drivers/video/backlight/pwm_bl.c

   1 /*
   2  * linux/drivers/video/backlight/pwm_bl.c
   3  *
   4  * simple PWM based backlight control, board code has to setup
   5  * 1) pin configuration so PWM waveforms can output
   6  * 2) platform_data being correctly configured
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 #include <linux/delay.h>
  14 #include <linux/gpio/consumer.h>
  15 #include <linux/gpio.h>
  16 #include <linux/module.h>
  17 #include <linux/kernel.h>
  18 #include <linux/init.h>
  19 #include <linux/platform_device.h>
  20 #include <linux/fb.h>
  21 #include <linux/backlight.h>
  22 #include <linux/err.h>
  23 #include <linux/pwm.h>
  24 #include <linux/pwm_backlight.h>
  25 #include <linux/regulator/consumer.h>
  26 #include <linux/slab.h>
  27
  28 struct pwm_bl_data {
  29         struct pwm_device       *pwm;
  30         struct device           *dev;
  31         unsigned int            period;
  32         unsigned int            lth_brightness;
  33         unsigned int            *levels;
  34         bool                    enabled;
  35         struct regulator        *power_supply;
  36         struct gpio_desc        *enable_gpio;
  37         unsigned int            scale;
  38         bool                    legacy;
  39         unsigned int            post_pwm_on_delay;
  40         unsigned int            pwm_off_delay;
  41         int                     (*notify)(struct device *,
  42                                           int brightness);
  43         void                    (*notify_after)(struct device *,
  44                                         int brightness);
  45         int                     (*check_fb)(struct device *, struct fb_info *);
  46         void                    (*exit)(struct device *);
  47 };
  48
  49 static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)
  50 {
  51         int err;
  52
  53         if (pb->enabled)
  54                 return;
  55
  56         err = regulator_enable(pb->power_supply);
  57         if (err < 0)
  58                 dev_err(pb->dev, "failed to enable power supply\n");
  59
  60         pwm_enable(pb->pwm);
  61
  62         if (pb->post_pwm_on_delay)
  63                 msleep(pb->post_pwm_on_delay);
  64
  65         if (pb->enable_gpio)
  66                 gpiod_set_value_cansleep(pb->enable_gpio, 1);
  67
  68         pb->enabled = true;
  69 }
  70
  71 static void pwm_backlight_power_off(struct pwm_bl_data *pb)
  72 {
  73         if (!pb->enabled)
  74                 return;
  75
  76         if (pb->enable_gpio)
  77                 gpiod_set_value_cansleep(pb->enable_gpio, 0);
  78
  79         if (pb->pwm_off_delay)
  80                 msleep(pb->pwm_off_delay);
  81
  82         pwm_config(pb->pwm, 0, pb->period);
  83         pwm_disable(pb->pwm);
  84
  85         regulator_disable(pb->power_supply);
  86         pb->enabled = false;
  87 }
  88
  89 static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
  90 {
  91         unsigned int lth = pb->lth_brightness;
  92         u64 duty_cycle;
  93
  94         if (pb->levels)
  95                 duty_cycle = pb->levels[brightness];
  96         else
  97                 duty_cycle = brightness;
  98
  99         duty_cycle *= pb->period - lth;
 100         do_div(duty_cycle, pb->scale);
 101
 102         return duty_cycle + lth;
 103 }
 104
 105 static int pwm_backlight_update_status(struct backlight_device *bl)
 106 {
 107         struct pwm_bl_data *pb = bl_get_data(bl);
 108         int brightness = bl->props.brightness;
 109         int duty_cycle;
 110
 111         if (bl->props.power != FB_BLANK_UNBLANK ||
 112             bl->props.fb_blank != FB_BLANK_UNBLANK ||
 113             bl->props.state & BL_CORE_FBBLANK)
 114                 brightness = 0;
 115
 116         if (pb->notify)
 117                 brightness = pb->notify(pb->dev, brightness);
 118
 119         if (brightness > 0) {
 120                 duty_cycle = compute_duty_cycle(pb, brightness);
 121                 pwm_config(pb->pwm, duty_cycle, pb->period);
 122                 pwm_backlight_power_on(pb, brightness);
 123         } else
 124                 pwm_backlight_power_off(pb);
 125
 126         if (pb->notify_after)
 127                 pb->notify_after(pb->dev, brightness);
 128
 129         return 0;
 130 }
 131
 132 static int pwm_backlight_check_fb(struct backlight_device *bl,
 133                                   struct fb_info *info)
 134 {
 135         struct pwm_bl_data *pb = bl_get_data(bl);
 136
 137         return !pb->check_fb || pb->check_fb(pb->dev, info);
 138 }
 139
 140 static const struct backlight_ops pwm_backlight_ops = {
 141         .update_status  = pwm_backlight_update_status,
 142         .check_fb       = pwm_backlight_check_fb,
 143 };
 144
 145 #ifdef CONFIG_OF
 146 #define PWM_LUMINANCE_SCALE     10000 /* luminance scale */
 147
 148 /* An integer based power function */
 149 static u64 int_pow(u64 base, int exp)
 150 {
 151         u64 result = 1;
 152
 153         while (exp) {
 154                 if (exp & 1)
 155                         result *= base;
 156                 exp >>= 1;
 157                 base *= base;
 158         }
 159
 160         return result;
 161 }
 162
 163 /*
 164  * CIE lightness to PWM conversion.
 165  *
 166  * The CIE 1931 lightness formula is what actually describes how we perceive
 167  * light:
 168  *          Y = (L* / 902.3)           if L* ≤ 0.08856
 169  *          Y = ((L* + 16) / 116)^3    if L* > 0.08856
 170  *
 171  * Where Y is the luminance, the amount of light coming out of the screen, and
 172  * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
 173  * perceives the screen to be, and is a number between 0 and 100.
 174  *
 175  * The following function does the fixed point maths needed to implement the
 176  * above formula.
 177  */
 178 static u64 cie1931(unsigned int lightness, unsigned int scale)
 179 {
 180         u64 retval;
 181
 182         lightness *= 100;
 183         if (lightness <= (8 * scale)) {
 184                 retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023);
 185         } else {
 186                 retval = int_pow((lightness + (16 * scale)) / 116, 3);
 187                 retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
 188         }
 189
 190         return retval;
 191 }
 192
 193 /*
 194  * Create a default correction table for PWM values to create linear brightness
 195  * for LED based backlights using the CIE1931 algorithm.
 196  */
 197 static
 198 int pwm_backlight_brightness_default(struct device *dev,
 199                                      struct platform_pwm_backlight_data *data,
 200                                      unsigned int period)
 201 {
 202         unsigned int i;
 203         u64 retval;
 204
 205         /*
 206          * Once we have 4096 levels there's little point going much higher...
 207          * neither interactive sliders nor animation benefits from having
 208          * more values in the table.
 209          */
 210         data->max_brightness =
 211                 min((int)DIV_ROUND_UP(period, fls(period)), 4096);
 212
 213         data->levels = devm_kcalloc(dev, data->max_brightness,
 214                                     sizeof(*data->levels), GFP_KERNEL);
 215         if (!data->levels)
 216                 return -ENOMEM;
 217
 218         /* Fill the table using the cie1931 algorithm */
 219         for (i = 0; i < data->max_brightness; i++) {
 220                 retval = cie1931((i * PWM_LUMINANCE_SCALE) /
 221                                  data->max_brightness, PWM_LUMINANCE_SCALE) *
 222                                  period;
 223                 retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
 224                 if (retval > UINT_MAX)
 225                         return -EINVAL;
 226                 data->levels[i] = (unsigned int)retval;
 227         }
 228
 229         data->dft_brightness = data->max_brightness / 2;
 230         data->max_brightness--;
 231
 232         return 0;
 233 }
 234
 235 static int pwm_backlight_parse_dt(struct device *dev,
 236                                   struct platform_pwm_backlight_data *data)
 237 {
 238         struct device_node *node = dev->of_node;
 239         unsigned int num_levels = 0;
 240         unsigned int levels_count;
 241         unsigned int num_steps = 0;
 242         struct property *prop;
 243         unsigned int *table;
 244         int length;
 245         u32 value;
 246         int ret;
 247
 248         if (!node)
 249                 return -ENODEV;
 250
 251         memset(data, 0, sizeof(*data));
 252
 253         /*
 254          * These values are optional and set as 0 by default, the out values
 255          * are modified only if a valid u32 value can be decoded.
 256          */
 257         of_property_read_u32(node, "post-pwm-on-delay-ms",
 258                              &data->post_pwm_on_delay);
 259         of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay);
 260
 261         data->enable_gpio = -EINVAL;
 262
 263         /*
 264          * Determine the number of brightness levels, if this property is not
 265          * set a default table of brightness levels will be used.
 266          */
 267         prop = of_find_property(node, "brightness-levels", &length);
 268         if (!prop)
 269                 return 0;
 270
 271         data->max_brightness = length / sizeof(u32);
 272
 273         /* read brightness levels from DT property */
 274         if (data->max_brightness > 0) {
 275                 size_t size = sizeof(*data->levels) * data->max_brightness;
 276                 unsigned int i, j, n = 0;
 277
 278                 data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
 279                 if (!data->levels)
 280                         return -ENOMEM;
 281
 282                 ret = of_property_read_u32_array(node, "brightness-levels",
 283                                                  data->levels,
 284                                                  data->max_brightness);
 285                 if (ret < 0)
 286                         return ret;
 287
 288                 ret = of_property_read_u32(node, "default-brightness-level",
 289                                            &value);
 290                 if (ret < 0)
 291                         return ret;
 292
 293                 data->dft_brightness = value;
 294
 295                 /*
 296                  * This property is optional, if is set enables linear
 297                  * interpolation between each of the values of brightness levels
 298                  * and creates a new pre-computed table.
 299                  */
 300                 of_property_read_u32(node, "num-interpolated-steps",
 301                                      &num_steps);
 302
 303                 /*
 304                  * Make sure that there is at least two entries in the
 305                  * brightness-levels table, otherwise we can't interpolate
 306                  * between two points.
 307                  */
 308                 if (num_steps) {
 309                         if (data->max_brightness < 2) {
 310                                 dev_err(dev, "can't interpolate\n");
 311                                 return -EINVAL;
 312                         }
 313
 314                         /*
 315                          * Recalculate the number of brightness levels, now
 316                          * taking in consideration the number of interpolated
 317                          * steps between two levels.
 318                          */
 319                         for (i = 0; i < data->max_brightness - 1; i++) {
 320                                 if ((data->levels[i + 1] - data->levels[i]) /
 321                                    num_steps)
 322                                         num_levels += num_steps;
 323                                 else
 324                                         num_levels++;
 325                         }
 326                         num_levels++;
 327                         dev_dbg(dev, "new number of brightness levels: %d\n",
 328                                 num_levels);
 329
 330                         /*
 331                          * Create a new table of brightness levels with all the
 332                          * interpolated steps.
 333                          */
 334                         size = sizeof(*table) * num_levels;
 335                         table = devm_kzalloc(dev, size, GFP_KERNEL);
 336                         if (!table)
 337                                 return -ENOMEM;
 338
 339                         /* Fill the interpolated table. */
 340                         levels_count = 0;
 341                         for (i = 0; i < data->max_brightness - 1; i++) {
 342                                 value = data->levels[i];
 343                                 n = (data->levels[i + 1] - value) / num_steps;
 344                                 if (n > 0) {
 345                                         for (j = 0; j < num_steps; j++) {
 346                                                 table[levels_count] = value;
 347                                                 value += n;
 348                                                 levels_count++;
 349                                         }
 350                                 } else {
 351                                         table[levels_count] = data->levels[i];
 352                                         levels_count++;
 353                                 }
 354                         }
 355                         table[levels_count] = data->levels[i];
 356
 357                         /*
 358                          * As we use interpolation lets remove current
 359                          * brightness levels table and replace for the
 360                          * new interpolated table.
 361                          */
 362                         devm_kfree(dev, data->levels);
 363                         data->levels = table;
 364
 365                         /*
 366                          * Reassign max_brightness value to the new total number
 367                          * of brightness levels.
 368                          */
 369                         data->max_brightness = num_levels;
 370                 }
 371
 372                 data->max_brightness--;
 373         }
 374
 375         return 0;
 376 }
 377
 378 static const struct of_device_id pwm_backlight_of_match[] = {
 379         { .compatible = "pwm-backlight" },
 380         { }
 381 };
 382
 383 MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
 384 #else
 385 static int pwm_backlight_parse_dt(struct device *dev,
 386                                   struct platform_pwm_backlight_data *data)
 387 {
 388         return -ENODEV;
 389 }
 390
 391 static
 392 int pwm_backlight_brightness_default(struct device *dev,
 393                                      struct platform_pwm_backlight_data *data,
 394                                      unsigned int period)
 395 {
 396         return -ENODEV;
 397 }
 398 #endif
 399
 400 static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
 401 {
 402         struct device_node *node = pb->dev->of_node;
 403         bool active = true;
 404
 405         /*
 406          * If the enable GPIO is present, observable (either as input
 407          * or output) and off then the backlight is not currently active.
 408          * */
 409         if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0)
 410                 active = false;
 411
 412         if (!regulator_is_enabled(pb->power_supply))
 413                 active = false;
 414
 415         if (!pwm_is_enabled(pb->pwm))
 416                 active = false;
 417
 418         /*
 419          * Synchronize the enable_gpio with the observed state of the
 420          * hardware.
 421          */
 422         if (pb->enable_gpio)
 423                 gpiod_direction_output(pb->enable_gpio, active);
 424
 425         /*
 426          * Do not change pb->enabled here! pb->enabled essentially
 427          * tells us if we own one of the regulator's use counts and
 428          * right now we do not.
 429          */
 430
 431         /* Not booted with device tree or no phandle link to the node */
 432         if (!node || !node->phandle)
 433                 return FB_BLANK_UNBLANK;
 434
 435         /*
 436          * If the driver is probed from the device tree and there is a
 437          * phandle link pointing to the backlight node, it is safe to
 438          * assume that another driver will enable the backlight at the
 439          * appropriate time. Therefore, if it is disabled, keep it so.
 440          */
 441         return active ? FB_BLANK_UNBLANK: FB_BLANK_POWERDOWN;
 442 }
 443
 444 static int pwm_backlight_probe(struct platform_device *pdev)
 445 {
 446         struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
 447         struct platform_pwm_backlight_data defdata;
 448         struct backlight_properties props;
 449         struct backlight_device *bl;
 450         struct device_node *node = pdev->dev.of_node;
 451         struct pwm_bl_data *pb;
 452         struct pwm_state state;
 453         struct pwm_args pargs;
 454         unsigned int i;
 455         int ret;
 456
 457         if (!data) {
 458                 ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
 459                 if (ret < 0) {
 460                         dev_err(&pdev->dev, "failed to find platform data\n");
 461                         return ret;
 462                 }
 463
 464                 data = &defdata;
 465         }
 466
 467         if (data->init) {
 468                 ret = data->init(&pdev->dev);
 469                 if (ret < 0)
 470                         return ret;
 471         }
 472
 473         pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
 474         if (!pb) {
 475                 ret = -ENOMEM;
 476                 goto err_alloc;
 477         }
 478
 479         pb->notify = data->notify;
 480         pb->notify_after = data->notify_after;
 481         pb->check_fb = data->check_fb;
 482         pb->exit = data->exit;
 483         pb->dev = &pdev->dev;
 484         pb->enabled = false;
 485         pb->post_pwm_on_delay = data->post_pwm_on_delay;
 486         pb->pwm_off_delay = data->pwm_off_delay;
 487
 488         pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
 489                                                   GPIOD_ASIS);
 490         if (IS_ERR(pb->enable_gpio)) {
 491                 ret = PTR_ERR(pb->enable_gpio);
 492                 goto err_alloc;
 493         }
 494
 495         /*
 496          * Compatibility fallback for drivers still using the integer GPIO
 497          * platform data. Must go away soon.
 498          */
 499         if (!pb->enable_gpio && gpio_is_valid(data->enable_gpio)) {
 500                 ret = devm_gpio_request_one(&pdev->dev, data->enable_gpio,
 501                                             GPIOF_OUT_INIT_HIGH, "enable");
 502                 if (ret < 0) {
 503                         dev_err(&pdev->dev, "failed to request GPIO#%d: %d\n",
 504                                 data->enable_gpio, ret);
 505                         goto err_alloc;
 506                 }
 507
 508                 pb->enable_gpio = gpio_to_desc(data->enable_gpio);
 509         }
 510
 511         pb->power_supply = devm_regulator_get(&pdev->dev, "power");
 512         if (IS_ERR(pb->power_supply)) {
 513                 ret = PTR_ERR(pb->power_supply);
 514                 goto err_alloc;
 515         }
 516
 517         pb->pwm = devm_pwm_get(&pdev->dev, NULL);
 518         if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) {
 519                 dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
 520                 pb->legacy = true;
 521                 pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
 522         }
 523
 524         if (IS_ERR(pb->pwm)) {
 525                 ret = PTR_ERR(pb->pwm);
 526                 if (ret != -EPROBE_DEFER)
 527                         dev_err(&pdev->dev, "unable to request PWM\n");
 528                 goto err_alloc;
 529         }
 530
 531         dev_dbg(&pdev->dev, "got pwm for backlight\n");
 532
 533         if (!data->levels) {
 534                 /* Get the PWM period (in nanoseconds) */
 535                 pwm_get_state(pb->pwm, &state);
 536
 537                 ret = pwm_backlight_brightness_default(&pdev->dev, data,
 538                                                        state.period);
 539                 if (ret < 0) {
 540                         dev_err(&pdev->dev,
 541                                 "failed to setup default brightness table\n");
 542                         goto err_alloc;
 543                 }
 544         }
 545
 546         for (i = 0; i <= data->max_brightness; i++) {
 547                 if (data->levels[i] > pb->scale)
 548                         pb->scale = data->levels[i];
 549
 550                 pb->levels = data->levels;
 551         }
 552
 553         /*
 554          * FIXME: pwm_apply_args() should be removed when switching to
 555          * the atomic PWM API.
 556          */
 557         pwm_apply_args(pb->pwm);
 558
 559         /*
 560          * The DT case will set the pwm_period_ns field to 0 and store the
 561          * period, parsed from the DT, in the PWM device. For the non-DT case,
 562          * set the period from platform data if it has not already been set
 563          * via the PWM lookup table.
 564          */
 565         pwm_get_args(pb->pwm, &pargs);
 566         pb->period = pargs.period;
 567         if (!pb->period && (data->pwm_period_ns > 0))
 568                 pb->period = data->pwm_period_ns;
 569
 570         pb->lth_brightness = data->lth_brightness * (pb->period / pb->scale);
 571
 572         memset(&props, 0, sizeof(struct backlight_properties));
 573         props.type = BACKLIGHT_RAW;
 574         props.max_brightness = data->max_brightness;
 575         bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
 576                                        &pwm_backlight_ops, &props);
 577         if (IS_ERR(bl)) {
 578                 dev_err(&pdev->dev, "failed to register backlight\n");
 579                 ret = PTR_ERR(bl);
 580                 if (pb->legacy)
 581                         pwm_free(pb->pwm);
 582                 goto err_alloc;
 583         }
 584
 585         if (data->dft_brightness > data->max_brightness) {
 586                 dev_warn(&pdev->dev,
 587                          "invalid default brightness level: %u, using %u\n",
 588                          data->dft_brightness, data->max_brightness);
 589                 data->dft_brightness = data->max_brightness;
 590         }
 591
 592         bl->props.brightness = data->dft_brightness;
 593         bl->props.power = pwm_backlight_initial_power_state(pb);
 594         backlight_update_status(bl);
 595
 596         platform_set_drvdata(pdev, bl);
 597         return 0;
 598
 599 err_alloc:
 600         if (data->exit)
 601                 data->exit(&pdev->dev);
 602         return ret;
 603 }
 604
 605 static int pwm_backlight_remove(struct platform_device *pdev)
 606 {
 607         struct backlight_device *bl = platform_get_drvdata(pdev);
 608         struct pwm_bl_data *pb = bl_get_data(bl);
 609
 610         backlight_device_unregister(bl);
 611         pwm_backlight_power_off(pb);
 612
 613         if (pb->exit)
 614                 pb->exit(&pdev->dev);
 615         if (pb->legacy)
 616                 pwm_free(pb->pwm);
 617
 618         return 0;
 619 }
 620
 621 static void pwm_backlight_shutdown(struct platform_device *pdev)
 622 {
 623         struct backlight_device *bl = platform_get_drvdata(pdev);
 624         struct pwm_bl_data *pb = bl_get_data(bl);
 625
 626         pwm_backlight_power_off(pb);
 627 }
 628
 629 #ifdef CONFIG_PM_SLEEP
 630 static int pwm_backlight_suspend(struct device *dev)
 631 {
 632         struct backlight_device *bl = dev_get_drvdata(dev);
 633         struct pwm_bl_data *pb = bl_get_data(bl);
 634
 635         if (pb->notify)
 636                 pb->notify(pb->dev, 0);
 637
 638         pwm_backlight_power_off(pb);
 639
 640         if (pb->notify_after)
 641                 pb->notify_after(pb->dev, 0);
 642
 643         return 0;
 644 }
 645
 646 static int pwm_backlight_resume(struct device *dev)
 647 {
 648         struct backlight_device *bl = dev_get_drvdata(dev);
 649
 650         backlight_update_status(bl);
 651
 652         return 0;
 653 }
 654 #endif
 655
 656 static const struct dev_pm_ops pwm_backlight_pm_ops = {
 657 #ifdef CONFIG_PM_SLEEP
 658         .suspend = pwm_backlight_suspend,
 659         .resume = pwm_backlight_resume,
 660         .poweroff = pwm_backlight_suspend,
 661         .restore = pwm_backlight_resume,
 662 #endif
 663 };
 664
 665 static struct platform_driver pwm_backlight_driver = {
 666         .driver         = {
 667                 .name           = "pwm-backlight",
 668                 .pm             = &pwm_backlight_pm_ops,
 669                 .of_match_table = of_match_ptr(pwm_backlight_of_match),
 670         },
 671         .probe          = pwm_backlight_probe,
 672         .remove         = pwm_backlight_remove,
 673         .shutdown       = pwm_backlight_shutdown,
 674 };
 675
 676 module_platform_driver(pwm_backlight_driver);
 677
 678 MODULE_DESCRIPTION("PWM based Backlight Driver");
 679 MODULE_LICENSE("GPL");
 680 MODULE_ALIAS("platform:pwm-backlight");