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 if (pb->enable_gpio)
58 gpiod_set_value_cansleep(pb->enable_gpio, 1);
59
60 pb->enabled = true;
61 }
62
pwm_backlight_power_off(struct pwm_bl_data * pb)63 static void pwm_backlight_power_off(struct pwm_bl_data *pb)
64 {
65 if (!pb->enabled)
66 return;
67
68 if (pb->enable_gpio)
69 gpiod_set_value_cansleep(pb->enable_gpio, 0);
70
71 if (pb->pwm_off_delay)
72 msleep(pb->pwm_off_delay);
73
74 if (pb->power_supply)
75 regulator_disable(pb->power_supply);
76 pb->enabled = false;
77 }
78
compute_duty_cycle(struct pwm_bl_data * pb,int brightness,struct pwm_state * state)79 static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness, struct pwm_state *state)
80 {
81 unsigned int lth = pb->lth_brightness;
82 u64 duty_cycle;
83
84 if (pb->levels)
85 duty_cycle = pb->levels[brightness];
86 else
87 duty_cycle = brightness;
88
89 duty_cycle *= state->period - lth;
90 do_div(duty_cycle, pb->scale);
91
92 return duty_cycle + lth;
93 }
94
pwm_backlight_update_status(struct backlight_device * bl)95 static int pwm_backlight_update_status(struct backlight_device *bl)
96 {
97 struct pwm_bl_data *pb = bl_get_data(bl);
98 int brightness = backlight_get_brightness(bl);
99 struct pwm_state state;
100
101 if (pb->notify)
102 brightness = pb->notify(pb->dev, brightness);
103
104 if (brightness > 0) {
105 pwm_get_state(pb->pwm, &state);
106 state.duty_cycle = compute_duty_cycle(pb, brightness, &state);
107 state.enabled = true;
108 pwm_apply_state(pb->pwm, &state);
109
110 pwm_backlight_power_on(pb);
111 } else {
112 pwm_backlight_power_off(pb);
113
114 pwm_get_state(pb->pwm, &state);
115 state.duty_cycle = 0;
116 /*
117 * We cannot assume a disabled PWM to drive its output to the
118 * inactive state. If we have an enable GPIO and/or a regulator
119 * we assume that this isn't relevant and we can disable the PWM
120 * to save power. If however there is neither an enable GPIO nor
121 * a regulator keep the PWM on be sure to get a constant
122 * inactive output.
123 */
124 state.enabled = !pb->power_supply && !pb->enable_gpio;
125 pwm_apply_state(pb->pwm, &state);
126 }
127
128 if (pb->notify_after)
129 pb->notify_after(pb->dev, brightness);
130
131 return 0;
132 }
133
pwm_backlight_check_fb(struct backlight_device * bl,struct fb_info * info)134 static int pwm_backlight_check_fb(struct backlight_device *bl,
135 struct fb_info *info)
136 {
137 struct pwm_bl_data *pb = bl_get_data(bl);
138
139 return !pb->check_fb || pb->check_fb(pb->dev, info);
140 }
141
142 static const struct backlight_ops pwm_backlight_ops = {
143 .update_status = pwm_backlight_update_status,
144 .check_fb = pwm_backlight_check_fb,
145 };
146
147 #ifdef CONFIG_OF
148 #define PWM_LUMINANCE_SHIFT 16
149 #define PWM_LUMINANCE_SCALE (1 << PWM_LUMINANCE_SHIFT) /* luminance scale */
150
151 /*
152 * CIE lightness to PWM conversion.
153 *
154 * The CIE 1931 lightness formula is what actually describes how we perceive
155 * light:
156 * Y = (L* / 903.3) if L* ≤ 8
157 * Y = ((L* + 16) / 116)^3 if L* > 8
158 *
159 * Where Y is the luminance, the amount of light coming out of the screen, and
160 * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
161 * perceives the screen to be, and is a number between 0 and 100.
162 *
163 * The following function does the fixed point maths needed to implement the
164 * above formula.
165 */
cie1931(unsigned int lightness)166 static u64 cie1931(unsigned int lightness)
167 {
168 u64 retval;
169
170 /*
171 * @lightness is given as a number between 0 and 1, expressed
172 * as a fixed-point number in scale
173 * PWM_LUMINANCE_SCALE. Convert to a percentage, still
174 * expressed as a fixed-point number, so the above formulas
175 * can be applied.
176 */
177 lightness *= 100;
178 if (lightness <= (8 * PWM_LUMINANCE_SCALE)) {
179 retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
180 } else {
181 retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116;
182 retval *= retval * retval;
183 retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1);
184 retval >>= 2*PWM_LUMINANCE_SHIFT;
185 }
186
187 return retval;
188 }
189
190 /*
191 * Create a default correction table for PWM values to create linear brightness
192 * for LED based backlights using the CIE1931 algorithm.
193 */
194 static
pwm_backlight_brightness_default(struct device * dev,struct platform_pwm_backlight_data * data,unsigned int period)195 int pwm_backlight_brightness_default(struct device *dev,
196 struct platform_pwm_backlight_data *data,
197 unsigned int period)
198 {
199 unsigned int i;
200 u64 retval;
201
202 /*
203 * Once we have 4096 levels there's little point going much higher...
204 * neither interactive sliders nor animation benefits from having
205 * more values in the table.
206 */
207 data->max_brightness =
208 min((int)DIV_ROUND_UP(period, fls(period)), 4096);
209
210 data->levels = devm_kcalloc(dev, data->max_brightness,
211 sizeof(*data->levels), GFP_KERNEL);
212 if (!data->levels)
213 return -ENOMEM;
214
215 /* Fill the table using the cie1931 algorithm */
216 for (i = 0; i < data->max_brightness; i++) {
217 retval = cie1931((i * PWM_LUMINANCE_SCALE) /
218 data->max_brightness) * period;
219 retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
220 if (retval > UINT_MAX)
221 return -EINVAL;
222 data->levels[i] = (unsigned int)retval;
223 }
224
225 data->dft_brightness = data->max_brightness / 2;
226 data->max_brightness--;
227
228 return 0;
229 }
230
pwm_backlight_parse_dt(struct device * dev,struct platform_pwm_backlight_data * data)231 static int pwm_backlight_parse_dt(struct device *dev,
232 struct platform_pwm_backlight_data *data)
233 {
234 struct device_node *node = dev->of_node;
235 unsigned int num_levels;
236 unsigned int num_steps = 0;
237 struct property *prop;
238 unsigned int *table;
239 int length;
240 u32 value;
241 int ret;
242
243 if (!node)
244 return -ENODEV;
245
246 memset(data, 0, sizeof(*data));
247
248 /*
249 * These values are optional and set as 0 by default, the out values
250 * are modified only if a valid u32 value can be decoded.
251 */
252 of_property_read_u32(node, "post-pwm-on-delay-ms",
253 &data->post_pwm_on_delay);
254 of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay);
255
256 /*
257 * Determine the number of brightness levels, if this property is not
258 * set a default table of brightness levels will be used.
259 */
260 prop = of_find_property(node, "brightness-levels", &length);
261 if (!prop)
262 return 0;
263
264 num_levels = length / sizeof(u32);
265
266 /* read brightness levels from DT property */
267 if (num_levels > 0) {
268 data->levels = devm_kcalloc(dev, num_levels,
269 sizeof(*data->levels), GFP_KERNEL);
270 if (!data->levels)
271 return -ENOMEM;
272
273 ret = of_property_read_u32_array(node, "brightness-levels",
274 data->levels,
275 num_levels);
276 if (ret < 0)
277 return ret;
278
279 ret = of_property_read_u32(node, "default-brightness-level",
280 &value);
281 if (ret < 0)
282 return ret;
283
284 data->dft_brightness = value;
285
286 /*
287 * This property is optional, if is set enables linear
288 * interpolation between each of the values of brightness levels
289 * and creates a new pre-computed table.
290 */
291 of_property_read_u32(node, "num-interpolated-steps",
292 &num_steps);
293
294 /*
295 * Make sure that there is at least two entries in the
296 * brightness-levels table, otherwise we can't interpolate
297 * between two points.
298 */
299 if (num_steps) {
300 unsigned int num_input_levels = num_levels;
301 unsigned int i;
302 u32 x1, x2, x, dx;
303 u32 y1, y2;
304 s64 dy;
305
306 if (num_input_levels < 2) {
307 dev_err(dev, "can't interpolate\n");
308 return -EINVAL;
309 }
310
311 /*
312 * Recalculate the number of brightness levels, now
313 * taking in consideration the number of interpolated
314 * steps between two levels.
315 */
316 num_levels = (num_input_levels - 1) * num_steps + 1;
317 dev_dbg(dev, "new number of brightness levels: %d\n",
318 num_levels);
319
320 /*
321 * Create a new table of brightness levels with all the
322 * interpolated steps.
323 */
324 table = devm_kcalloc(dev, num_levels, sizeof(*table),
325 GFP_KERNEL);
326 if (!table)
327 return -ENOMEM;
328 /*
329 * Fill the interpolated table[x] = y
330 * by draw lines between each (x1, y1) to (x2, y2).
331 */
332 dx = num_steps;
333 for (i = 0; i < num_input_levels - 1; i++) {
334 x1 = i * dx;
335 x2 = x1 + dx;
336 y1 = data->levels[i];
337 y2 = data->levels[i + 1];
338 dy = (s64)y2 - y1;
339
340 for (x = x1; x < x2; x++) {
341 table[x] = y1 +
342 div_s64(dy * (x - x1), dx);
343 }
344 }
345 /* Fill in the last point, since no line starts here. */
346 table[x2] = y2;
347
348 /*
349 * As we use interpolation lets remove current
350 * brightness levels table and replace for the
351 * new interpolated table.
352 */
353 devm_kfree(dev, data->levels);
354 data->levels = table;
355 }
356
357 data->max_brightness = num_levels - 1;
358 }
359
360 return 0;
361 }
362
363 static const struct of_device_id pwm_backlight_of_match[] = {
364 { .compatible = "pwm-backlight" },
365 { }
366 };
367
368 MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
369 #else
pwm_backlight_parse_dt(struct device * dev,struct platform_pwm_backlight_data * data)370 static int pwm_backlight_parse_dt(struct device *dev,
371 struct platform_pwm_backlight_data *data)
372 {
373 return -ENODEV;
374 }
375
376 static
pwm_backlight_brightness_default(struct device * dev,struct platform_pwm_backlight_data * data,unsigned int period)377 int pwm_backlight_brightness_default(struct device *dev,
378 struct platform_pwm_backlight_data *data,
379 unsigned int period)
380 {
381 return -ENODEV;
382 }
383 #endif
384
pwm_backlight_is_linear(struct platform_pwm_backlight_data * data)385 static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data)
386 {
387 unsigned int nlevels = data->max_brightness + 1;
388 unsigned int min_val = data->levels[0];
389 unsigned int max_val = data->levels[nlevels - 1];
390 /*
391 * Multiplying by 128 means that even in pathological cases such
392 * as (max_val - min_val) == nlevels the error at max_val is less
393 * than 1%.
394 */
395 unsigned int slope = (128 * (max_val - min_val)) / nlevels;
396 unsigned int margin = (max_val - min_val) / 20; /* 5% */
397 int i;
398
399 for (i = 1; i < nlevels; i++) {
400 unsigned int linear_value = min_val + ((i * slope) / 128);
401 unsigned int delta = abs(linear_value - data->levels[i]);
402
403 if (delta > margin)
404 return false;
405 }
406
407 return true;
408 }
409
pwm_backlight_initial_power_state(const struct pwm_bl_data * pb)410 static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
411 {
412 struct device_node *node = pb->dev->of_node;
413 bool active = true;
414
415 /*
416 * If the enable GPIO is present, observable (either as input
417 * or output) and off then the backlight is not currently active.
418 * */
419 if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0)
420 active = false;
421
422 if (pb->power_supply && !regulator_is_enabled(pb->power_supply))
423 active = false;
424
425 if (!pwm_is_enabled(pb->pwm))
426 active = false;
427
428 /*
429 * Synchronize the enable_gpio with the observed state of the
430 * hardware.
431 */
432 if (pb->enable_gpio)
433 gpiod_direction_output(pb->enable_gpio, active);
434
435 /*
436 * Do not change pb->enabled here! pb->enabled essentially
437 * tells us if we own one of the regulator's use counts and
438 * right now we do not.
439 */
440
441 /* Not booted with device tree or no phandle link to the node */
442 if (!node || !node->phandle)
443 return FB_BLANK_UNBLANK;
444
445 /*
446 * If the driver is probed from the device tree and there is a
447 * phandle link pointing to the backlight node, it is safe to
448 * assume that another driver will enable the backlight at the
449 * appropriate time. Therefore, if it is disabled, keep it so.
450 */
451 return active ? FB_BLANK_UNBLANK: FB_BLANK_POWERDOWN;
452 }
453
pwm_backlight_probe(struct platform_device * pdev)454 static int pwm_backlight_probe(struct platform_device *pdev)
455 {
456 struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
457 struct platform_pwm_backlight_data defdata;
458 struct backlight_properties props;
459 struct backlight_device *bl;
460 struct pwm_bl_data *pb;
461 struct pwm_state state;
462 unsigned int i;
463 int ret;
464
465 if (!data) {
466 ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
467 if (ret < 0) {
468 dev_err(&pdev->dev, "failed to find platform data\n");
469 return ret;
470 }
471
472 data = &defdata;
473 }
474
475 if (data->init) {
476 ret = data->init(&pdev->dev);
477 if (ret < 0)
478 return ret;
479 }
480
481 pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
482 if (!pb) {
483 ret = -ENOMEM;
484 goto err_alloc;
485 }
486
487 pb->notify = data->notify;
488 pb->notify_after = data->notify_after;
489 pb->check_fb = data->check_fb;
490 pb->exit = data->exit;
491 pb->dev = &pdev->dev;
492 pb->enabled = false;
493 pb->post_pwm_on_delay = data->post_pwm_on_delay;
494 pb->pwm_off_delay = data->pwm_off_delay;
495
496 pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
497 GPIOD_ASIS);
498 if (IS_ERR(pb->enable_gpio)) {
499 ret = PTR_ERR(pb->enable_gpio);
500 goto err_alloc;
501 }
502
503 pb->power_supply = devm_regulator_get_optional(&pdev->dev, "power");
504 if (IS_ERR(pb->power_supply)) {
505 ret = PTR_ERR(pb->power_supply);
506 if (ret == -ENODEV)
507 pb->power_supply = NULL;
508 else
509 goto err_alloc;
510 }
511
512 pb->pwm = devm_pwm_get(&pdev->dev, NULL);
513 if (IS_ERR(pb->pwm)) {
514 ret = PTR_ERR(pb->pwm);
515 if (ret != -EPROBE_DEFER)
516 dev_err(&pdev->dev, "unable to request PWM\n");
517 goto err_alloc;
518 }
519
520 dev_dbg(&pdev->dev, "got pwm for backlight\n");
521
522 /* Sync up PWM state. */
523 pwm_init_state(pb->pwm, &state);
524
525 /*
526 * The DT case will set the pwm_period_ns field to 0 and store the
527 * period, parsed from the DT, in the PWM device. For the non-DT case,
528 * set the period from platform data if it has not already been set
529 * via the PWM lookup table.
530 */
531 if (!state.period && (data->pwm_period_ns > 0))
532 state.period = data->pwm_period_ns;
533
534 ret = pwm_apply_state(pb->pwm, &state);
535 if (ret) {
536 dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
537 ret);
538 goto err_alloc;
539 }
540
541 memset(&props, 0, sizeof(struct backlight_properties));
542
543 if (data->levels) {
544 pb->levels = data->levels;
545
546 /*
547 * For the DT case, only when brightness levels is defined
548 * data->levels is filled. For the non-DT case, data->levels
549 * can come from platform data, however is not usual.
550 */
551 for (i = 0; i <= data->max_brightness; i++)
552 if (data->levels[i] > pb->scale)
553 pb->scale = data->levels[i];
554
555 if (pwm_backlight_is_linear(data))
556 props.scale = BACKLIGHT_SCALE_LINEAR;
557 else
558 props.scale = BACKLIGHT_SCALE_NON_LINEAR;
559 } else if (!data->max_brightness) {
560 /*
561 * If no brightness levels are provided and max_brightness is
562 * not set, use the default brightness table. For the DT case,
563 * max_brightness is set to 0 when brightness levels is not
564 * specified. For the non-DT case, max_brightness is usually
565 * set to some value.
566 */
567
568 /* Get the PWM period (in nanoseconds) */
569 pwm_get_state(pb->pwm, &state);
570
571 ret = pwm_backlight_brightness_default(&pdev->dev, data,
572 state.period);
573 if (ret < 0) {
574 dev_err(&pdev->dev,
575 "failed to setup default brightness table\n");
576 goto err_alloc;
577 }
578
579 for (i = 0; i <= data->max_brightness; i++) {
580 if (data->levels[i] > pb->scale)
581 pb->scale = data->levels[i];
582
583 pb->levels = data->levels;
584 }
585
586 props.scale = BACKLIGHT_SCALE_NON_LINEAR;
587 } else {
588 /*
589 * That only happens for the non-DT case, where platform data
590 * sets the max_brightness value.
591 */
592 pb->scale = data->max_brightness;
593 }
594
595 pb->lth_brightness = data->lth_brightness * (div_u64(state.period,
596 pb->scale));
597
598 props.type = BACKLIGHT_RAW;
599 props.max_brightness = data->max_brightness;
600 bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
601 &pwm_backlight_ops, &props);
602 if (IS_ERR(bl)) {
603 dev_err(&pdev->dev, "failed to register backlight\n");
604 ret = PTR_ERR(bl);
605 goto err_alloc;
606 }
607
608 if (data->dft_brightness > data->max_brightness) {
609 dev_warn(&pdev->dev,
610 "invalid default brightness level: %u, using %u\n",
611 data->dft_brightness, data->max_brightness);
612 data->dft_brightness = data->max_brightness;
613 }
614
615 bl->props.brightness = data->dft_brightness;
616 bl->props.power = pwm_backlight_initial_power_state(pb);
617 backlight_update_status(bl);
618
619 platform_set_drvdata(pdev, bl);
620 return 0;
621
622 err_alloc:
623 if (data->exit)
624 data->exit(&pdev->dev);
625 return ret;
626 }
627
pwm_backlight_remove(struct platform_device * pdev)628 static int pwm_backlight_remove(struct platform_device *pdev)
629 {
630 struct backlight_device *bl = platform_get_drvdata(pdev);
631 struct pwm_bl_data *pb = bl_get_data(bl);
632
633 backlight_device_unregister(bl);
634 pwm_backlight_power_off(pb);
635
636 if (pb->exit)
637 pb->exit(&pdev->dev);
638
639 return 0;
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
647 pwm_backlight_power_off(pb);
648 }
649
650 #ifdef CONFIG_PM_SLEEP
pwm_backlight_suspend(struct device * dev)651 static int pwm_backlight_suspend(struct device *dev)
652 {
653 struct backlight_device *bl = dev_get_drvdata(dev);
654 struct pwm_bl_data *pb = bl_get_data(bl);
655
656 if (pb->notify)
657 pb->notify(pb->dev, 0);
658
659 pwm_backlight_power_off(pb);
660
661 if (pb->notify_after)
662 pb->notify_after(pb->dev, 0);
663
664 return 0;
665 }
666
pwm_backlight_resume(struct device * dev)667 static int pwm_backlight_resume(struct device *dev)
668 {
669 struct backlight_device *bl = dev_get_drvdata(dev);
670
671 backlight_update_status(bl);
672
673 return 0;
674 }
675 #endif
676
677 static const struct dev_pm_ops pwm_backlight_pm_ops = {
678 #ifdef CONFIG_PM_SLEEP
679 .suspend = pwm_backlight_suspend,
680 .resume = pwm_backlight_resume,
681 .poweroff = pwm_backlight_suspend,
682 .restore = pwm_backlight_resume,
683 #endif
684 };
685
686 static struct platform_driver pwm_backlight_driver = {
687 .driver = {
688 .name = "pwm-backlight",
689 .pm = &pwm_backlight_pm_ops,
690 .of_match_table = of_match_ptr(pwm_backlight_of_match),
691 },
692 .probe = pwm_backlight_probe,
693 .remove = pwm_backlight_remove,
694 .shutdown = pwm_backlight_shutdown,
695 };
696
697 module_platform_driver(pwm_backlight_driver);
698
699 MODULE_DESCRIPTION("PWM based Backlight Driver");
700 MODULE_LICENSE("GPL v2");
701 MODULE_ALIAS("platform:pwm-backlight");
702