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![Enric Balletbo i Serra](/assets/img/avatar_default.png)
The "atomic" API allows us to configure PWM period and duty_cycle and enable it in one call. The patch also moves the pwm_init_state just before any use of the pwm_state struct, this fixes a potential bug where pwm_get_state can be called before pwm_init_state. Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org> Tested-by: Heiko Stuebner <heiko@sntech.de> Signed-off-by: Lee Jones <lee.jones@linaro.org>
692 lines
17 KiB
C
692 lines
17 KiB
C
/*
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* linux/drivers/video/backlight/pwm_bl.c
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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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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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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/gpio.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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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 (state.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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}
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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 (!state.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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}
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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 = bl->props.brightness;
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struct pwm_state state;
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if (bl->props.power != FB_BLANK_UNBLANK ||
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bl->props.fb_blank != FB_BLANK_UNBLANK ||
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bl->props.state & BL_CORE_FBBLANK)
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brightness = 0;
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if (pb->notify)
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brightness = pb->notify(pb->dev, brightness);
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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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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_SCALE 10000 /* luminance scale */
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/* An integer based power function */
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static u64 int_pow(u64 base, int exp)
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{
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u64 result = 1;
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while (exp) {
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if (exp & 1)
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result *= base;
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exp >>= 1;
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base *= base;
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}
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return result;
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}
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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* / 902.3) if L* ≤ 0.08856
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* Y = ((L* + 16) / 116)^3 if L* > 0.08856
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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, unsigned int scale)
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{
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u64 retval;
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lightness *= 100;
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if (lightness <= (8 * scale)) {
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retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023);
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} else {
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retval = int_pow((lightness + (16 * scale)) / 116, 3);
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retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
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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 counter = 0;
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unsigned int i, n;
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u64 retval;
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/*
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* Count the number of bits needed to represent the period number. The
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* number of bits is used to calculate the number of levels used for the
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* brightness-levels table, the purpose of this calculation is have a
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* pre-computed table with enough levels to get linear brightness
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* perception. The period is divided by the number of bits so for a
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* 8-bit PWM we have 255 / 8 = 32 brightness levels or for a 16-bit PWM
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* we have 65535 / 16 = 4096 brightness levels.
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*
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* Note that this method is based on empirical testing on different
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* devices with PWM of 8 and 16 bits of resolution.
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*/
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n = period;
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while (n) {
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counter += n % 2;
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n >>= 1;
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}
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data->max_brightness = DIV_ROUND_UP(period, counter);
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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, PWM_LUMINANCE_SCALE) *
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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 = 0;
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unsigned int levels_count;
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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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* 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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data->max_brightness = length / sizeof(u32);
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/* read brightness levels from DT property */
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if (data->max_brightness > 0) {
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size_t size = sizeof(*data->levels) * data->max_brightness;
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unsigned int i, j, n = 0;
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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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data->max_brightness);
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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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if (data->max_brightness < 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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for (i = 0; i < data->max_brightness - 1; i++) {
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if ((data->levels[i + 1] - data->levels[i]) /
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num_steps)
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num_levels += num_steps;
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else
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num_levels++;
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}
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num_levels++;
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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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/* Fill the interpolated table. */
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levels_count = 0;
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for (i = 0; i < data->max_brightness - 1; i++) {
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value = data->levels[i];
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n = (data->levels[i + 1] - value) / num_steps;
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if (n > 0) {
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for (j = 0; j < num_steps; j++) {
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table[levels_count] = value;
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value += n;
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levels_count++;
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}
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} else {
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table[levels_count] = data->levels[i];
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levels_count++;
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}
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}
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table[levels_count] = data->levels[i];
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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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* Reassign max_brightness value to the new total number
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* of brightness levels.
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*/
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data->max_brightness = num_levels;
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}
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data->max_brightness--;
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}
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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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data->enable_gpio = -EINVAL;
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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 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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/* 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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* 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(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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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->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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* Compatibility fallback for drivers still using the integer GPIO
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* platform data. Must go away soon.
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*/
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if (!pb->enable_gpio && gpio_is_valid(data->enable_gpio)) {
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ret = devm_gpio_request_one(&pdev->dev, data->enable_gpio,
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GPIOF_OUT_INIT_HIGH, "enable");
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if (ret < 0) {
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dev_err(&pdev->dev, "failed to request GPIO#%d: %d\n",
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data->enable_gpio, ret);
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goto err_alloc;
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}
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pb->enable_gpio = gpio_to_desc(data->enable_gpio);
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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)
|
|
gpiod_direction_output(pb->enable_gpio, 1);
|
|
|
|
pb->power_supply = devm_regulator_get(&pdev->dev, "power");
|
|
if (IS_ERR(pb->power_supply)) {
|
|
ret = PTR_ERR(pb->power_supply);
|
|
goto err_alloc;
|
|
}
|
|
|
|
pb->pwm = devm_pwm_get(&pdev->dev, NULL);
|
|
if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) {
|
|
dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
|
|
pb->legacy = true;
|
|
pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
|
|
}
|
|
|
|
if (IS_ERR(pb->pwm)) {
|
|
ret = PTR_ERR(pb->pwm);
|
|
if (ret != -EPROBE_DEFER)
|
|
dev_err(&pdev->dev, "unable to request PWM\n");
|
|
goto err_alloc;
|
|
}
|
|
|
|
dev_dbg(&pdev->dev, "got pwm for backlight\n");
|
|
|
|
/* Sync up PWM state. */
|
|
pwm_init_state(pb->pwm, &state);
|
|
|
|
/*
|
|
* The DT case will set the pwm_period_ns field to 0 and store the
|
|
* period, parsed from the DT, in the PWM device. For the non-DT case,
|
|
* set the period from platform data if it has not already been set
|
|
* via the PWM lookup table.
|
|
*/
|
|
if (!state.period && (data->pwm_period_ns > 0))
|
|
state.period = data->pwm_period_ns;
|
|
|
|
ret = pwm_apply_state(pb->pwm, &state);
|
|
if (ret) {
|
|
dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
|
|
ret);
|
|
goto err_alloc;
|
|
}
|
|
|
|
if (!data->levels) {
|
|
ret = pwm_backlight_brightness_default(&pdev->dev, data,
|
|
state.period);
|
|
if (ret < 0) {
|
|
dev_err(&pdev->dev,
|
|
"failed to setup default brightness table\n");
|
|
goto err_alloc;
|
|
}
|
|
}
|
|
|
|
for (i = 0; i <= data->max_brightness; i++) {
|
|
if (data->levels[i] > pb->scale)
|
|
pb->scale = data->levels[i];
|
|
|
|
pb->levels = data->levels;
|
|
}
|
|
|
|
pb->lth_brightness = data->lth_brightness * (state.period / pb->scale);
|
|
|
|
memset(&props, 0, sizeof(struct backlight_properties));
|
|
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");
|
|
MODULE_ALIAS("platform:pwm-backlight");
|