drivers/video/backlight/pwm_bl.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Simple PWM based backlight control, board code has to setup
   4  * 1) pin configuration so PWM waveforms can output
   5  * 2) platform_data being correctly configured
   6  */
   7
   8 #include <linux/delay.h>
   9 #include <linux/gpio/consumer.h>
  10 #include <linux/module.h>
  11 #include <linux/kernel.h>
  12 #include <linux/init.h>
  13 #include <linux/platform_device.h>
  14 #include <linux/fb.h>
  15 #include <linux/backlight.h>
  16 #include <linux/err.h>
  17 #include <linux/pwm.h>
  18 #include <linux/pwm_backlight.h>
  19 #include <linux/regulator/consumer.h>
  20 #include <linux/slab.h>
  21
  22 struct pwm_bl_data {
  23         struct pwm_device       *pwm;
  24         struct device           *dev;
  25         unsigned int            lth_brightness;
  26         unsigned int            *levels;
  27         bool                    enabled;
  28         struct regulator        *power_supply;
  29         struct gpio_desc        *enable_gpio;
  30         unsigned int            scale;
  31         unsigned int            post_pwm_on_delay;
  32         unsigned int            pwm_off_delay;
  33         int                     (*notify)(struct device *,
  34                                           int brightness);
  35         void                    (*notify_after)(struct device *,
  36                                         int brightness);
  37         int                     (*check_fb)(struct device *, struct fb_info *);
  38         void                    (*exit)(struct device *);
  39 };
  40
  41 static void pwm_backlight_power_on(struct pwm_bl_data *pb)
  42 {
  43         int err;
  44
  45         if (pb->enabled)
  46                 return;
  47
  48         if (pb->power_supply) {
  49                 err = regulator_enable(pb->power_supply);
  50                 if (err < 0)
  51                         dev_err(pb->dev, "failed to enable power supply\n");
  52         }
  53
  54         if (pb->post_pwm_on_delay)
  55                 msleep(pb->post_pwm_on_delay);
  56
  57         gpiod_set_value_cansleep(pb->enable_gpio, 1);
  58
  59         pb->enabled = true;
  60 }
  61
  62 static void pwm_backlight_power_off(struct pwm_bl_data *pb)
  63 {
  64         if (!pb->enabled)
  65                 return;
  66
  67         gpiod_set_value_cansleep(pb->enable_gpio, 0);
  68
  69         if (pb->pwm_off_delay)
  70                 msleep(pb->pwm_off_delay);
  71
  72         if (pb->power_supply)
  73                 regulator_disable(pb->power_supply);
  74         pb->enabled = false;
  75 }
  76
  77 static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness, struct pwm_state *state)
  78 {
  79         unsigned int lth = pb->lth_brightness;
  80         u64 duty_cycle;
  81
  82         if (pb->levels)
  83                 duty_cycle = pb->levels[brightness];
  84         else
  85                 duty_cycle = brightness;
  86
  87         duty_cycle *= state->period - lth;
  88         do_div(duty_cycle, pb->scale);
  89
  90         return duty_cycle + lth;
  91 }
  92
  93 static int pwm_backlight_update_status(struct backlight_device *bl)
  94 {
  95         struct pwm_bl_data *pb = bl_get_data(bl);
  96         int brightness = backlight_get_brightness(bl);
  97         struct pwm_state state;
  98
  99         if (pb->notify)
 100                 brightness = pb->notify(pb->dev, brightness);
 101
 102         if (brightness > 0) {
 103                 pwm_get_state(pb->pwm, &state);
 104                 state.duty_cycle = compute_duty_cycle(pb, brightness, &state);
 105                 state.enabled = true;
 106                 pwm_apply_state(pb->pwm, &state);
 107
 108                 pwm_backlight_power_on(pb);
 109         } else {
 110                 pwm_backlight_power_off(pb);
 111
 112                 pwm_get_state(pb->pwm, &state);
 113                 state.duty_cycle = 0;
 114                 /*
 115                  * We cannot assume a disabled PWM to drive its output to the
 116                  * inactive state. If we have an enable GPIO and/or a regulator
 117                  * we assume that this isn't relevant and we can disable the PWM
 118                  * to save power. If however there is neither an enable GPIO nor
 119                  * a regulator keep the PWM on be sure to get a constant
 120                  * inactive output.
 121                  */
 122                 state.enabled = !pb->power_supply && !pb->enable_gpio;
 123                 pwm_apply_state(pb->pwm, &state);
 124         }
 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_SHIFT     16
 147 #define PWM_LUMINANCE_SCALE     (1 << PWM_LUMINANCE_SHIFT) /* luminance scale */
 148
 149 /*
 150  * CIE lightness to PWM conversion.
 151  *
 152  * The CIE 1931 lightness formula is what actually describes how we perceive
 153  * light:
 154  *          Y = (L* / 903.3)           if L* ≤ 8
 155  *          Y = ((L* + 16) / 116)^3    if L* > 8
 156  *
 157  * Where Y is the luminance, the amount of light coming out of the screen, and
 158  * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
 159  * perceives the screen to be, and is a number between 0 and 100.
 160  *
 161  * The following function does the fixed point maths needed to implement the
 162  * above formula.
 163  */
 164 static u64 cie1931(unsigned int lightness)
 165 {
 166         u64 retval;
 167
 168         /*
 169          * @lightness is given as a number between 0 and 1, expressed
 170          * as a fixed-point number in scale
 171          * PWM_LUMINANCE_SCALE. Convert to a percentage, still
 172          * expressed as a fixed-point number, so the above formulas
 173          * can be applied.
 174          */
 175         lightness *= 100;
 176         if (lightness <= (8 * PWM_LUMINANCE_SCALE)) {
 177                 retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
 178         } else {
 179                 retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116;
 180                 retval *= retval * retval;
 181                 retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1);
 182                 retval >>= 2*PWM_LUMINANCE_SHIFT;
 183         }
 184
 185         return retval;
 186 }
 187
 188 /*
 189  * Create a default correction table for PWM values to create linear brightness
 190  * for LED based backlights using the CIE1931 algorithm.
 191  */
 192 static
 193 int pwm_backlight_brightness_default(struct device *dev,
 194                                      struct platform_pwm_backlight_data *data,
 195                                      unsigned int period)
 196 {
 197         unsigned int i;
 198         u64 retval;
 199
 200         /*
 201          * Once we have 4096 levels there's little point going much higher...
 202          * neither interactive sliders nor animation benefits from having
 203          * more values in the table.
 204          */
 205         data->max_brightness =
 206                 min((int)DIV_ROUND_UP(period, fls(period)), 4096);
 207
 208         data->levels = devm_kcalloc(dev, data->max_brightness,
 209                                     sizeof(*data->levels), GFP_KERNEL);
 210         if (!data->levels)
 211                 return -ENOMEM;
 212
 213         /* Fill the table using the cie1931 algorithm */
 214         for (i = 0; i < data->max_brightness; i++) {
 215                 retval = cie1931((i * PWM_LUMINANCE_SCALE) /
 216                                  data->max_brightness) * period;
 217                 retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
 218                 if (retval > UINT_MAX)
 219                         return -EINVAL;
 220                 data->levels[i] = (unsigned int)retval;
 221         }
 222
 223         data->dft_brightness = data->max_brightness / 2;
 224         data->max_brightness--;
 225
 226         return 0;
 227 }
 228
 229 static int pwm_backlight_parse_dt(struct device *dev,
 230                                   struct platform_pwm_backlight_data *data)
 231 {
 232         struct device_node *node = dev->of_node;
 233         unsigned int num_levels;
 234         unsigned int num_steps = 0;
 235         struct property *prop;
 236         unsigned int *table;
 237         int length;
 238         u32 value;
 239         int ret;
 240
 241         if (!node)
 242                 return -ENODEV;
 243
 244         memset(data, 0, sizeof(*data));
 245
 246         /*
 247          * These values are optional and set as 0 by default, the out values
 248          * are modified only if a valid u32 value can be decoded.
 249          */
 250         of_property_read_u32(node, "post-pwm-on-delay-ms",
 251                              &data->post_pwm_on_delay);
 252         of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay);
 253
 254         /*
 255          * Determine the number of brightness levels, if this property is not
 256          * set a default table of brightness levels will be used.
 257          */
 258         prop = of_find_property(node, "brightness-levels", &length);
 259         if (!prop)
 260                 return 0;
 261
 262         num_levels = length / sizeof(u32);
 263
 264         /* read brightness levels from DT property */
 265         if (num_levels > 0) {
 266                 data->levels = devm_kcalloc(dev, num_levels,
 267                                             sizeof(*data->levels), GFP_KERNEL);
 268                 if (!data->levels)
 269                         return -ENOMEM;
 270
 271                 ret = of_property_read_u32_array(node, "brightness-levels",
 272                                                  data->levels,
 273                                                  num_levels);
 274                 if (ret < 0)
 275                         return ret;
 276
 277                 ret = of_property_read_u32(node, "default-brightness-level",
 278                                            &value);
 279                 if (ret < 0)
 280                         return ret;
 281
 282                 data->dft_brightness = value;
 283
 284                 /*
 285                  * This property is optional, if is set enables linear
 286                  * interpolation between each of the values of brightness levels
 287                  * and creates a new pre-computed table.
 288                  */
 289                 of_property_read_u32(node, "num-interpolated-steps",
 290                                      &num_steps);
 291
 292                 /*
 293                  * Make sure that there is at least two entries in the
 294                  * brightness-levels table, otherwise we can't interpolate
 295                  * between two points.
 296                  */
 297                 if (num_steps) {
 298                         unsigned int num_input_levels = num_levels;
 299                         unsigned int i;
 300                         u32 x1, x2, x, dx;
 301                         u32 y1, y2;
 302                         s64 dy;
 303
 304                         if (num_input_levels < 2) {
 305                                 dev_err(dev, "can't interpolate\n");
 306                                 return -EINVAL;
 307                         }
 308
 309                         /*
 310                          * Recalculate the number of brightness levels, now
 311                          * taking in consideration the number of interpolated
 312                          * steps between two levels.
 313                          */
 314                         num_levels = (num_input_levels - 1) * num_steps + 1;
 315                         dev_dbg(dev, "new number of brightness levels: %d\n",
 316                                 num_levels);
 317
 318                         /*
 319                          * Create a new table of brightness levels with all the
 320                          * interpolated steps.
 321                          */
 322                         table = devm_kcalloc(dev, num_levels, sizeof(*table),
 323                                              GFP_KERNEL);
 324                         if (!table)
 325                                 return -ENOMEM;
 326                         /*
 327                          * Fill the interpolated table[x] = y
 328                          * by draw lines between each (x1, y1) to (x2, y2).
 329                          */
 330                         dx = num_steps;
 331                         for (i = 0; i < num_input_levels - 1; i++) {
 332                                 x1 = i * dx;
 333                                 x2 = x1 + dx;
 334                                 y1 = data->levels[i];
 335                                 y2 = data->levels[i + 1];
 336                                 dy = (s64)y2 - y1;
 337
 338                                 for (x = x1; x < x2; x++) {
 339                                         table[x] = y1 +
 340                                                 div_s64(dy * (x - x1), dx);
 341                                 }
 342                         }
 343                         /* Fill in the last point, since no line starts here. */
 344                         table[x2] = y2;
 345
 346                         /*
 347                          * As we use interpolation lets remove current
 348                          * brightness levels table and replace for the
 349                          * new interpolated table.
 350                          */
 351                         devm_kfree(dev, data->levels);
 352                         data->levels = table;
 353                 }
 354
 355                 data->max_brightness = num_levels - 1;
 356         }
 357
 358         return 0;
 359 }
 360
 361 static const struct of_device_id pwm_backlight_of_match[] = {
 362         { .compatible = "pwm-backlight" },
 363         { }
 364 };
 365
 366 MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
 367 #else
 368 static int pwm_backlight_parse_dt(struct device *dev,
 369                                   struct platform_pwm_backlight_data *data)
 370 {
 371         return -ENODEV;
 372 }
 373
 374 static
 375 int pwm_backlight_brightness_default(struct device *dev,
 376                                      struct platform_pwm_backlight_data *data,
 377                                      unsigned int period)
 378 {
 379         return -ENODEV;
 380 }
 381 #endif
 382
 383 static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data)
 384 {
 385         unsigned int nlevels = data->max_brightness + 1;
 386         unsigned int min_val = data->levels[0];
 387         unsigned int max_val = data->levels[nlevels - 1];
 388         /*
 389          * Multiplying by 128 means that even in pathological cases such
 390          * as (max_val - min_val) == nlevels the error at max_val is less
 391          * than 1%.
 392          */
 393         unsigned int slope = (128 * (max_val - min_val)) / nlevels;
 394         unsigned int margin = (max_val - min_val) / 20; /* 5% */
 395         int i;
 396
 397         for (i = 1; i < nlevels; i++) {
 398                 unsigned int linear_value = min_val + ((i * slope) / 128);
 399                 unsigned int delta = abs(linear_value - data->levels[i]);
 400
 401                 if (delta > margin)
 402                         return false;
 403         }
 404
 405         return true;
 406 }
 407
 408 static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
 409 {
 410         struct device_node *node = pb->dev->of_node;
 411         bool active = true;
 412
 413         /*
 414          * If the enable GPIO is present, observable (either as input
 415          * or output) and off then the backlight is not currently active.
 416          * */
 417         if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0)
 418                 active = false;
 419
 420         if (pb->power_supply && !regulator_is_enabled(pb->power_supply))
 421                 active = false;
 422
 423         if (!pwm_is_enabled(pb->pwm))
 424                 active = false;
 425
 426         /*
 427          * Synchronize the enable_gpio with the observed state of the
 428          * hardware.
 429          */
 430         gpiod_direction_output(pb->enable_gpio, active);
 431
 432         /*
 433          * Do not change pb->enabled here! pb->enabled essentially
 434          * tells us if we own one of the regulator's use counts and
 435          * right now we do not.
 436          */
 437
 438         /* Not booted with device tree or no phandle link to the node */
 439         if (!node || !node->phandle)
 440                 return FB_BLANK_UNBLANK;
 441
 442         /*
 443          * If the driver is probed from the device tree and there is a
 444          * phandle link pointing to the backlight node, it is safe to
 445          * assume that another driver will enable the backlight at the
 446          * appropriate time. Therefore, if it is disabled, keep it so.
 447          */
 448         return active ? FB_BLANK_UNBLANK: FB_BLANK_POWERDOWN;
 449 }
 450
 451 static int pwm_backlight_probe(struct platform_device *pdev)
 452 {
 453         struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
 454         struct platform_pwm_backlight_data defdata;
 455         struct backlight_properties props;
 456         struct backlight_device *bl;
 457         struct pwm_bl_data *pb;
 458         struct pwm_state state;
 459         unsigned int i;
 460         int ret;
 461
 462         if (!data) {
 463                 ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
 464                 if (ret < 0) {
 465                         dev_err(&pdev->dev, "failed to find platform data\n");
 466                         return ret;
 467                 }
 468
 469                 data = &defdata;
 470         }
 471
 472         if (data->init) {
 473                 ret = data->init(&pdev->dev);
 474                 if (ret < 0)
 475                         return ret;
 476         }
 477
 478         pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
 479         if (!pb) {
 480                 ret = -ENOMEM;
 481                 goto err_alloc;
 482         }
 483
 484         pb->notify = data->notify;
 485         pb->notify_after = data->notify_after;
 486         pb->check_fb = data->check_fb;
 487         pb->exit = data->exit;
 488         pb->dev = &pdev->dev;
 489         pb->enabled = false;
 490         pb->post_pwm_on_delay = data->post_pwm_on_delay;
 491         pb->pwm_off_delay = data->pwm_off_delay;
 492
 493         pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
 494                                                   GPIOD_ASIS);
 495         if (IS_ERR(pb->enable_gpio)) {
 496                 ret = PTR_ERR(pb->enable_gpio);
 497                 goto err_alloc;
 498         }
 499
 500         pb->power_supply = devm_regulator_get_optional(&pdev->dev, "power");
 501         if (IS_ERR(pb->power_supply)) {
 502                 ret = PTR_ERR(pb->power_supply);
 503                 if (ret == -ENODEV)
 504                         pb->power_supply = NULL;
 505                 else
 506                         goto err_alloc;
 507         }
 508
 509         pb->pwm = devm_pwm_get(&pdev->dev, NULL);
 510         if (IS_ERR(pb->pwm)) {
 511                 ret = PTR_ERR(pb->pwm);
 512                 if (ret != -EPROBE_DEFER)
 513                         dev_err(&pdev->dev, "unable to request PWM\n");
 514                 goto err_alloc;
 515         }
 516
 517         dev_dbg(&pdev->dev, "got pwm for backlight\n");
 518
 519         /* Sync up PWM state. */
 520         pwm_init_state(pb->pwm, &state);
 521
 522         /*
 523          * The DT case will set the pwm_period_ns field to 0 and store the
 524          * period, parsed from the DT, in the PWM device. For the non-DT case,
 525          * set the period from platform data if it has not already been set
 526          * via the PWM lookup table.
 527          */
 528         if (!state.period && (data->pwm_period_ns > 0))
 529                 state.period = data->pwm_period_ns;
 530
 531         ret = pwm_apply_state(pb->pwm, &state);
 532         if (ret) {
 533                 dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
 534                         ret);
 535                 goto err_alloc;
 536         }
 537
 538         memset(&props, 0, sizeof(struct backlight_properties));
 539
 540         if (data->levels) {
 541                 pb->levels = data->levels;
 542
 543                 /*
 544                  * For the DT case, only when brightness levels is defined
 545                  * data->levels is filled. For the non-DT case, data->levels
 546                  * can come from platform data, however is not usual.
 547                  */
 548                 for (i = 0; i <= data->max_brightness; i++)
 549                         if (data->levels[i] > pb->scale)
 550                                 pb->scale = data->levels[i];
 551
 552                 if (pwm_backlight_is_linear(data))
 553                         props.scale = BACKLIGHT_SCALE_LINEAR;
 554                 else
 555                         props.scale = BACKLIGHT_SCALE_NON_LINEAR;
 556         } else if (!data->max_brightness) {
 557                 /*
 558                  * If no brightness levels are provided and max_brightness is
 559                  * not set, use the default brightness table. For the DT case,
 560                  * max_brightness is set to 0 when brightness levels is not
 561                  * specified. For the non-DT case, max_brightness is usually
 562                  * set to some value.
 563                  */
 564
 565                 /* Get the PWM period (in nanoseconds) */
 566                 pwm_get_state(pb->pwm, &state);
 567
 568                 ret = pwm_backlight_brightness_default(&pdev->dev, data,
 569                                                        state.period);
 570                 if (ret < 0) {
 571                         dev_err(&pdev->dev,
 572                                 "failed to setup default brightness table\n");
 573                         goto err_alloc;
 574                 }
 575
 576                 for (i = 0; i <= data->max_brightness; i++) {
 577                         if (data->levels[i] > pb->scale)
 578                                 pb->scale = data->levels[i];
 579
 580                         pb->levels = data->levels;
 581                 }
 582
 583                 props.scale = BACKLIGHT_SCALE_NON_LINEAR;
 584         } else {
 585                 /*
 586                  * That only happens for the non-DT case, where platform data
 587                  * sets the max_brightness value.
 588                  */
 589                 pb->scale = data->max_brightness;
 590         }
 591
 592         pb->lth_brightness = data->lth_brightness * (div_u64(state.period,
 593                                 pb->scale));
 594
 595         props.type = BACKLIGHT_RAW;
 596         props.max_brightness = data->max_brightness;
 597         bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
 598                                        &pwm_backlight_ops, &props);
 599         if (IS_ERR(bl)) {
 600                 dev_err(&pdev->dev, "failed to register backlight\n");
 601                 ret = PTR_ERR(bl);
 602                 goto err_alloc;
 603         }
 604
 605         if (data->dft_brightness > data->max_brightness) {
 606                 dev_warn(&pdev->dev,
 607                          "invalid default brightness level: %u, using %u\n",
 608                          data->dft_brightness, data->max_brightness);
 609                 data->dft_brightness = data->max_brightness;
 610         }
 611
 612         bl->props.brightness = data->dft_brightness;
 613         bl->props.power = pwm_backlight_initial_power_state(pb);
 614         backlight_update_status(bl);
 615
 616         platform_set_drvdata(pdev, bl);
 617         return 0;
 618
 619 err_alloc:
 620         if (data->exit)
 621                 data->exit(&pdev->dev);
 622         return ret;
 623 }
 624
 625 static void pwm_backlight_remove(struct platform_device *pdev)
 626 {
 627         struct backlight_device *bl = platform_get_drvdata(pdev);
 628         struct pwm_bl_data *pb = bl_get_data(bl);
 629
 630         backlight_device_unregister(bl);
 631         pwm_backlight_power_off(pb);
 632
 633         if (pb->exit)
 634                 pb->exit(&pdev->dev);
 635 }
 636
 637 static void pwm_backlight_shutdown(struct platform_device *pdev)
 638 {
 639         struct backlight_device *bl = platform_get_drvdata(pdev);
 640         struct pwm_bl_data *pb = bl_get_data(bl);
 641
 642         pwm_backlight_power_off(pb);
 643 }
 644
 645 #ifdef CONFIG_PM_SLEEP
 646 static int pwm_backlight_suspend(struct device *dev)
 647 {
 648         struct backlight_device *bl = dev_get_drvdata(dev);
 649         struct pwm_bl_data *pb = bl_get_data(bl);
 650
 651         if (pb->notify)
 652                 pb->notify(pb->dev, 0);
 653
 654         pwm_backlight_power_off(pb);
 655
 656         if (pb->notify_after)
 657                 pb->notify_after(pb->dev, 0);
 658
 659         return 0;
 660 }
 661
 662 static int pwm_backlight_resume(struct device *dev)
 663 {
 664         struct backlight_device *bl = dev_get_drvdata(dev);
 665
 666         backlight_update_status(bl);
 667
 668         return 0;
 669 }
 670 #endif
 671
 672 static const struct dev_pm_ops pwm_backlight_pm_ops = {
 673 #ifdef CONFIG_PM_SLEEP
 674         .suspend = pwm_backlight_suspend,
 675         .resume = pwm_backlight_resume,
 676         .poweroff = pwm_backlight_suspend,
 677         .restore = pwm_backlight_resume,
 678 #endif
 679 };
 680
 681 static struct platform_driver pwm_backlight_driver = {
 682         .driver         = {
 683                 .name           = "pwm-backlight",
 684                 .pm             = &pwm_backlight_pm_ops,
 685                 .of_match_table = of_match_ptr(pwm_backlight_of_match),
 686         },
 687         .probe          = pwm_backlight_probe,
 688         .remove_new     = pwm_backlight_remove,
 689         .shutdown       = pwm_backlight_shutdown,
 690 };
 691
 692 module_platform_driver(pwm_backlight_driver);
 693
 694 MODULE_DESCRIPTION("PWM based Backlight Driver");
 695 MODULE_LICENSE("GPL v2");
 696 MODULE_ALIAS("platform:pwm-backlight");