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706 lines
18 KiB
706 lines
18 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Simple PWM based backlight control, board code has to setup |
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* 1) pin configuration so PWM waveforms can output |
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* 2) platform_data being correctly configured |
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*/ |
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|
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#include <linux/delay.h> |
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#include <linux/gpio/consumer.h> |
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#include <linux/module.h> |
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#include <linux/kernel.h> |
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#include <linux/init.h> |
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#include <linux/platform_device.h> |
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#include <linux/fb.h> |
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#include <linux/backlight.h> |
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#include <linux/err.h> |
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#include <linux/pwm.h> |
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#include <linux/pwm_backlight.h> |
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#include <linux/regulator/consumer.h> |
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#include <linux/slab.h> |
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struct pwm_bl_data { |
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struct pwm_device *pwm; |
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struct device *dev; |
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unsigned int lth_brightness; |
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unsigned int *levels; |
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bool enabled; |
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struct regulator *power_supply; |
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struct gpio_desc *enable_gpio; |
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unsigned int scale; |
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bool legacy; |
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unsigned int post_pwm_on_delay; |
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unsigned int pwm_off_delay; |
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int (*notify)(struct device *, |
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int brightness); |
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void (*notify_after)(struct device *, |
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int brightness); |
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int (*check_fb)(struct device *, struct fb_info *); |
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void (*exit)(struct device *); |
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}; |
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static void pwm_backlight_power_on(struct pwm_bl_data *pb) |
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{ |
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struct pwm_state state; |
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int err; |
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pwm_get_state(pb->pwm, &state); |
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if (pb->enabled) |
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return; |
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err = regulator_enable(pb->power_supply); |
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if (err < 0) |
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dev_err(pb->dev, "failed to enable power supply\n"); |
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state.enabled = true; |
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pwm_apply_state(pb->pwm, &state); |
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if (pb->post_pwm_on_delay) |
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msleep(pb->post_pwm_on_delay); |
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if (pb->enable_gpio) |
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gpiod_set_value_cansleep(pb->enable_gpio, 1); |
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pb->enabled = true; |
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} |
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static void pwm_backlight_power_off(struct pwm_bl_data *pb) |
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{ |
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struct pwm_state state; |
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pwm_get_state(pb->pwm, &state); |
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if (!pb->enabled) |
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return; |
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if (pb->enable_gpio) |
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gpiod_set_value_cansleep(pb->enable_gpio, 0); |
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if (pb->pwm_off_delay) |
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msleep(pb->pwm_off_delay); |
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state.enabled = false; |
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state.duty_cycle = 0; |
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pwm_apply_state(pb->pwm, &state); |
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regulator_disable(pb->power_supply); |
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pb->enabled = false; |
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} |
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static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness) |
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{ |
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unsigned int lth = pb->lth_brightness; |
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struct pwm_state state; |
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u64 duty_cycle; |
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pwm_get_state(pb->pwm, &state); |
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if (pb->levels) |
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duty_cycle = pb->levels[brightness]; |
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else |
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duty_cycle = brightness; |
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duty_cycle *= state.period - lth; |
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do_div(duty_cycle, pb->scale); |
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return duty_cycle + lth; |
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} |
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static int pwm_backlight_update_status(struct backlight_device *bl) |
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{ |
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struct pwm_bl_data *pb = bl_get_data(bl); |
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int brightness = backlight_get_brightness(bl); |
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struct pwm_state state; |
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if (pb->notify) |
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brightness = pb->notify(pb->dev, brightness); |
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|
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if (brightness > 0) { |
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pwm_get_state(pb->pwm, &state); |
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state.duty_cycle = compute_duty_cycle(pb, brightness); |
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pwm_apply_state(pb->pwm, &state); |
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pwm_backlight_power_on(pb); |
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} else { |
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pwm_backlight_power_off(pb); |
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} |
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if (pb->notify_after) |
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pb->notify_after(pb->dev, brightness); |
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return 0; |
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} |
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static int pwm_backlight_check_fb(struct backlight_device *bl, |
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struct fb_info *info) |
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{ |
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struct pwm_bl_data *pb = bl_get_data(bl); |
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return !pb->check_fb || pb->check_fb(pb->dev, info); |
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} |
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static const struct backlight_ops pwm_backlight_ops = { |
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.update_status = pwm_backlight_update_status, |
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.check_fb = pwm_backlight_check_fb, |
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}; |
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#ifdef CONFIG_OF |
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#define PWM_LUMINANCE_SHIFT 16 |
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#define PWM_LUMINANCE_SCALE (1 << PWM_LUMINANCE_SHIFT) /* luminance scale */ |
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/* |
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* CIE lightness to PWM conversion. |
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* |
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* The CIE 1931 lightness formula is what actually describes how we perceive |
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* light: |
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* Y = (L* / 903.3) if L* ≤ 8 |
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* Y = ((L* + 16) / 116)^3 if L* > 8 |
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* |
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* Where Y is the luminance, the amount of light coming out of the screen, and |
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* is a number between 0.0 and 1.0; and L* is the lightness, how bright a human |
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* perceives the screen to be, and is a number between 0 and 100. |
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* |
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* The following function does the fixed point maths needed to implement the |
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* above formula. |
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*/ |
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static u64 cie1931(unsigned int lightness) |
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{ |
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u64 retval; |
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/* |
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* @lightness is given as a number between 0 and 1, expressed |
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* as a fixed-point number in scale |
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* PWM_LUMINANCE_SCALE. Convert to a percentage, still |
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* expressed as a fixed-point number, so the above formulas |
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* can be applied. |
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*/ |
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lightness *= 100; |
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if (lightness <= (8 * PWM_LUMINANCE_SCALE)) { |
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retval = DIV_ROUND_CLOSEST(lightness * 10, 9033); |
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} else { |
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retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116; |
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retval *= retval * retval; |
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retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1); |
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retval >>= 2*PWM_LUMINANCE_SHIFT; |
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} |
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return retval; |
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} |
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/* |
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* Create a default correction table for PWM values to create linear brightness |
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* for LED based backlights using the CIE1931 algorithm. |
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*/ |
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static |
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int pwm_backlight_brightness_default(struct device *dev, |
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struct platform_pwm_backlight_data *data, |
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unsigned int period) |
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{ |
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unsigned int i; |
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u64 retval; |
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|
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/* |
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* Once we have 4096 levels there's little point going much higher... |
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* neither interactive sliders nor animation benefits from having |
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* more values in the table. |
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*/ |
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data->max_brightness = |
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min((int)DIV_ROUND_UP(period, fls(period)), 4096); |
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data->levels = devm_kcalloc(dev, data->max_brightness, |
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sizeof(*data->levels), GFP_KERNEL); |
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if (!data->levels) |
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return -ENOMEM; |
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/* Fill the table using the cie1931 algorithm */ |
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for (i = 0; i < data->max_brightness; i++) { |
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retval = cie1931((i * PWM_LUMINANCE_SCALE) / |
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data->max_brightness) * period; |
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retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE); |
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if (retval > UINT_MAX) |
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return -EINVAL; |
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data->levels[i] = (unsigned int)retval; |
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} |
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data->dft_brightness = data->max_brightness / 2; |
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data->max_brightness--; |
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return 0; |
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} |
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static int pwm_backlight_parse_dt(struct device *dev, |
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struct platform_pwm_backlight_data *data) |
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{ |
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struct device_node *node = dev->of_node; |
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unsigned int num_levels; |
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unsigned int num_steps = 0; |
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struct property *prop; |
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unsigned int *table; |
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int length; |
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u32 value; |
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int ret; |
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if (!node) |
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return -ENODEV; |
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memset(data, 0, sizeof(*data)); |
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/* |
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* These values are optional and set as 0 by default, the out values |
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* are modified only if a valid u32 value can be decoded. |
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*/ |
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of_property_read_u32(node, "post-pwm-on-delay-ms", |
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&data->post_pwm_on_delay); |
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of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay); |
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/* |
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* Determine the number of brightness levels, if this property is not |
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* set a default table of brightness levels will be used. |
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*/ |
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prop = of_find_property(node, "brightness-levels", &length); |
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if (!prop) |
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return 0; |
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num_levels = length / sizeof(u32); |
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/* read brightness levels from DT property */ |
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if (num_levels > 0) { |
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size_t size = sizeof(*data->levels) * num_levels; |
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data->levels = devm_kzalloc(dev, size, GFP_KERNEL); |
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if (!data->levels) |
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return -ENOMEM; |
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ret = of_property_read_u32_array(node, "brightness-levels", |
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data->levels, |
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num_levels); |
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if (ret < 0) |
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return ret; |
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ret = of_property_read_u32(node, "default-brightness-level", |
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&value); |
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if (ret < 0) |
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return ret; |
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data->dft_brightness = value; |
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/* |
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* This property is optional, if is set enables linear |
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* interpolation between each of the values of brightness levels |
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* and creates a new pre-computed table. |
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*/ |
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of_property_read_u32(node, "num-interpolated-steps", |
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&num_steps); |
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/* |
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* Make sure that there is at least two entries in the |
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* brightness-levels table, otherwise we can't interpolate |
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* between two points. |
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*/ |
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if (num_steps) { |
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unsigned int num_input_levels = num_levels; |
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unsigned int i; |
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u32 x1, x2, x, dx; |
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u32 y1, y2; |
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s64 dy; |
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if (num_input_levels < 2) { |
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dev_err(dev, "can't interpolate\n"); |
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return -EINVAL; |
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} |
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/* |
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* Recalculate the number of brightness levels, now |
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* taking in consideration the number of interpolated |
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* steps between two levels. |
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*/ |
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num_levels = (num_input_levels - 1) * num_steps + 1; |
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dev_dbg(dev, "new number of brightness levels: %d\n", |
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num_levels); |
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/* |
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* Create a new table of brightness levels with all the |
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* interpolated steps. |
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*/ |
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size = sizeof(*table) * num_levels; |
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table = devm_kzalloc(dev, size, GFP_KERNEL); |
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if (!table) |
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return -ENOMEM; |
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/* |
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* Fill the interpolated table[x] = y |
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* by draw lines between each (x1, y1) to (x2, y2). |
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*/ |
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dx = num_steps; |
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for (i = 0; i < num_input_levels - 1; i++) { |
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x1 = i * dx; |
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x2 = x1 + dx; |
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y1 = data->levels[i]; |
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y2 = data->levels[i + 1]; |
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dy = (s64)y2 - y1; |
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for (x = x1; x < x2; x++) { |
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table[x] = y1 + |
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div_s64(dy * (x - x1), dx); |
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} |
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} |
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/* Fill in the last point, since no line starts here. */ |
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table[x2] = y2; |
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/* |
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* As we use interpolation lets remove current |
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* brightness levels table and replace for the |
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* new interpolated table. |
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*/ |
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devm_kfree(dev, data->levels); |
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data->levels = table; |
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} |
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data->max_brightness = num_levels - 1; |
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} |
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return 0; |
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} |
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static const struct of_device_id pwm_backlight_of_match[] = { |
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{ .compatible = "pwm-backlight" }, |
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{ } |
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}; |
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MODULE_DEVICE_TABLE(of, pwm_backlight_of_match); |
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#else |
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static int pwm_backlight_parse_dt(struct device *dev, |
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struct platform_pwm_backlight_data *data) |
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{ |
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return -ENODEV; |
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} |
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static |
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int pwm_backlight_brightness_default(struct device *dev, |
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struct platform_pwm_backlight_data *data, |
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unsigned int period) |
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{ |
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return -ENODEV; |
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} |
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#endif |
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static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data) |
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{ |
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unsigned int nlevels = data->max_brightness + 1; |
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unsigned int min_val = data->levels[0]; |
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unsigned int max_val = data->levels[nlevels - 1]; |
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/* |
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* Multiplying by 128 means that even in pathological cases such |
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* as (max_val - min_val) == nlevels the error at max_val is less |
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* than 1%. |
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*/ |
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unsigned int slope = (128 * (max_val - min_val)) / nlevels; |
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unsigned int margin = (max_val - min_val) / 20; /* 5% */ |
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int i; |
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for (i = 1; i < nlevels; i++) { |
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unsigned int linear_value = min_val + ((i * slope) / 128); |
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unsigned int delta = abs(linear_value - data->levels[i]); |
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|
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if (delta > margin) |
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return false; |
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} |
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return true; |
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} |
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static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb) |
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{ |
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struct device_node *node = pb->dev->of_node; |
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|
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/* Not booted with device tree or no phandle link to the node */ |
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if (!node || !node->phandle) |
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return FB_BLANK_UNBLANK; |
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|
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/* |
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* If the driver is probed from the device tree and there is a |
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* phandle link pointing to the backlight node, it is safe to |
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* assume that another driver will enable the backlight at the |
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* appropriate time. Therefore, if it is disabled, keep it so. |
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*/ |
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/* if the enable GPIO is disabled, do not enable the backlight */ |
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if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0) |
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return FB_BLANK_POWERDOWN; |
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/* The regulator is disabled, do not enable the backlight */ |
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if (!regulator_is_enabled(pb->power_supply)) |
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return FB_BLANK_POWERDOWN; |
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/* The PWM is disabled, keep it like this */ |
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if (!pwm_is_enabled(pb->pwm)) |
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return FB_BLANK_POWERDOWN; |
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return FB_BLANK_UNBLANK; |
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} |
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static int pwm_backlight_probe(struct platform_device *pdev) |
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{ |
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struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev); |
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struct platform_pwm_backlight_data defdata; |
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struct backlight_properties props; |
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struct backlight_device *bl; |
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struct device_node *node = pdev->dev.of_node; |
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struct pwm_bl_data *pb; |
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struct pwm_state state; |
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unsigned int i; |
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int ret; |
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|
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if (!data) { |
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ret = pwm_backlight_parse_dt(&pdev->dev, &defdata); |
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if (ret < 0) { |
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dev_err(&pdev->dev, "failed to find platform data\n"); |
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return ret; |
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} |
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data = &defdata; |
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} |
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if (data->init) { |
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ret = data->init(&pdev->dev); |
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if (ret < 0) |
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return ret; |
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} |
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pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL); |
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if (!pb) { |
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ret = -ENOMEM; |
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goto err_alloc; |
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} |
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pb->notify = data->notify; |
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pb->notify_after = data->notify_after; |
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pb->check_fb = data->check_fb; |
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pb->exit = data->exit; |
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pb->dev = &pdev->dev; |
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pb->enabled = false; |
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pb->post_pwm_on_delay = data->post_pwm_on_delay; |
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pb->pwm_off_delay = data->pwm_off_delay; |
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pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable", |
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GPIOD_ASIS); |
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if (IS_ERR(pb->enable_gpio)) { |
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ret = PTR_ERR(pb->enable_gpio); |
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goto err_alloc; |
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} |
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|
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/* |
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* If the GPIO is not known to be already configured as output, that |
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* is, if gpiod_get_direction returns either 1 or -EINVAL, change the |
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* direction to output and set the GPIO as active. |
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* Do not force the GPIO to active when it was already output as it |
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* could cause backlight flickering or we would enable the backlight too |
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* early. Leave the decision of the initial backlight state for later. |
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*/ |
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if (pb->enable_gpio && |
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gpiod_get_direction(pb->enable_gpio) != 0) |
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gpiod_direction_output(pb->enable_gpio, 1); |
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|
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pb->power_supply = devm_regulator_get(&pdev->dev, "power"); |
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if (IS_ERR(pb->power_supply)) { |
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ret = PTR_ERR(pb->power_supply); |
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goto err_alloc; |
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} |
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pb->pwm = devm_pwm_get(&pdev->dev, NULL); |
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if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) { |
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dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n"); |
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pb->legacy = true; |
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pb->pwm = pwm_request(data->pwm_id, "pwm-backlight"); |
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} |
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|
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if (IS_ERR(pb->pwm)) { |
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ret = PTR_ERR(pb->pwm); |
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if (ret != -EPROBE_DEFER) |
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dev_err(&pdev->dev, "unable to request PWM\n"); |
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goto err_alloc; |
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} |
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dev_dbg(&pdev->dev, "got pwm for backlight\n"); |
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|
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/* Sync up PWM state. */ |
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pwm_init_state(pb->pwm, &state); |
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|
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/* |
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* The DT case will set the pwm_period_ns field to 0 and store the |
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* period, parsed from the DT, in the PWM device. For the non-DT case, |
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* set the period from platform data if it has not already been set |
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* via the PWM lookup table. |
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*/ |
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if (!state.period && (data->pwm_period_ns > 0)) |
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state.period = data->pwm_period_ns; |
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|
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ret = pwm_apply_state(pb->pwm, &state); |
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if (ret) { |
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dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n", |
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ret); |
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goto err_alloc; |
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} |
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|
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memset(&props, 0, sizeof(struct backlight_properties)); |
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|
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if (data->levels) { |
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pb->levels = data->levels; |
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|
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/* |
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* For the DT case, only when brightness levels is defined |
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* data->levels is filled. For the non-DT case, data->levels |
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* can come from platform data, however is not usual. |
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*/ |
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for (i = 0; i <= data->max_brightness; i++) |
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if (data->levels[i] > pb->scale) |
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pb->scale = data->levels[i]; |
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|
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if (pwm_backlight_is_linear(data)) |
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props.scale = BACKLIGHT_SCALE_LINEAR; |
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else |
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props.scale = BACKLIGHT_SCALE_NON_LINEAR; |
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} else if (!data->max_brightness) { |
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/* |
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* If no brightness levels are provided and max_brightness is |
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* not set, use the default brightness table. For the DT case, |
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* max_brightness is set to 0 when brightness levels is not |
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* specified. For the non-DT case, max_brightness is usually |
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* set to some value. |
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*/ |
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|
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/* Get the PWM period (in nanoseconds) */ |
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pwm_get_state(pb->pwm, &state); |
|
|
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ret = pwm_backlight_brightness_default(&pdev->dev, data, |
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state.period); |
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if (ret < 0) { |
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dev_err(&pdev->dev, |
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"failed to setup default brightness table\n"); |
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goto err_alloc; |
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} |
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|
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for (i = 0; i <= data->max_brightness; i++) { |
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if (data->levels[i] > pb->scale) |
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pb->scale = data->levels[i]; |
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|
|
pb->levels = data->levels; |
|
} |
|
|
|
props.scale = BACKLIGHT_SCALE_NON_LINEAR; |
|
} else { |
|
/* |
|
* That only happens for the non-DT case, where platform data |
|
* sets the max_brightness value. |
|
*/ |
|
pb->scale = data->max_brightness; |
|
} |
|
|
|
pb->lth_brightness = data->lth_brightness * (div_u64(state.period, |
|
pb->scale)); |
|
|
|
props.type = BACKLIGHT_RAW; |
|
props.max_brightness = data->max_brightness; |
|
bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb, |
|
&pwm_backlight_ops, &props); |
|
if (IS_ERR(bl)) { |
|
dev_err(&pdev->dev, "failed to register backlight\n"); |
|
ret = PTR_ERR(bl); |
|
if (pb->legacy) |
|
pwm_free(pb->pwm); |
|
goto err_alloc; |
|
} |
|
|
|
if (data->dft_brightness > data->max_brightness) { |
|
dev_warn(&pdev->dev, |
|
"invalid default brightness level: %u, using %u\n", |
|
data->dft_brightness, data->max_brightness); |
|
data->dft_brightness = data->max_brightness; |
|
} |
|
|
|
bl->props.brightness = data->dft_brightness; |
|
bl->props.power = pwm_backlight_initial_power_state(pb); |
|
backlight_update_status(bl); |
|
|
|
platform_set_drvdata(pdev, bl); |
|
return 0; |
|
|
|
err_alloc: |
|
if (data->exit) |
|
data->exit(&pdev->dev); |
|
return ret; |
|
} |
|
|
|
static int pwm_backlight_remove(struct platform_device *pdev) |
|
{ |
|
struct backlight_device *bl = platform_get_drvdata(pdev); |
|
struct pwm_bl_data *pb = bl_get_data(bl); |
|
|
|
backlight_device_unregister(bl); |
|
pwm_backlight_power_off(pb); |
|
|
|
if (pb->exit) |
|
pb->exit(&pdev->dev); |
|
if (pb->legacy) |
|
pwm_free(pb->pwm); |
|
|
|
return 0; |
|
} |
|
|
|
static void pwm_backlight_shutdown(struct platform_device *pdev) |
|
{ |
|
struct backlight_device *bl = platform_get_drvdata(pdev); |
|
struct pwm_bl_data *pb = bl_get_data(bl); |
|
|
|
pwm_backlight_power_off(pb); |
|
} |
|
|
|
#ifdef CONFIG_PM_SLEEP |
|
static int pwm_backlight_suspend(struct device *dev) |
|
{ |
|
struct backlight_device *bl = dev_get_drvdata(dev); |
|
struct pwm_bl_data *pb = bl_get_data(bl); |
|
|
|
if (pb->notify) |
|
pb->notify(pb->dev, 0); |
|
|
|
pwm_backlight_power_off(pb); |
|
|
|
if (pb->notify_after) |
|
pb->notify_after(pb->dev, 0); |
|
|
|
return 0; |
|
} |
|
|
|
static int pwm_backlight_resume(struct device *dev) |
|
{ |
|
struct backlight_device *bl = dev_get_drvdata(dev); |
|
|
|
backlight_update_status(bl); |
|
|
|
return 0; |
|
} |
|
#endif |
|
|
|
static const struct dev_pm_ops pwm_backlight_pm_ops = { |
|
#ifdef CONFIG_PM_SLEEP |
|
.suspend = pwm_backlight_suspend, |
|
.resume = pwm_backlight_resume, |
|
.poweroff = pwm_backlight_suspend, |
|
.restore = pwm_backlight_resume, |
|
#endif |
|
}; |
|
|
|
static struct platform_driver pwm_backlight_driver = { |
|
.driver = { |
|
.name = "pwm-backlight", |
|
.pm = &pwm_backlight_pm_ops, |
|
.of_match_table = of_match_ptr(pwm_backlight_of_match), |
|
}, |
|
.probe = pwm_backlight_probe, |
|
.remove = pwm_backlight_remove, |
|
.shutdown = pwm_backlight_shutdown, |
|
}; |
|
|
|
module_platform_driver(pwm_backlight_driver); |
|
|
|
MODULE_DESCRIPTION("PWM based Backlight Driver"); |
|
MODULE_LICENSE("GPL v2"); |
|
MODULE_ALIAS("platform:pwm-backlight");
|
|
|