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 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
pwm_backlight_power_on(struct pwm_bl_data * pb)42 static 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
pwm_backlight_power_off(struct pwm_bl_data * pb)67 static 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
compute_duty_cycle(struct pwm_bl_data * pb,int brightness)89 static 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
pwm_backlight_update_status(struct backlight_device * bl)108 static 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
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 size_t size = sizeof(*data->levels) * num_levels;
267
268 data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
269 if (!data->levels)
270 return -ENOMEM;
271
272 ret = of_property_read_u32_array(node, "brightness-levels",
273 data->levels,
274 num_levels);
275 if (ret < 0)
276 return ret;
277
278 ret = of_property_read_u32(node, "default-brightness-level",
279 &value);
280 if (ret < 0)
281 return ret;
282
283 data->dft_brightness = value;
284
285 /*
286 * This property is optional, if is set enables linear
287 * interpolation between each of the values of brightness levels
288 * and creates a new pre-computed table.
289 */
290 of_property_read_u32(node, "num-interpolated-steps",
291 &num_steps);
292
293 /*
294 * Make sure that there is at least two entries in the
295 * brightness-levels table, otherwise we can't interpolate
296 * between two points.
297 */
298 if (num_steps) {
299 unsigned int num_input_levels = num_levels;
300 unsigned int i;
301 u32 x1, x2, x, dx;
302 u32 y1, y2;
303 s64 dy;
304
305 if (num_input_levels < 2) {
306 dev_err(dev, "can't interpolate\n");
307 return -EINVAL;
308 }
309
310 /*
311 * Recalculate the number of brightness levels, now
312 * taking in consideration the number of interpolated
313 * steps between two levels.
314 */
315 num_levels = (num_input_levels - 1) * num_steps + 1;
316 dev_dbg(dev, "new number of brightness levels: %d\n",
317 num_levels);
318
319 /*
320 * Create a new table of brightness levels with all the
321 * interpolated steps.
322 */
323 size = sizeof(*table) * num_levels;
324 table = devm_kzalloc(dev, size, GFP_KERNEL);
325 if (!table)
326 return -ENOMEM;
327 /*
328 * Fill the interpolated table[x] = y
329 * by draw lines between each (x1, y1) to (x2, y2).
330 */
331 dx = num_steps;
332 for (i = 0; i < num_input_levels - 1; i++) {
333 x1 = i * dx;
334 x2 = x1 + dx;
335 y1 = data->levels[i];
336 y2 = data->levels[i + 1];
337 dy = (s64)y2 - y1;
338
339 for (x = x1; x < x2; x++) {
340 table[x] = y1 +
341 div_s64(dy * (x - x1), dx);
342 }
343 }
344 /* Fill in the last point, since no line starts here. */
345 table[x2] = y2;
346
347 /*
348 * As we use interpolation lets remove current
349 * brightness levels table and replace for the
350 * new interpolated table.
351 */
352 devm_kfree(dev, data->levels);
353 data->levels = table;
354 }
355
356 data->max_brightness = num_levels - 1;
357 }
358
359 return 0;
360 }
361
362 static const struct of_device_id pwm_backlight_of_match[] = {
363 { .compatible = "pwm-backlight" },
364 { }
365 };
366
367 MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
368 #else
pwm_backlight_parse_dt(struct device * dev,struct platform_pwm_backlight_data * data)369 static int pwm_backlight_parse_dt(struct device *dev,
370 struct platform_pwm_backlight_data *data)
371 {
372 return -ENODEV;
373 }
374
375 static
pwm_backlight_brightness_default(struct device * dev,struct platform_pwm_backlight_data * data,unsigned int period)376 int pwm_backlight_brightness_default(struct device *dev,
377 struct platform_pwm_backlight_data *data,
378 unsigned int period)
379 {
380 return -ENODEV;
381 }
382 #endif
383
pwm_backlight_is_linear(struct platform_pwm_backlight_data * data)384 static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data)
385 {
386 unsigned int nlevels = data->max_brightness + 1;
387 unsigned int min_val = data->levels[0];
388 unsigned int max_val = data->levels[nlevels - 1];
389 /*
390 * Multiplying by 128 means that even in pathological cases such
391 * as (max_val - min_val) == nlevels the error at max_val is less
392 * than 1%.
393 */
394 unsigned int slope = (128 * (max_val - min_val)) / nlevels;
395 unsigned int margin = (max_val - min_val) / 20; /* 5% */
396 int i;
397
398 for (i = 1; i < nlevels; i++) {
399 unsigned int linear_value = min_val + ((i * slope) / 128);
400 unsigned int delta = abs(linear_value - data->levels[i]);
401
402 if (delta > margin)
403 return false;
404 }
405
406 return true;
407 }
408
pwm_backlight_initial_power_state(const struct pwm_bl_data * pb)409 static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
410 {
411 struct device_node *node = pb->dev->of_node;
412 bool active = true;
413
414 /*
415 * If the enable GPIO is present, observable (either as input
416 * or output) and off then the backlight is not currently active.
417 * */
418 if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0)
419 active = false;
420
421 if (!regulator_is_enabled(pb->power_supply))
422 active = false;
423
424 if (!pwm_is_enabled(pb->pwm))
425 active = false;
426
427 /*
428 * Synchronize the enable_gpio with the observed state of the
429 * hardware.
430 */
431 if (pb->enable_gpio)
432 gpiod_direction_output(pb->enable_gpio, active);
433
434 /*
435 * Do not change pb->enabled here! pb->enabled essentially
436 * tells us if we own one of the regulator's use counts and
437 * right now we do not.
438 */
439
440 /* Not booted with device tree or no phandle link to the node */
441 if (!node || !node->phandle)
442 return FB_BLANK_UNBLANK;
443
444 /*
445 * If the driver is probed from the device tree and there is a
446 * phandle link pointing to the backlight node, it is safe to
447 * assume that another driver will enable the backlight at the
448 * appropriate time. Therefore, if it is disabled, keep it so.
449 */
450 return active ? FB_BLANK_UNBLANK: FB_BLANK_POWERDOWN;
451 }
452
pwm_backlight_probe(struct platform_device * pdev)453 static int pwm_backlight_probe(struct platform_device *pdev)
454 {
455 struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
456 struct platform_pwm_backlight_data defdata;
457 struct backlight_properties props;
458 struct backlight_device *bl;
459 struct device_node *node = pdev->dev.of_node;
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(&pdev->dev, "power");
504 if (IS_ERR(pb->power_supply)) {
505 ret = PTR_ERR(pb->power_supply);
506 goto err_alloc;
507 }
508
509 pb->pwm = devm_pwm_get(&pdev->dev, NULL);
510 if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) {
511 dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
512 pb->legacy = true;
513 pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
514 }
515
516 if (IS_ERR(pb->pwm)) {
517 ret = PTR_ERR(pb->pwm);
518 if (ret != -EPROBE_DEFER)
519 dev_err(&pdev->dev, "unable to request PWM\n");
520 goto err_alloc;
521 }
522
523 dev_dbg(&pdev->dev, "got pwm for backlight\n");
524
525 /* Sync up PWM state. */
526 pwm_init_state(pb->pwm, &state);
527
528 /*
529 * The DT case will set the pwm_period_ns field to 0 and store the
530 * period, parsed from the DT, in the PWM device. For the non-DT case,
531 * set the period from platform data if it has not already been set
532 * via the PWM lookup table.
533 */
534 if (!state.period && (data->pwm_period_ns > 0))
535 state.period = data->pwm_period_ns;
536
537 ret = pwm_apply_state(pb->pwm, &state);
538 if (ret) {
539 dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
540 ret);
541 goto err_alloc;
542 }
543
544 memset(&props, 0, sizeof(struct backlight_properties));
545
546 if (data->levels) {
547 pb->levels = data->levels;
548
549 /*
550 * For the DT case, only when brightness levels is defined
551 * data->levels is filled. For the non-DT case, data->levels
552 * can come from platform data, however is not usual.
553 */
554 for (i = 0; i <= data->max_brightness; i++)
555 if (data->levels[i] > pb->scale)
556 pb->scale = data->levels[i];
557
558 if (pwm_backlight_is_linear(data))
559 props.scale = BACKLIGHT_SCALE_LINEAR;
560 else
561 props.scale = BACKLIGHT_SCALE_NON_LINEAR;
562 } else if (!data->max_brightness) {
563 /*
564 * If no brightness levels are provided and max_brightness is
565 * not set, use the default brightness table. For the DT case,
566 * max_brightness is set to 0 when brightness levels is not
567 * specified. For the non-DT case, max_brightness is usually
568 * set to some value.
569 */
570
571 /* Get the PWM period (in nanoseconds) */
572 pwm_get_state(pb->pwm, &state);
573
574 ret = pwm_backlight_brightness_default(&pdev->dev, data,
575 state.period);
576 if (ret < 0) {
577 dev_err(&pdev->dev,
578 "failed to setup default brightness table\n");
579 goto err_alloc;
580 }
581
582 for (i = 0; i <= data->max_brightness; i++) {
583 if (data->levels[i] > pb->scale)
584 pb->scale = data->levels[i];
585
586 pb->levels = data->levels;
587 }
588
589 props.scale = BACKLIGHT_SCALE_NON_LINEAR;
590 } else {
591 /*
592 * That only happens for the non-DT case, where platform data
593 * sets the max_brightness value.
594 */
595 pb->scale = data->max_brightness;
596 }
597
598 pb->lth_brightness = data->lth_brightness * (div_u64(state.period,
599 pb->scale));
600
601 props.type = BACKLIGHT_RAW;
602 props.max_brightness = data->max_brightness;
603 bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
604 &pwm_backlight_ops, &props);
605 if (IS_ERR(bl)) {
606 dev_err(&pdev->dev, "failed to register backlight\n");
607 ret = PTR_ERR(bl);
608 if (pb->legacy)
609 pwm_free(pb->pwm);
610 goto err_alloc;
611 }
612
613 if (data->dft_brightness > data->max_brightness) {
614 dev_warn(&pdev->dev,
615 "invalid default brightness level: %u, using %u\n",
616 data->dft_brightness, data->max_brightness);
617 data->dft_brightness = data->max_brightness;
618 }
619
620 bl->props.brightness = data->dft_brightness;
621 bl->props.power = pwm_backlight_initial_power_state(pb);
622 backlight_update_status(bl);
623
624 platform_set_drvdata(pdev, bl);
625 return 0;
626
627 err_alloc:
628 if (data->exit)
629 data->exit(&pdev->dev);
630 return ret;
631 }
632
pwm_backlight_remove(struct platform_device * pdev)633 static int pwm_backlight_remove(struct platform_device *pdev)
634 {
635 struct backlight_device *bl = platform_get_drvdata(pdev);
636 struct pwm_bl_data *pb = bl_get_data(bl);
637
638 backlight_device_unregister(bl);
639 pwm_backlight_power_off(pb);
640
641 if (pb->exit)
642 pb->exit(&pdev->dev);
643 if (pb->legacy)
644 pwm_free(pb->pwm);
645
646 return 0;
647 }
648
pwm_backlight_shutdown(struct platform_device * pdev)649 static void pwm_backlight_shutdown(struct platform_device *pdev)
650 {
651 struct backlight_device *bl = platform_get_drvdata(pdev);
652 struct pwm_bl_data *pb = bl_get_data(bl);
653
654 pwm_backlight_power_off(pb);
655 }
656
657 #ifdef CONFIG_PM_SLEEP
pwm_backlight_suspend(struct device * dev)658 static int pwm_backlight_suspend(struct device *dev)
659 {
660 struct backlight_device *bl = dev_get_drvdata(dev);
661 struct pwm_bl_data *pb = bl_get_data(bl);
662
663 if (pb->notify)
664 pb->notify(pb->dev, 0);
665
666 pwm_backlight_power_off(pb);
667
668 if (pb->notify_after)
669 pb->notify_after(pb->dev, 0);
670
671 return 0;
672 }
673
pwm_backlight_resume(struct device * dev)674 static int pwm_backlight_resume(struct device *dev)
675 {
676 struct backlight_device *bl = dev_get_drvdata(dev);
677
678 backlight_update_status(bl);
679
680 return 0;
681 }
682 #endif
683
684 static const struct dev_pm_ops pwm_backlight_pm_ops = {
685 #ifdef CONFIG_PM_SLEEP
686 .suspend = pwm_backlight_suspend,
687 .resume = pwm_backlight_resume,
688 .poweroff = pwm_backlight_suspend,
689 .restore = pwm_backlight_resume,
690 #endif
691 };
692
693 static struct platform_driver pwm_backlight_driver = {
694 .driver = {
695 .name = "pwm-backlight",
696 .pm = &pwm_backlight_pm_ops,
697 .of_match_table = of_match_ptr(pwm_backlight_of_match),
698 },
699 .probe = pwm_backlight_probe,
700 .remove = pwm_backlight_remove,
701 .shutdown = pwm_backlight_shutdown,
702 };
703
704 module_platform_driver(pwm_backlight_driver);
705
706 MODULE_DESCRIPTION("PWM based Backlight Driver");
707 MODULE_LICENSE("GPL v2");
708 MODULE_ALIAS("platform:pwm-backlight");
709