imx6q上的背光驱动分析
imx6q设备树上的pwm背光驱动描述如下，各节点的具体含义可参考http://blog.csdn.net/mike8825/article/details/51656400
pwm-backlight {
compatible = "pwm-backlight";
pwms = <&pwm1 0 50000>;
brightness-levels = <
0 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26 27 28 29
30 31 32 33 34 35 36 37 38 39
40 41 42 43 44 45 46 47 48 49
50 51 52 53 54 55 56 57 58 59
60 61 62 63 64 65 66 67 68 69
70 71 72 73 74 75 76 77 78 79
80 81 82 83 84 85 86 87 88 89
90 91 92 93 94 95 96 97 98 99
100
>;
default-brightness-level = <94>;
};&pwm1 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_pwm1>;
status = "okay";
};pinctrl_pwm1: pwm1grp {
fsl,pins = <
MX6QDL_PAD_SD1_DAT3__PWM1_OUT 0x1b0b1
>;
};具体的驱动文件是imx6qdl-sabresd/kernel_imx/drivers/video/backlight/pwm_bl.c
/*
* linux/drivers/video/backlight/pwm_bl.c
*
* simple PWM based backlight control, board code has to setup
* 1) pin configuration so PWM waveforms can output
* 2) platform_data being correctly configured
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
struct pwm_bl_data {
struct pwm_device *pwm;
struct device *dev;
unsigned int period;
unsigned int lth_brightness;
unsigned int *levels;
bool enabled;
struct regulator *power_supply;
int enable_gpio;
unsigned long enable_gpio_flags;
unsigned int scale;
int (*notify)(struct device *,
int brightness);
void (*notify_after)(struct device *,
int brightness);
int (*check_fb)(struct device *, struct fb_info *);
void (*exit)(struct device *);
};
static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)
{
int err;
if (pb->enabled)
return;
err = regulator_enable(pb->power_supply);
if (err < 0)
dev_err(pb->dev, "failed to enable power supply\n");
if (gpio_is_valid(pb->enable_gpio)) {
if (pb->enable_gpio_flags & PWM_BACKLIGHT_GPIO_ACTIVE_LOW)
gpio_set_value(pb->enable_gpio, 0);
else
gpio_set_value(pb->enable_gpio, 1);
}
pwm_enable(pb->pwm);
pb->enabled = true;
}
static void pwm_backlight_power_off(struct pwm_bl_data *pb)
{
if (!pb->enabled)
return;
pwm_config(pb->pwm, 0, pb->period);
pwm_disable(pb->pwm);
if (gpio_is_valid(pb->enable_gpio)) {
if (pb->enable_gpio_flags & PWM_BACKLIGHT_GPIO_ACTIVE_LOW)
gpio_set_value(pb->enable_gpio, 1);
else
gpio_set_value(pb->enable_gpio, 0);
}
regulator_disable(pb->power_supply);
pb->enabled = false;
}
static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
{
unsigned int lth = pb->lth_brightness;
int duty_cycle;
if (pb->levels)
duty_cycle = pb->levels[brightness];
else
duty_cycle = brightness;
return (duty_cycle * (pb->period - lth) / pb->scale) + lth;
}
static int pwm_backlight_update_status(struct backlight_device *bl)
{
struct pwm_bl_data *pb = bl_get_data(bl);
int brightness = bl->props.brightness;
int duty_cycle;
if (bl->props.power != FB_BLANK_UNBLANK ||
bl->props.fb_blank != FB_BLANK_UNBLANK ||
bl->props.state & BL_CORE_FBBLANK)
brightness = 0;
if (pb->notify)
brightness = pb->notify(pb->dev, brightness);
if (brightness > 0) {
duty_cycle = compute_duty_cycle(pb, brightness);
pwm_config(pb->pwm, duty_cycle, pb->period);
pwm_backlight_power_on(pb, brightness);
} else
pwm_backlight_power_off(pb);
if (pb->notify_after)
pb->notify_after(pb->dev, brightness);
return 0;
}
static int pwm_backlight_get_brightness(struct backlight_device *bl)
{
return bl->props.brightness;
}
static int pwm_backlight_check_fb(struct backlight_device *bl,
struct fb_info *info)
{
struct pwm_bl_data *pb = bl_get_data(bl);
return !pb->check_fb || pb->check_fb(pb->dev, info);
}
static const struct backlight_ops pwm_backlight_ops = {
.update_status = pwm_backlight_update_status,
.get_brightness = pwm_backlight_get_brightness,
.check_fb = pwm_backlight_check_fb,
};
#ifdef CONFIG_OF
static int pwm_backlight_parse_dt(struct device *dev,
struct platform_pwm_backlight_data *data)
{
struct device_node *node = dev->of_node;
enum of_gpio_flags flags;
struct property *prop;
int length;
u32 value;
int ret;
if (!node)
return -ENODEV;
memset(data, 0, sizeof(*data));
/* determine the number of brightness levels */
prop = of_find_property(node, "brightness-levels", &length);
if (!prop)
return -EINVAL;
data->max_brightness = length / sizeof(u32);
/* read brightness levels from DT property */
if (data->max_brightness > 0) {
size_t size = sizeof(*data->levels) * data->max_brightness;
data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
if (!data->levels)
return -ENOMEM;
ret = of_property_read_u32_array(node, "brightness-levels",
data->levels,
data->max_brightness);
if (ret < 0)
return ret;
ret = of_property_read_u32(node, "default-brightness-level",
&value);
if (ret < 0)
return ret;
data->dft_brightness = value;
data->max_brightness--;
}
data->enable_gpio = of_get_named_gpio_flags(node, "enable-gpios", 0,
&flags);
if (data->enable_gpio == -EPROBE_DEFER)
return -EPROBE_DEFER;
if (gpio_is_valid(data->enable_gpio) && (flags & OF_GPIO_ACTIVE_LOW))
data->enable_gpio_flags |= PWM_BACKLIGHT_GPIO_ACTIVE_LOW;
return 0;
}
static struct of_device_id pwm_backlight_of_match[] = {
{ .compatible = "pwm-backlight" },
{ }
};
MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
#else
static int pwm_backlight_parse_dt(struct device *dev,
struct platform_pwm_backlight_data *data)
{
return -ENODEV;
}
#endif
static int pwm_backlight_probe(struct platform_device *pdev)
{
struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
struct platform_pwm_backlight_data defdata;
struct backlight_properties props;
struct backlight_device *bl;
struct pwm_bl_data *pb;
int ret;
if (!data) {
ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
if (ret < 0) {
dev_err(&pdev->dev, "failed to find platform data\n");
return ret;
}
data = &defdata;
}
if (data->init) {
ret = data->init(&pdev->dev);
if (ret < 0)
return ret;
}
pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
if (!pb) {
ret = -ENOMEM;
goto err_alloc;
}
if (data->levels) {
unsigned int i;
for (i = 0; i <= data->max_brightness; i++)
if (data->levels[i] > pb->scale)
pb->scale = data->levels[i];
pb->levels = data->levels;
} else
pb->scale = data->max_brightness;
pb->enable_gpio = data->enable_gpio;
pb->enable_gpio_flags = data->enable_gpio_flags;
pb->notify = data->notify;
pb->notify_after = data->notify_after;
pb->check_fb = data->check_fb;
pb->exit = data->exit;
pb->dev = &pdev->dev;
pb->enabled = false;
if (gpio_is_valid(pb->enable_gpio)) {
unsigned long flags;
if (pb->enable_gpio_flags & PWM_BACKLIGHT_GPIO_ACTIVE_LOW)
flags = GPIOF_OUT_INIT_HIGH;
else
flags = GPIOF_OUT_INIT_LOW;
ret = gpio_request_one(pb->enable_gpio, flags, "enable");
if (ret < 0) {
dev_err(&pdev->dev, "failed to request GPIO#%d: %d\n",
pb->enable_gpio, ret);
goto err_alloc;
}
}
pb->power_supply = devm_regulator_get(&pdev->dev, "power");
if (IS_ERR(pb->power_supply)) {
ret = PTR_ERR(pb->power_supply);
goto err_gpio;
}
pb->pwm = devm_pwm_get(&pdev->dev, NULL);
if (IS_ERR(pb->pwm)) {
dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
if (IS_ERR(pb->pwm)) {
dev_err(&pdev->dev, "unable to request legacy PWM\n");
ret = PTR_ERR(pb->pwm);
goto err_gpio;
}
}
dev_dbg(&pdev->dev, "got pwm for backlight\n");
/*
* 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 (data->pwm_period_ns > 0)
pwm_set_period(pb->pwm, data->pwm_period_ns);
pb->period = pwm_get_period(pb->pwm);
pb->lth_brightness = data->lth_brightness * (pb->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);
goto err_gpio;
}
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;
backlight_update_status(bl);
platform_set_drvdata(pdev, bl);
return 0;
err_gpio:
if (gpio_is_valid(pb->enable_gpio))
gpio_free(pb->enable_gpio);
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);
return 0;
}
#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",
.owner = THIS_MODULE,
.pm = &pwm_backlight_pm_ops,
.of_match_table = of_match_ptr(pwm_backlight_of_match),
},
.probe = pwm_backlight_probe,
.remove = pwm_backlight_remove,
};
module_platform_driver(pwm_backlight_driver);
MODULE_DESCRIPTION("PWM based Backlight Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:pwm-backlight"); 通过adb进入shell终端，通过echo xxx >brightness就可改变背光亮度。
root@sabresd_6dq:/sys/class/backlight/pwm-backlight.0 # ls -al
-r--r--r-- root root 4096 1970-01-01 04:39 actual_brightness
-rw-r--r-- root root 4096 1970-01-01 04:39 bl_power
-rw-rw---- system system 4096 1970-01-01 04:30 brightness
lrwxrwxrwx root root 1970-01-01 04:39 device -> ../../../pwm-backlight.33
-r--r--r-- root root 4096 1970-01-01 04:30 max_brightness
drwxr-xr-x root root 1970-01-01 04:30 power
lrwxrwxrwx root root 1970-01-01 04:39 subsystem -> ../../../../../class/backlight
-r--r--r-- root root 4096 1970-01-01 04:39 type
-rw-r--r-- root root 4096 1970-01-01 04:30 uevent