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/mod_devicetable.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 #define HX711_RESET_GAIN 128 27 28 struct hx711_gain_to_scale { 29 int gain; 30 int gain_pulse; 31 int scale; 32 int channel; 33 }; 34 35 /* 36 * .scale depends on AVDD which in turn is known as soon as the regulator 37 * is available 38 * therefore we set .scale in hx711_probe() 39 * 40 * channel A in documentation is channel 0 in source code 41 * channel B in documentation is channel 1 in source code 42 */ 43 static struct hx711_gain_to_scale hx711_gain_to_scale[HX711_GAIN_MAX] = { 44 { 128, 1, 0, 0 }, 45 { 32, 2, 0, 1 }, 46 { 64, 3, 0, 0 } 47 }; 48 49 static int hx711_get_gain_to_pulse(int gain) 50 { 51 int i; 52 53 for (i = 0; i < HX711_GAIN_MAX; i++) 54 if (hx711_gain_to_scale[i].gain == gain) 55 return hx711_gain_to_scale[i].gain_pulse; 56 return 1; 57 } 58 59 static int hx711_get_gain_to_scale(int gain) 60 { 61 int i; 62 63 for (i = 0; i < HX711_GAIN_MAX; i++) 64 if (hx711_gain_to_scale[i].gain == gain) 65 return hx711_gain_to_scale[i].scale; 66 return 0; 67 } 68 69 static int hx711_get_scale_to_gain(int scale) 70 { 71 int i; 72 73 for (i = 0; i < HX711_GAIN_MAX; i++) 74 if (hx711_gain_to_scale[i].scale == scale) 75 return hx711_gain_to_scale[i].gain; 76 return -EINVAL; 77 } 78 79 struct hx711_data { 80 struct device *dev; 81 struct gpio_desc *gpiod_pd_sck; 82 struct gpio_desc *gpiod_dout; 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 naturally aligned timestamp 89 */ 90 struct { 91 u32 channel[2]; 92 aligned_s64 timestamp; 93 } buffer; 94 /* 95 * delay after a rising edge on SCK until the data is ready DOUT 96 * this is dependent on the hx711 where the datasheet tells a 97 * maximum value of 100 ns 98 * but also on potential parasitic capacities on the wiring 99 */ 100 u32 data_ready_delay_ns; 101 u32 clock_frequency; 102 }; 103 104 static int hx711_cycle(struct hx711_data *hx711_data) 105 { 106 unsigned long flags; 107 108 /* 109 * if preempted for more then 60us while PD_SCK is high: 110 * hx711 is going in reset 111 * ==> measuring is false 112 */ 113 local_irq_save(flags); 114 gpiod_set_value(hx711_data->gpiod_pd_sck, 1); 115 116 /* 117 * wait until DOUT is ready 118 * it turned out that parasitic capacities are extending the time 119 * until DOUT has reached it's value 120 */ 121 ndelay(hx711_data->data_ready_delay_ns); 122 123 /* 124 * here we are not waiting for 0.2 us as suggested by the datasheet, 125 * because the oscilloscope showed in a test scenario 126 * at least 1.15 us for PD_SCK high (T3 in datasheet) 127 * and 0.56 us for PD_SCK low on TI Sitara with 800 MHz 128 */ 129 gpiod_set_value(hx711_data->gpiod_pd_sck, 0); 130 local_irq_restore(flags); 131 132 /* 133 * make it a square wave for addressing cases with capacitance on 134 * PC_SCK 135 */ 136 ndelay(hx711_data->data_ready_delay_ns); 137 138 /* sample as late as possible */ 139 return gpiod_get_value(hx711_data->gpiod_dout); 140 } 141 142 static int hx711_read(struct hx711_data *hx711_data) 143 { 144 int i, ret; 145 int value = 0; 146 int val = gpiod_get_value(hx711_data->gpiod_dout); 147 148 /* we double check if it's really down */ 149 if (val) 150 return -EIO; 151 152 for (i = 0; i < 24; i++) { 153 value <<= 1; 154 ret = hx711_cycle(hx711_data); 155 if (ret) 156 value++; 157 } 158 159 value ^= 0x800000; 160 161 for (i = 0; i < hx711_get_gain_to_pulse(hx711_data->gain_set); i++) 162 hx711_cycle(hx711_data); 163 164 return value; 165 } 166 167 static int hx711_wait_for_ready(struct hx711_data *hx711_data) 168 { 169 int i, val; 170 171 /* 172 * in some rare cases the reset takes quite a long time 173 * especially when the channel is changed. 174 * Allow up to one second for it 175 */ 176 for (i = 0; i < 100; i++) { 177 val = gpiod_get_value(hx711_data->gpiod_dout); 178 if (!val) 179 break; 180 /* sleep at least 10 ms */ 181 msleep(10); 182 } 183 if (val) 184 return -EIO; 185 186 return 0; 187 } 188 189 static int hx711_reset(struct hx711_data *hx711_data) 190 { 191 int val = hx711_wait_for_ready(hx711_data); 192 193 if (val) { 194 /* 195 * an examination with the oszilloscope indicated 196 * that the first value read after the reset is not stable 197 * if we reset too short; 198 * the shorter the reset cycle 199 * the less reliable the first value after reset is; 200 * there were no problems encountered with a value 201 * of 10 ms or higher 202 */ 203 gpiod_set_value(hx711_data->gpiod_pd_sck, 1); 204 msleep(10); 205 gpiod_set_value(hx711_data->gpiod_pd_sck, 0); 206 207 val = hx711_wait_for_ready(hx711_data); 208 209 /* after a reset the gain is 128 */ 210 hx711_data->gain_set = HX711_RESET_GAIN; 211 } 212 213 return val; 214 } 215 216 static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan) 217 { 218 int ret; 219 220 if (chan == 0) { 221 if (hx711_data->gain_set == 32) { 222 hx711_data->gain_set = hx711_data->gain_chan_a; 223 224 ret = hx711_read(hx711_data); 225 if (ret < 0) 226 return ret; 227 228 ret = hx711_wait_for_ready(hx711_data); 229 if (ret) 230 return ret; 231 } 232 } else { 233 if (hx711_data->gain_set != 32) { 234 hx711_data->gain_set = 32; 235 236 ret = hx711_read(hx711_data); 237 if (ret < 0) 238 return ret; 239 240 ret = hx711_wait_for_ready(hx711_data); 241 if (ret) 242 return ret; 243 } 244 } 245 246 return 0; 247 } 248 249 static int hx711_reset_read(struct hx711_data *hx711_data, int chan) 250 { 251 int ret; 252 int val; 253 254 /* 255 * hx711_reset() must be called from here 256 * because it could be calling hx711_read() by itself 257 */ 258 if (hx711_reset(hx711_data)) { 259 dev_err(hx711_data->dev, "reset failed!"); 260 return -EIO; 261 } 262 263 ret = hx711_set_gain_for_channel(hx711_data, chan); 264 if (ret < 0) 265 return ret; 266 267 val = hx711_read(hx711_data); 268 269 return val; 270 } 271 272 static int hx711_read_raw(struct iio_dev *indio_dev, 273 const struct iio_chan_spec *chan, 274 int *val, int *val2, long mask) 275 { 276 struct hx711_data *hx711_data = iio_priv(indio_dev); 277 278 switch (mask) { 279 case IIO_CHAN_INFO_RAW: 280 mutex_lock(&hx711_data->lock); 281 282 *val = hx711_reset_read(hx711_data, chan->channel); 283 284 mutex_unlock(&hx711_data->lock); 285 286 if (*val < 0) 287 return *val; 288 return IIO_VAL_INT; 289 case IIO_CHAN_INFO_SCALE: 290 *val = 0; 291 mutex_lock(&hx711_data->lock); 292 293 *val2 = hx711_get_gain_to_scale(hx711_data->gain_set); 294 295 mutex_unlock(&hx711_data->lock); 296 297 return IIO_VAL_INT_PLUS_NANO; 298 default: 299 return -EINVAL; 300 } 301 } 302 303 static int hx711_write_raw(struct iio_dev *indio_dev, 304 struct iio_chan_spec const *chan, 305 int val, 306 int val2, 307 long mask) 308 { 309 struct hx711_data *hx711_data = iio_priv(indio_dev); 310 int ret; 311 int gain; 312 313 switch (mask) { 314 case IIO_CHAN_INFO_SCALE: 315 /* 316 * a scale greater than 1 mV per LSB is not possible 317 * with the HX711, therefore val must be 0 318 */ 319 if (val != 0) 320 return -EINVAL; 321 322 mutex_lock(&hx711_data->lock); 323 324 gain = hx711_get_scale_to_gain(val2); 325 if (gain < 0) { 326 mutex_unlock(&hx711_data->lock); 327 return gain; 328 } 329 330 if (gain != hx711_data->gain_set) { 331 hx711_data->gain_set = gain; 332 if (gain != 32) 333 hx711_data->gain_chan_a = gain; 334 335 ret = hx711_read(hx711_data); 336 if (ret < 0) { 337 mutex_unlock(&hx711_data->lock); 338 return ret; 339 } 340 } 341 342 mutex_unlock(&hx711_data->lock); 343 return 0; 344 default: 345 return -EINVAL; 346 } 347 348 return 0; 349 } 350 351 static int hx711_write_raw_get_fmt(struct iio_dev *indio_dev, 352 struct iio_chan_spec const *chan, 353 long mask) 354 { 355 return IIO_VAL_INT_PLUS_NANO; 356 } 357 358 static irqreturn_t hx711_trigger(int irq, void *p) 359 { 360 struct iio_poll_func *pf = p; 361 struct iio_dev *indio_dev = pf->indio_dev; 362 struct hx711_data *hx711_data = iio_priv(indio_dev); 363 int i, j = 0; 364 365 mutex_lock(&hx711_data->lock); 366 367 memset(&hx711_data->buffer, 0, sizeof(hx711_data->buffer)); 368 369 iio_for_each_active_channel(indio_dev, i) { 370 hx711_data->buffer.channel[j] = hx711_reset_read(hx711_data, 371 indio_dev->channels[i].channel); 372 j++; 373 } 374 375 iio_push_to_buffers_with_timestamp(indio_dev, &hx711_data->buffer, 376 pf->timestamp); 377 378 mutex_unlock(&hx711_data->lock); 379 380 iio_trigger_notify_done(indio_dev->trig); 381 382 return IRQ_HANDLED; 383 } 384 385 static ssize_t hx711_scale_available_show(struct device *dev, 386 struct device_attribute *attr, 387 char *buf) 388 { 389 struct iio_dev_attr *iio_attr = to_iio_dev_attr(attr); 390 int channel = iio_attr->address; 391 int i, len = 0; 392 393 for (i = 0; i < HX711_GAIN_MAX; i++) 394 if (hx711_gain_to_scale[i].channel == channel) 395 len += sprintf(buf + len, "0.%09d ", 396 hx711_gain_to_scale[i].scale); 397 398 len += sprintf(buf + len, "\n"); 399 400 return len; 401 } 402 403 static IIO_DEVICE_ATTR(in_voltage0_scale_available, S_IRUGO, 404 hx711_scale_available_show, NULL, 0); 405 406 static IIO_DEVICE_ATTR(in_voltage1_scale_available, S_IRUGO, 407 hx711_scale_available_show, NULL, 1); 408 409 static struct attribute *hx711_attributes[] = { 410 &iio_dev_attr_in_voltage0_scale_available.dev_attr.attr, 411 &iio_dev_attr_in_voltage1_scale_available.dev_attr.attr, 412 NULL, 413 }; 414 415 static const struct attribute_group hx711_attribute_group = { 416 .attrs = hx711_attributes, 417 }; 418 419 static const struct iio_info hx711_iio_info = { 420 .read_raw = hx711_read_raw, 421 .write_raw = hx711_write_raw, 422 .write_raw_get_fmt = hx711_write_raw_get_fmt, 423 .attrs = &hx711_attribute_group, 424 }; 425 426 static const struct iio_chan_spec hx711_chan_spec[] = { 427 { 428 .type = IIO_VOLTAGE, 429 .channel = 0, 430 .indexed = 1, 431 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), 432 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), 433 .scan_index = 0, 434 .scan_type = { 435 .sign = 'u', 436 .realbits = 24, 437 .storagebits = 32, 438 .endianness = IIO_CPU, 439 }, 440 }, 441 { 442 .type = IIO_VOLTAGE, 443 .channel = 1, 444 .indexed = 1, 445 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), 446 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), 447 .scan_index = 1, 448 .scan_type = { 449 .sign = 'u', 450 .realbits = 24, 451 .storagebits = 32, 452 .endianness = IIO_CPU, 453 }, 454 }, 455 IIO_CHAN_SOFT_TIMESTAMP(2), 456 }; 457 458 static int hx711_probe(struct platform_device *pdev) 459 { 460 struct device *dev = &pdev->dev; 461 struct hx711_data *hx711_data; 462 struct iio_dev *indio_dev; 463 int ret; 464 int i; 465 466 indio_dev = devm_iio_device_alloc(dev, sizeof(struct hx711_data)); 467 if (!indio_dev) 468 return dev_err_probe(dev, -ENOMEM, "failed to allocate IIO device\n"); 469 470 hx711_data = iio_priv(indio_dev); 471 hx711_data->dev = dev; 472 473 mutex_init(&hx711_data->lock); 474 475 /* 476 * PD_SCK stands for power down and serial clock input of HX711 477 * in the driver it is an output 478 */ 479 hx711_data->gpiod_pd_sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW); 480 if (IS_ERR(hx711_data->gpiod_pd_sck)) 481 return dev_err_probe(dev, PTR_ERR(hx711_data->gpiod_pd_sck), 482 "failed to get sck-gpiod\n"); 483 484 /* 485 * DOUT stands for serial data output of HX711 486 * for the driver it is an input 487 */ 488 hx711_data->gpiod_dout = devm_gpiod_get(dev, "dout", GPIOD_IN); 489 if (IS_ERR(hx711_data->gpiod_dout)) 490 return dev_err_probe(dev, PTR_ERR(hx711_data->gpiod_dout), 491 "failed to get dout-gpiod\n"); 492 493 ret = devm_regulator_get_enable_read_voltage(dev, "avdd"); 494 if (ret < 0) 495 return ret; 496 497 /* 498 * with 499 * full scale differential input range: AVDD / GAIN 500 * full scale output data: 2^24 501 * we can say: 502 * AVDD / GAIN = 2^24 503 * therefore: 504 * 1 LSB = AVDD / GAIN / 2^24 505 * AVDD is in uV, but we need 10^-9 mV 506 * approximately to fit into a 32 bit number: 507 * 1 LSB = (AVDD * 100) / GAIN / 1678 [10^-9 mV] 508 */ 509 510 /* we need 10^-9 mV */ 511 ret *= 100; 512 513 for (i = 0; i < HX711_GAIN_MAX; i++) 514 hx711_gain_to_scale[i].scale = 515 ret / hx711_gain_to_scale[i].gain / 1678; 516 517 hx711_data->gain_set = 128; 518 hx711_data->gain_chan_a = 128; 519 520 hx711_data->clock_frequency = 400000; 521 ret = device_property_read_u32(&pdev->dev, "clock-frequency", 522 &hx711_data->clock_frequency); 523 524 /* 525 * datasheet says the high level of PD_SCK has a maximum duration 526 * of 50 microseconds 527 */ 528 if (hx711_data->clock_frequency < 20000) { 529 dev_warn(dev, "clock-frequency too low - assuming 400 kHz\n"); 530 hx711_data->clock_frequency = 400000; 531 } 532 533 hx711_data->data_ready_delay_ns = 534 1000000000 / hx711_data->clock_frequency; 535 536 indio_dev->name = "hx711"; 537 indio_dev->info = &hx711_iio_info; 538 indio_dev->modes = INDIO_DIRECT_MODE; 539 indio_dev->channels = hx711_chan_spec; 540 indio_dev->num_channels = ARRAY_SIZE(hx711_chan_spec); 541 542 ret = devm_iio_triggered_buffer_setup(dev, indio_dev, 543 iio_pollfunc_store_time, 544 hx711_trigger, NULL); 545 if (ret < 0) 546 return dev_err_probe(dev, ret, 547 "setup of iio triggered buffer failed\n"); 548 549 ret = devm_iio_device_register(dev, indio_dev); 550 if (ret < 0) 551 return dev_err_probe(dev, ret, "Couldn't register the device\n"); 552 553 return 0; 554 } 555 556 static const struct of_device_id of_hx711_match[] = { 557 { .compatible = "avia,hx711", }, 558 { } 559 }; 560 561 MODULE_DEVICE_TABLE(of, of_hx711_match); 562 563 static struct platform_driver hx711_driver = { 564 .probe = hx711_probe, 565 .driver = { 566 .name = "hx711-gpio", 567 .of_match_table = of_hx711_match, 568 }, 569 }; 570 571 module_platform_driver(hx711_driver); 572 573 MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>"); 574 MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells"); 575 MODULE_LICENSE("GPL"); 576 MODULE_ALIAS("platform:hx711-gpio"); 577 578