xref: /openbmc/linux/drivers/video/backlight/pwm_bl.c (revision a10c3d5f)
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 
pwm_backlight_power_on(struct pwm_bl_data * pb)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 
pwm_backlight_power_off(struct pwm_bl_data * pb)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 
compute_duty_cycle(struct pwm_bl_data * pb,int brightness,struct pwm_state * state)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 
pwm_backlight_update_status(struct backlight_device * bl)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_might_sleep(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_might_sleep(pb->pwm, &state);
124 	}
125 
126 	if (pb->notify_after)
127 		pb->notify_after(pb->dev, brightness);
128 
129 	return 0;
130 }
131 
pwm_backlight_check_fb(struct backlight_device * bl,struct fb_info * info)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  */
cie1931(unsigned int lightness)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
pwm_backlight_brightness_default(struct device * dev,struct platform_pwm_backlight_data * data,unsigned int period)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 
pwm_backlight_parse_dt(struct device * dev,struct platform_pwm_backlight_data * data)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
pwm_backlight_parse_dt(struct device * dev,struct platform_pwm_backlight_data * data)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
pwm_backlight_brightness_default(struct device * dev,struct platform_pwm_backlight_data * data,unsigned int period)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 
pwm_backlight_is_linear(struct platform_pwm_backlight_data * data)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 
pwm_backlight_initial_power_state(const struct pwm_bl_data * pb)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 
pwm_backlight_probe(struct platform_device * pdev)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_might_sleep(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 
pwm_backlight_remove(struct platform_device * pdev)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 	struct pwm_state state;
630 
631 	backlight_device_unregister(bl);
632 	pwm_backlight_power_off(pb);
633 	pwm_get_state(pb->pwm, &state);
634 	state.duty_cycle = 0;
635 	state.enabled = false;
636 	pwm_apply_might_sleep(pb->pwm, &state);
637 
638 	if (pb->exit)
639 		pb->exit(&pdev->dev);
640 }
641 
pwm_backlight_shutdown(struct platform_device * pdev)642 static void pwm_backlight_shutdown(struct platform_device *pdev)
643 {
644 	struct backlight_device *bl = platform_get_drvdata(pdev);
645 	struct pwm_bl_data *pb = bl_get_data(bl);
646 	struct pwm_state state;
647 
648 	pwm_backlight_power_off(pb);
649 	pwm_get_state(pb->pwm, &state);
650 	state.duty_cycle = 0;
651 	state.enabled = false;
652 	pwm_apply_might_sleep(pb->pwm, &state);
653 }
654 
655 #ifdef CONFIG_PM_SLEEP
pwm_backlight_suspend(struct device * dev)656 static int pwm_backlight_suspend(struct device *dev)
657 {
658 	struct backlight_device *bl = dev_get_drvdata(dev);
659 	struct pwm_bl_data *pb = bl_get_data(bl);
660 	struct pwm_state state;
661 
662 	if (pb->notify)
663 		pb->notify(pb->dev, 0);
664 
665 	pwm_backlight_power_off(pb);
666 
667 	/*
668 	 * Note that disabling the PWM doesn't guarantee that the output stays
669 	 * at its inactive state. However without the PWM disabled, the PWM
670 	 * driver refuses to suspend. So disable here even though this might
671 	 * enable the backlight on poorly designed boards.
672 	 */
673 	pwm_get_state(pb->pwm, &state);
674 	state.duty_cycle = 0;
675 	state.enabled = false;
676 	pwm_apply_might_sleep(pb->pwm, &state);
677 
678 	if (pb->notify_after)
679 		pb->notify_after(pb->dev, 0);
680 
681 	return 0;
682 }
683 
pwm_backlight_resume(struct device * dev)684 static int pwm_backlight_resume(struct device *dev)
685 {
686 	struct backlight_device *bl = dev_get_drvdata(dev);
687 
688 	backlight_update_status(bl);
689 
690 	return 0;
691 }
692 #endif
693 
694 static const struct dev_pm_ops pwm_backlight_pm_ops = {
695 #ifdef CONFIG_PM_SLEEP
696 	.suspend = pwm_backlight_suspend,
697 	.resume = pwm_backlight_resume,
698 	.poweroff = pwm_backlight_suspend,
699 	.restore = pwm_backlight_resume,
700 #endif
701 };
702 
703 static struct platform_driver pwm_backlight_driver = {
704 	.driver		= {
705 		.name		= "pwm-backlight",
706 		.pm		= &pwm_backlight_pm_ops,
707 		.of_match_table	= of_match_ptr(pwm_backlight_of_match),
708 	},
709 	.probe		= pwm_backlight_probe,
710 	.remove_new	= pwm_backlight_remove,
711 	.shutdown	= pwm_backlight_shutdown,
712 };
713 
714 module_platform_driver(pwm_backlight_driver);
715 
716 MODULE_DESCRIPTION("PWM based Backlight Driver");
717 MODULE_LICENSE("GPL v2");
718 MODULE_ALIAS("platform:pwm-backlight");
719