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
22struct 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 bool legacy;
32 unsigned int post_pwm_on_delay;
33 unsigned int pwm_off_delay;
34 int (*notify)(struct device *,
35 int brightness);
36 void (*notify_after)(struct device *,
37 int brightness);
38 int (*check_fb)(struct device *, struct fb_info *);
39 void (*exit)(struct device *);
40};
41
42static void pwm_backlight_power_on(struct pwm_bl_data *pb)
43{
44 struct pwm_state state;
45 int err;
46
47 pwm_get_state(pb->pwm, &state);
48 if (pb->enabled)
49 return;
50
51 err = regulator_enable(pb->power_supply);
52 if (err < 0)
53 dev_err(pb->dev, "failed to enable power supply\n");
54
55 state.enabled = true;
56 pwm_apply_state(pb->pwm, &state);
57
58 if (pb->post_pwm_on_delay)
59 msleep(pb->post_pwm_on_delay);
60
61 if (pb->enable_gpio)
62 gpiod_set_value_cansleep(pb->enable_gpio, 1);
63
64 pb->enabled = true;
65}
66
67static void pwm_backlight_power_off(struct pwm_bl_data *pb)
68{
69 struct pwm_state state;
70
71 pwm_get_state(pb->pwm, &state);
72 if (!pb->enabled)
73 return;
74
75 if (pb->enable_gpio)
76 gpiod_set_value_cansleep(pb->enable_gpio, 0);
77
78 if (pb->pwm_off_delay)
79 msleep(pb->pwm_off_delay);
80
81 state.enabled = false;
82 state.duty_cycle = 0;
83 pwm_apply_state(pb->pwm, &state);
84
85 regulator_disable(pb->power_supply);
86 pb->enabled = false;
87}
88
89static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
90{
91 unsigned int lth = pb->lth_brightness;
92 struct pwm_state state;
93 u64 duty_cycle;
94
95 pwm_get_state(pb->pwm, &state);
96
97 if (pb->levels)
98 duty_cycle = pb->levels[brightness];
99 else
100 duty_cycle = brightness;
101
102 duty_cycle *= state.period - lth;
103 do_div(duty_cycle, pb->scale);
104
105 return duty_cycle + lth;
106}
107
108static int pwm_backlight_update_status(struct backlight_device *bl)
109{
110 struct pwm_bl_data *pb = bl_get_data(bl);
111 int brightness = backlight_get_brightness(bl);
112 struct pwm_state state;
113
114 if (pb->notify)
115 brightness = pb->notify(pb->dev, brightness);
116
117 if (brightness > 0) {
118 pwm_get_state(pb->pwm, &state);
119 state.duty_cycle = compute_duty_cycle(pb, brightness);
120 pwm_apply_state(pb->pwm, &state);
121 pwm_backlight_power_on(pb);
122 } else {
123 pwm_backlight_power_off(pb);
124 }
125
126 if (pb->notify_after)
127 pb->notify_after(pb->dev, brightness);
128
129 return 0;
130}
131
132static 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
140static 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 */
164static 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 */
192static
193int 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
229static 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
361static const struct of_device_id pwm_backlight_of_match[] = {
362 { .compatible = "pwm-backlight" },
363 { }
364};
365
366MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
367#else
368static int pwm_backlight_parse_dt(struct device *dev,
369 struct platform_pwm_backlight_data *data)
370{
371 return -ENODEV;
372}
373
374static
375int 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
383static 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
408static 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 (!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 if (pb->enable_gpio)
431 gpiod_direction_output(pb->enable_gpio, active);
432
433 /*
434 * Do not change pb->enabled here! pb->enabled essentially
435 * tells us if we own one of the regulator's use counts and
436 * right now we do not.
437 */
438
439 /* Not booted with device tree or no phandle link to the node */
440 if (!node || !node->phandle)
441 return FB_BLANK_UNBLANK;
442
443 /*
444 * If the driver is probed from the device tree and there is a
445 * phandle link pointing to the backlight node, it is safe to
446 * assume that another driver will enable the backlight at the
447 * appropriate time. Therefore, if it is disabled, keep it so.
448 */
449 return active ? FB_BLANK_UNBLANK: FB_BLANK_POWERDOWN;
450}
451
452static int pwm_backlight_probe(struct platform_device *pdev)
453{
454 struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
455 struct platform_pwm_backlight_data defdata;
456 struct backlight_properties props;
457 struct backlight_device *bl;
458 struct device_node *node = pdev->dev.of_node;
459 struct pwm_bl_data *pb;
460 struct pwm_state state;
461 unsigned int i;
462 int ret;
463
464 if (!data) {
465 ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
466 if (ret < 0) {
467 dev_err(&pdev->dev, "failed to find platform data\n");
468 return ret;
469 }
470
471 data = &defdata;
472 }
473
474 if (data->init) {
475 ret = data->init(&pdev->dev);
476 if (ret < 0)
477 return ret;
478 }
479
480 pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
481 if (!pb) {
482 ret = -ENOMEM;
483 goto err_alloc;
484 }
485
486 pb->notify = data->notify;
487 pb->notify_after = data->notify_after;
488 pb->check_fb = data->check_fb;
489 pb->exit = data->exit;
490 pb->dev = &pdev->dev;
491 pb->enabled = false;
492 pb->post_pwm_on_delay = data->post_pwm_on_delay;
493 pb->pwm_off_delay = data->pwm_off_delay;
494
495 pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
496 GPIOD_ASIS);
497 if (IS_ERR(pb->enable_gpio)) {
498 ret = PTR_ERR(pb->enable_gpio);
499 goto err_alloc;
500 }
501
502 pb->power_supply = devm_regulator_get(&pdev->dev, "power");
503 if (IS_ERR(pb->power_supply)) {
504 ret = PTR_ERR(pb->power_supply);
505 goto err_alloc;
506 }
507
508 pb->pwm = devm_pwm_get(&pdev->dev, NULL);
509 if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) {
510 dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
511 pb->legacy = true;
512 pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
513 }
514
515 if (IS_ERR(pb->pwm)) {
516 ret = PTR_ERR(pb->pwm);
517 if (ret != -EPROBE_DEFER)
518 dev_err(&pdev->dev, "unable to request PWM\n");
519 goto err_alloc;
520 }
521
522 dev_dbg(&pdev->dev, "got pwm for backlight\n");
523
524 /* Sync up PWM state. */
525 pwm_init_state(pb->pwm, &state);
526
527 /*
528 * The DT case will set the pwm_period_ns field to 0 and store the
529 * period, parsed from the DT, in the PWM device. For the non-DT case,
530 * set the period from platform data if it has not already been set
531 * via the PWM lookup table.
532 */
533 if (!state.period && (data->pwm_period_ns > 0))
534 state.period = data->pwm_period_ns;
535
536 ret = pwm_apply_state(pb->pwm, &state);
537 if (ret) {
538 dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
539 ret);
540 goto err_alloc;
541 }
542
543 memset(&props, 0, sizeof(struct backlight_properties));
544
545 if (data->levels) {
546 pb->levels = data->levels;
547
548 /*
549 * For the DT case, only when brightness levels is defined
550 * data->levels is filled. For the non-DT case, data->levels
551 * can come from platform data, however is not usual.
552 */
553 for (i = 0; i <= data->max_brightness; i++)
554 if (data->levels[i] > pb->scale)
555 pb->scale = data->levels[i];
556
557 if (pwm_backlight_is_linear(data))
558 props.scale = BACKLIGHT_SCALE_LINEAR;
559 else
560 props.scale = BACKLIGHT_SCALE_NON_LINEAR;
561 } else if (!data->max_brightness) {
562 /*
563 * If no brightness levels are provided and max_brightness is
564 * not set, use the default brightness table. For the DT case,
565 * max_brightness is set to 0 when brightness levels is not
566 * specified. For the non-DT case, max_brightness is usually
567 * set to some value.
568 */
569
570 /* Get the PWM period (in nanoseconds) */
571 pwm_get_state(pb->pwm, &state);
572
573 ret = pwm_backlight_brightness_default(&pdev->dev, data,
574 state.period);
575 if (ret < 0) {
576 dev_err(&pdev->dev,
577 "failed to setup default brightness table\n");
578 goto err_alloc;
579 }
580
581 for (i = 0; i <= data->max_brightness; i++) {
582 if (data->levels[i] > pb->scale)
583 pb->scale = data->levels[i];
584
585 pb->levels = data->levels;
586 }
587
588 props.scale = BACKLIGHT_SCALE_NON_LINEAR;
589 } else {
590 /*
591 * That only happens for the non-DT case, where platform data
592 * sets the max_brightness value.
593 */
594 pb->scale = data->max_brightness;
595 }
596
597 pb->lth_brightness = data->lth_brightness * (div_u64(state.period,
598 pb->scale));
599
600 props.type = BACKLIGHT_RAW;
601 props.max_brightness = data->max_brightness;
602 bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
603 &pwm_backlight_ops, &props);
604 if (IS_ERR(bl)) {
605 dev_err(&pdev->dev, "failed to register backlight\n");
606 ret = PTR_ERR(bl);
607 if (pb->legacy)
608 pwm_free(pb->pwm);
609 goto err_alloc;
610 }
611
612 if (data->dft_brightness > data->max_brightness) {
613 dev_warn(&pdev->dev,
614 "invalid default brightness level: %u, using %u\n",
615 data->dft_brightness, data->max_brightness);
616 data->dft_brightness = data->max_brightness;
617 }
618
619 bl->props.brightness = data->dft_brightness;
620 bl->props.power = pwm_backlight_initial_power_state(pb);
621 backlight_update_status(bl);
622
623 platform_set_drvdata(pdev, bl);
624 return 0;
625
626err_alloc:
627 if (data->exit)
628 data->exit(&pdev->dev);
629 return ret;
630}
631
632static int pwm_backlight_remove(struct platform_device *pdev)
633{
634 struct backlight_device *bl = platform_get_drvdata(pdev);
635 struct pwm_bl_data *pb = bl_get_data(bl);
636
637 backlight_device_unregister(bl);
638 pwm_backlight_power_off(pb);
639
640 if (pb->exit)
641 pb->exit(&pdev->dev);
642 if (pb->legacy)
643 pwm_free(pb->pwm);
644
645 return 0;
646}
647
648static void pwm_backlight_shutdown(struct platform_device *pdev)
649{
650 struct backlight_device *bl = platform_get_drvdata(pdev);
651 struct pwm_bl_data *pb = bl_get_data(bl);
652
653 pwm_backlight_power_off(pb);
654}
655
656#ifdef CONFIG_PM_SLEEP
657static int pwm_backlight_suspend(struct device *dev)
658{
659 struct backlight_device *bl = dev_get_drvdata(dev);
660 struct pwm_bl_data *pb = bl_get_data(bl);
661
662 if (pb->notify)
663 pb->notify(pb->dev, 0);
664
665 pwm_backlight_power_off(pb);
666
667 if (pb->notify_after)
668 pb->notify_after(pb->dev, 0);
669
670 return 0;
671}
672
673static int pwm_backlight_resume(struct device *dev)
674{
675 struct backlight_device *bl = dev_get_drvdata(dev);
676
677 backlight_update_status(bl);
678
679 return 0;
680}
681#endif
682
683static const struct dev_pm_ops pwm_backlight_pm_ops = {
684#ifdef CONFIG_PM_SLEEP
685 .suspend = pwm_backlight_suspend,
686 .resume = pwm_backlight_resume,
687 .poweroff = pwm_backlight_suspend,
688 .restore = pwm_backlight_resume,
689#endif
690};
691
692static struct platform_driver pwm_backlight_driver = {
693 .driver = {
694 .name = "pwm-backlight",
695 .pm = &pwm_backlight_pm_ops,
696 .of_match_table = of_match_ptr(pwm_backlight_of_match),
697 },
698 .probe = pwm_backlight_probe,
699 .remove = pwm_backlight_remove,
700 .shutdown = pwm_backlight_shutdown,
701};
702
703module_platform_driver(pwm_backlight_driver);
704
705MODULE_DESCRIPTION("PWM based Backlight Driver");
706MODULE_LICENSE("GPL v2");
707MODULE_ALIAS("platform:pwm-backlight");
708

source code of linux/drivers/video/backlight/pwm_bl.c