711_data->lock);
 490
 491         /*
 492          * PD_SCK stands for power down and serial clock input of HX711
 493          * in the driver it is an output
 494          */
 495         hx711_data->gpiod_pd_sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
 496         if (IS_ERR(hx711_data->gpiod_pd_sck)) {
 497                 dev_err(dev, "failed to get sck-gpiod: err=%ld\n",
 498                                         PTR_ERR(hx711_data->gpiod_pd_sck));
 499                 return PTR_ERR(hx711_data->gpiod_pd_sck);
 500         }
 501
 502         /*
 503          * DOUT stands for serial data output of HX711
 504          * for the driver it is an input
 505          */
 506         hx711_data->gpiod_dout = devm_gpiod_get(dev, "dout", GPIOD_IN);
 507         if (IS_ERR(hx711_data->gpiod_dout)) {
 508                 dev_err(dev, "failed to get dout-gpiod: err=%ld\n",
 509                                         PTR_ERR(hx711_data->gpiod_dout));
 510                 return PTR_ERR(hx711_data->gpiod_dout);
 511         }
 512
 513         hx711_data->reg_avdd = devm_regulator_get(dev, "avdd");
 514         if (IS_ERR(hx711_data->reg_avdd))
 515                 return PTR_ERR(hx711_data->reg_avdd);
 516
 517         ret = regulator_enable(hx711_data->reg_avdd);
 518         if (ret < 0)
 519                 return ret;
 520
 521         /*
 522          * with
 523          * full scale differential input range: AVDD / GAIN
 524          * full scale output data: 2^24
 525          * we can say:
 526          *     AVDD / GAIN = 2^24
 527          * therefore:
 528          *     1 LSB = AVDD / GAIN / 2^24
 529          * AVDD is in uV, but we need 10^-9 mV
 530          * approximately to fit into a 32 bit number:
 531          * 1 LSB = (AVDD * 100) / GAIN / 1678 [10^-9 mV]
 532          */
 533         ret = regulator_get_voltage(hx711_data->reg_avdd);
 534         if (ret < 0)
 535                 goto error_regulator;
 536
 537         /* we need 10^-9 mV */
 538         ret *= 100;
 539
 540         for (i = 0; i < HX711_GAIN_MAX; i++)
 541                 hx711_gain_to_scale[i].scale =
 542                         ret / hx711_gain_to_scale[i].gain / 1678;
 543
 544         hx711_data->gain_set = 128;
 545         hx711_data->gain_chan_a = 128;
 546
 547         hx711_data->clock_frequency = 400000;
 548         ret = of_property_read_u32(np, "clock-frequency",
 549                                         &hx711_data->clock_frequency);
 550
 551         /*
 552          * datasheet says the high level of PD_SCK has a maximum duration
 553          * of 50 microseconds
 554          */
 555         if (hx711_data->clock_frequency < 20000) {
 556                 dev_warn(dev, "clock-frequency too low - assuming 400 kHz\n");
 557                 hx711_data->clock_frequency = 400000;
 558         }
 559
 560         hx711_data->data_ready_delay_ns =
 561                                 1000000000 / hx711_data->clock_frequency;
 562
 563         platform_set_drvdata(pdev, indio_dev);
 564
 565         indio_dev->name = "hx711";
 566         indio_dev->dev.parent = &pdev->dev;
 567         indio_dev->info = &hx711_iio_info;
 568         indio_dev->modes = INDIO_DIRECT_MODE;
 569         indio_dev->channels = hx711_chan_spec;
 570         indio_dev->num_channels = ARRAY_SIZE(hx711_chan_spec);
 571
 572         ret = iio_triggered_buffer_setup(indio_dev, iio_pollfunc_store_time,
 573                                                         hx711_trigger, NULL);
 574         if (ret < 0) {
 575                 dev_err(dev, "setup of iio triggered buffer failed\n");
 576                 goto error_regulator;
 577         }
 578
 579         ret = iio_device_register(indio_dev);
 580         if (ret < 0) {
 581                 dev_err(dev, "Couldn't register the device\n");
 582                 goto error_buffer;
 583         }
 584
 585         return 0;
 586
 587 error_buffer:
 588         iio_triggered_buffer_cleanup(indio_dev);
 589
 590 error_regulator:
 591         regulator_disable(hx711_data->reg_avdd);
 592
 593         return ret;
 594 }
 595
 596 static int hx711_remove(struct platform_device *pdev)
 597 {
 598         struct hx711_data *hx711_data;
 599         struct iio_dev *indio_dev;
 600
 601         indio_dev = platform_get_drvdata(pdev);
 602         hx711_data = iio_priv(indio_dev);
 603
 604         iio_device_unregister(indio_dev);
 605
 606         iio_triggered_buffer_cleanup(indio_dev);
 607
 608         regulator_disable(hx711_data->reg_avdd);
 609
 610         return 0;
 611 }
 612
 613 static const struct of_device_id of_hx711_match[] = {
 614         { .compatible = "avia,hx711", },
 615         {},
 616 };
 617
 618 MODULE_DEVICE_TABLE(of, of_hx711_match);
 619
 620 static struct platform_driver hx711_driver = {
 621         .probe          = hx711_probe,
 622         .remove         = hx711_remove,
 623         .driver         = {
 624                 .name           = "hx711-gpio",
 625                 .of_match_table = of_hx711_match,
 626         },
 627 };
 628
 629 module_platform_driver(hx711_driver);
 630
 631 MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
 632 MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
 633 MODULE_LICENSE("GPL");
 634 MODULE_ALIAS("platform:hx711-gpio");
 635