2 * linux/drivers/video/backlight/pwm_bl.c
4 * simple PWM based backlight control, board code has to setup
5 * 1) pin configuration so PWM waveforms can output
6 * 2) platform_data being correctly configured
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2 as
10 * published by the Free Software Foundation.
13 #include <linux/delay.h>
14 #include <linux/gpio/consumer.h>
15 #include <linux/gpio.h>
16 #include <linux/module.h>
17 #include <linux/kernel.h>
18 #include <linux/init.h>
19 #include <linux/platform_device.h>
21 #include <linux/backlight.h>
22 #include <linux/err.h>
23 #include <linux/pwm.h>
24 #include <linux/pwm_backlight.h>
25 #include <linux/regulator/consumer.h>
26 #include <linux/slab.h>
29 struct pwm_device *pwm;
31 unsigned int lth_brightness;
34 struct regulator *power_supply;
35 struct gpio_desc *enable_gpio;
38 unsigned int post_pwm_on_delay;
39 unsigned int pwm_off_delay;
40 int (*notify)(struct device *,
42 void (*notify_after)(struct device *,
44 int (*check_fb)(struct device *, struct fb_info *);
45 void (*exit)(struct device *);
48 static void pwm_backlight_power_on(struct pwm_bl_data *pb)
50 struct pwm_state state;
53 pwm_get_state(pb->pwm, &state);
57 err = regulator_enable(pb->power_supply);
59 dev_err(pb->dev, "failed to enable power supply\n");
62 pwm_apply_state(pb->pwm, &state);
64 if (pb->post_pwm_on_delay)
65 msleep(pb->post_pwm_on_delay);
68 gpiod_set_value_cansleep(pb->enable_gpio, 1);
73 static void pwm_backlight_power_off(struct pwm_bl_data *pb)
75 struct pwm_state state;
77 pwm_get_state(pb->pwm, &state);
82 gpiod_set_value_cansleep(pb->enable_gpio, 0);
84 if (pb->pwm_off_delay)
85 msleep(pb->pwm_off_delay);
87 state.enabled = false;
89 pwm_apply_state(pb->pwm, &state);
91 regulator_disable(pb->power_supply);
95 static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
97 unsigned int lth = pb->lth_brightness;
98 struct pwm_state state;
101 pwm_get_state(pb->pwm, &state);
104 duty_cycle = pb->levels[brightness];
106 duty_cycle = brightness;
108 duty_cycle *= state.period - lth;
109 do_div(duty_cycle, pb->scale);
111 return duty_cycle + lth;
114 static int pwm_backlight_update_status(struct backlight_device *bl)
116 struct pwm_bl_data *pb = bl_get_data(bl);
117 int brightness = bl->props.brightness;
118 struct pwm_state state;
120 if (bl->props.power != FB_BLANK_UNBLANK ||
121 bl->props.fb_blank != FB_BLANK_UNBLANK ||
122 bl->props.state & BL_CORE_FBBLANK)
126 brightness = pb->notify(pb->dev, brightness);
128 if (brightness > 0) {
129 pwm_get_state(pb->pwm, &state);
130 state.duty_cycle = compute_duty_cycle(pb, brightness);
131 pwm_apply_state(pb->pwm, &state);
132 pwm_backlight_power_on(pb);
134 pwm_backlight_power_off(pb);
136 if (pb->notify_after)
137 pb->notify_after(pb->dev, brightness);
142 static int pwm_backlight_check_fb(struct backlight_device *bl,
143 struct fb_info *info)
145 struct pwm_bl_data *pb = bl_get_data(bl);
147 return !pb->check_fb || pb->check_fb(pb->dev, info);
150 static const struct backlight_ops pwm_backlight_ops = {
151 .update_status = pwm_backlight_update_status,
152 .check_fb = pwm_backlight_check_fb,
156 #define PWM_LUMINANCE_SCALE 10000 /* luminance scale */
158 /* An integer based power function */
159 static u64 int_pow(u64 base, int exp)
174 * CIE lightness to PWM conversion.
176 * The CIE 1931 lightness formula is what actually describes how we perceive
178 * Y = (L* / 902.3) if L* ≤ 0.08856
179 * Y = ((L* + 16) / 116)^3 if L* > 0.08856
181 * Where Y is the luminance, the amount of light coming out of the screen, and
182 * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
183 * perceives the screen to be, and is a number between 0 and 100.
185 * The following function does the fixed point maths needed to implement the
188 static u64 cie1931(unsigned int lightness, unsigned int scale)
193 if (lightness <= (8 * scale)) {
194 retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023);
196 retval = int_pow((lightness + (16 * scale)) / 116, 3);
197 retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
204 * Create a default correction table for PWM values to create linear brightness
205 * for LED based backlights using the CIE1931 algorithm.
208 int pwm_backlight_brightness_default(struct device *dev,
209 struct platform_pwm_backlight_data *data,
212 unsigned int counter = 0;
217 * Count the number of bits needed to represent the period number. The
218 * number of bits is used to calculate the number of levels used for the
219 * brightness-levels table, the purpose of this calculation is have a
220 * pre-computed table with enough levels to get linear brightness
221 * perception. The period is divided by the number of bits so for a
222 * 8-bit PWM we have 255 / 8 = 32 brightness levels or for a 16-bit PWM
223 * we have 65535 / 16 = 4096 brightness levels.
225 * Note that this method is based on empirical testing on different
226 * devices with PWM of 8 and 16 bits of resolution.
234 data->max_brightness = DIV_ROUND_UP(period, counter);
235 data->levels = devm_kcalloc(dev, data->max_brightness,
236 sizeof(*data->levels), GFP_KERNEL);
240 /* Fill the table using the cie1931 algorithm */
241 for (i = 0; i < data->max_brightness; i++) {
242 retval = cie1931((i * PWM_LUMINANCE_SCALE) /
243 data->max_brightness, PWM_LUMINANCE_SCALE) *
245 retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
246 if (retval > UINT_MAX)
248 data->levels[i] = (unsigned int)retval;
251 data->dft_brightness = data->max_brightness / 2;
252 data->max_brightness--;
257 static int pwm_backlight_parse_dt(struct device *dev,
258 struct platform_pwm_backlight_data *data)
260 struct device_node *node = dev->of_node;
261 unsigned int num_levels = 0;
262 unsigned int levels_count;
263 unsigned int num_steps = 0;
264 struct property *prop;
273 memset(data, 0, sizeof(*data));
276 * These values are optional and set as 0 by default, the out values
277 * are modified only if a valid u32 value can be decoded.
279 of_property_read_u32(node, "post-pwm-on-delay-ms",
280 &data->post_pwm_on_delay);
281 of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay);
283 data->enable_gpio = -EINVAL;
286 * Determine the number of brightness levels, if this property is not
287 * set a default table of brightness levels will be used.
289 prop = of_find_property(node, "brightness-levels", &length);
293 data->max_brightness = length / sizeof(u32);
295 /* read brightness levels from DT property */
296 if (data->max_brightness > 0) {
297 size_t size = sizeof(*data->levels) * data->max_brightness;
298 unsigned int i, j, n = 0;
300 data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
304 ret = of_property_read_u32_array(node, "brightness-levels",
306 data->max_brightness);
310 ret = of_property_read_u32(node, "default-brightness-level",
315 data->dft_brightness = value;
318 * This property is optional, if is set enables linear
319 * interpolation between each of the values of brightness levels
320 * and creates a new pre-computed table.
322 of_property_read_u32(node, "num-interpolated-steps",
326 * Make sure that there is at least two entries in the
327 * brightness-levels table, otherwise we can't interpolate
328 * between two points.
331 if (data->max_brightness < 2) {
332 dev_err(dev, "can't interpolate\n");
337 * Recalculate the number of brightness levels, now
338 * taking in consideration the number of interpolated
339 * steps between two levels.
341 for (i = 0; i < data->max_brightness - 1; i++) {
342 if ((data->levels[i + 1] - data->levels[i]) /
344 num_levels += num_steps;
349 dev_dbg(dev, "new number of brightness levels: %d\n",
353 * Create a new table of brightness levels with all the
354 * interpolated steps.
356 size = sizeof(*table) * num_levels;
357 table = devm_kzalloc(dev, size, GFP_KERNEL);
361 /* Fill the interpolated table. */
363 for (i = 0; i < data->max_brightness - 1; i++) {
364 value = data->levels[i];
365 n = (data->levels[i + 1] - value) / num_steps;
367 for (j = 0; j < num_steps; j++) {
368 table[levels_count] = value;
373 table[levels_count] = data->levels[i];
377 table[levels_count] = data->levels[i];
380 * As we use interpolation lets remove current
381 * brightness levels table and replace for the
382 * new interpolated table.
384 devm_kfree(dev, data->levels);
385 data->levels = table;
388 * Reassign max_brightness value to the new total number
389 * of brightness levels.
391 data->max_brightness = num_levels;
394 data->max_brightness--;
400 static const struct of_device_id pwm_backlight_of_match[] = {
401 { .compatible = "pwm-backlight" },
405 MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
407 static int pwm_backlight_parse_dt(struct device *dev,
408 struct platform_pwm_backlight_data *data)
414 int pwm_backlight_brightness_default(struct device *dev,
415 struct platform_pwm_backlight_data *data,
422 static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
424 struct device_node *node = pb->dev->of_node;
426 /* Not booted with device tree or no phandle link to the node */
427 if (!node || !node->phandle)
428 return FB_BLANK_UNBLANK;
431 * If the driver is probed from the device tree and there is a
432 * phandle link pointing to the backlight node, it is safe to
433 * assume that another driver will enable the backlight at the
434 * appropriate time. Therefore, if it is disabled, keep it so.
437 /* if the enable GPIO is disabled, do not enable the backlight */
438 if (pb->enable_gpio && gpiod_get_value(pb->enable_gpio) == 0)
439 return FB_BLANK_POWERDOWN;
441 /* The regulator is disabled, do not enable the backlight */
442 if (!regulator_is_enabled(pb->power_supply))
443 return FB_BLANK_POWERDOWN;
445 /* The PWM is disabled, keep it like this */
446 if (!pwm_is_enabled(pb->pwm))
447 return FB_BLANK_POWERDOWN;
449 return FB_BLANK_UNBLANK;
452 static int pwm_backlight_probe(struct platform_device *pdev)
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;
465 ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
467 dev_err(&pdev->dev, "failed to find platform data\n");
475 ret = data->init(&pdev->dev);
480 pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
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;
492 pb->post_pwm_on_delay = data->post_pwm_on_delay;
493 pb->pwm_off_delay = data->pwm_off_delay;
495 pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
497 if (IS_ERR(pb->enable_gpio)) {
498 ret = PTR_ERR(pb->enable_gpio);
503 * Compatibility fallback for drivers still using the integer GPIO
504 * platform data. Must go away soon.
506 if (!pb->enable_gpio && gpio_is_valid(data->enable_gpio)) {
507 ret = devm_gpio_request_one(&pdev->dev, data->enable_gpio,
508 GPIOF_OUT_INIT_HIGH, "enable");
510 dev_err(&pdev->dev, "failed to request GPIO#%d: %d\n",
511 data->enable_gpio, ret);
515 pb->enable_gpio = gpio_to_desc(data->enable_gpio);
519 * If the GPIO is not known to be already configured as output, that
520 * is, if gpiod_get_direction returns either 1 or -EINVAL, change the
521 * direction to output and set the GPIO as active.
522 * Do not force the GPIO to active when it was already output as it
523 * could cause backlight flickering or we would enable the backlight too
524 * early. Leave the decision of the initial backlight state for later.
526 if (pb->enable_gpio &&
527 gpiod_get_direction(pb->enable_gpio) != 0)
528 gpiod_direction_output(pb->enable_gpio, 1);
530 pb->power_supply = devm_regulator_get(&pdev->dev, "power");
531 if (IS_ERR(pb->power_supply)) {
532 ret = PTR_ERR(pb->power_supply);
536 pb->pwm = devm_pwm_get(&pdev->dev, NULL);
537 if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) {
538 dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
540 pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
543 if (IS_ERR(pb->pwm)) {
544 ret = PTR_ERR(pb->pwm);
545 if (ret != -EPROBE_DEFER)
546 dev_err(&pdev->dev, "unable to request PWM\n");
550 dev_dbg(&pdev->dev, "got pwm for backlight\n");
552 /* Sync up PWM state. */
553 pwm_init_state(pb->pwm, &state);
556 * The DT case will set the pwm_period_ns field to 0 and store the
557 * period, parsed from the DT, in the PWM device. For the non-DT case,
558 * set the period from platform data if it has not already been set
559 * via the PWM lookup table.
561 if (!state.period && (data->pwm_period_ns > 0))
562 state.period = data->pwm_period_ns;
564 ret = pwm_apply_state(pb->pwm, &state);
566 dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
573 * For the DT case, only when brightness levels is defined
574 * data->levels is filled. For the non-DT case, data->levels
575 * can come from platform data, however is not usual.
577 for (i = 0; i <= data->max_brightness; i++) {
578 if (data->levels[i] > pb->scale)
579 pb->scale = data->levels[i];
581 pb->levels = data->levels;
583 } else if (!data->max_brightness) {
585 * If no brightness levels are provided and max_brightness is
586 * not set, use the default brightness table. For the DT case,
587 * max_brightness is set to 0 when brightness levels is not
588 * specified. For the non-DT case, max_brightness is usually
592 /* Get the PWM period (in nanoseconds) */
593 pwm_get_state(pb->pwm, &state);
595 ret = pwm_backlight_brightness_default(&pdev->dev, data,
599 "failed to setup default brightness table\n");
603 for (i = 0; i <= data->max_brightness; i++) {
604 if (data->levels[i] > pb->scale)
605 pb->scale = data->levels[i];
607 pb->levels = data->levels;
611 * That only happens for the non-DT case, where platform data
612 * sets the max_brightness value.
614 pb->scale = data->max_brightness;
617 pb->lth_brightness = data->lth_brightness * (state.period / pb->scale);
619 memset(&props, 0, sizeof(struct backlight_properties));
620 props.type = BACKLIGHT_RAW;
621 props.max_brightness = data->max_brightness;
622 bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
623 &pwm_backlight_ops, &props);
625 dev_err(&pdev->dev, "failed to register backlight\n");
632 if (data->dft_brightness > data->max_brightness) {
634 "invalid default brightness level: %u, using %u\n",
635 data->dft_brightness, data->max_brightness);
636 data->dft_brightness = data->max_brightness;
639 bl->props.brightness = data->dft_brightness;
640 bl->props.power = pwm_backlight_initial_power_state(pb);
641 backlight_update_status(bl);
643 platform_set_drvdata(pdev, bl);
648 data->exit(&pdev->dev);
652 static int pwm_backlight_remove(struct platform_device *pdev)
654 struct backlight_device *bl = platform_get_drvdata(pdev);
655 struct pwm_bl_data *pb = bl_get_data(bl);
657 backlight_device_unregister(bl);
658 pwm_backlight_power_off(pb);
661 pb->exit(&pdev->dev);
668 static void pwm_backlight_shutdown(struct platform_device *pdev)
670 struct backlight_device *bl = platform_get_drvdata(pdev);
671 struct pwm_bl_data *pb = bl_get_data(bl);
673 pwm_backlight_power_off(pb);
676 #ifdef CONFIG_PM_SLEEP
677 static int pwm_backlight_suspend(struct device *dev)
679 struct backlight_device *bl = dev_get_drvdata(dev);
680 struct pwm_bl_data *pb = bl_get_data(bl);
683 pb->notify(pb->dev, 0);
685 pwm_backlight_power_off(pb);
687 if (pb->notify_after)
688 pb->notify_after(pb->dev, 0);
693 static int pwm_backlight_resume(struct device *dev)
695 struct backlight_device *bl = dev_get_drvdata(dev);
697 backlight_update_status(bl);
703 static const struct dev_pm_ops pwm_backlight_pm_ops = {
704 #ifdef CONFIG_PM_SLEEP
705 .suspend = pwm_backlight_suspend,
706 .resume = pwm_backlight_resume,
707 .poweroff = pwm_backlight_suspend,
708 .restore = pwm_backlight_resume,
712 static struct platform_driver pwm_backlight_driver = {
714 .name = "pwm-backlight",
715 .pm = &pwm_backlight_pm_ops,
716 .of_match_table = of_match_ptr(pwm_backlight_of_match),
718 .probe = pwm_backlight_probe,
719 .remove = pwm_backlight_remove,
720 .shutdown = pwm_backlight_shutdown,
723 module_platform_driver(pwm_backlight_driver);
725 MODULE_DESCRIPTION("PWM based Backlight Driver");
726 MODULE_LICENSE("GPL");
727 MODULE_ALIAS("platform:pwm-backlight");