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pwm-backlight: Add rudimentary device tree support

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This commit adds very basic support for device tree probing. Currently,
only a PWM and a list of distinct brightness levels can be specified.
Enabling or disabling backlight power via GPIOs is not yet supported.

Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
This commit is contained in:
Thierry Reding
2011-12-16 21:25:29 +01:00
parent 4dce82c1e8
commit 3e3ed6cdc4
4 changed files with 159 additions and 21 deletions
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28
Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt Normal file
View File

@@ -0,0 +1,28 @@
pwm-backlight bindings
Required properties:
- compatible: "pwm-backlight"
- pwms: OF device-tree PWM specification (see PWM binding[0])
- brightness-levels: Array of distinct brightness levels. Typically these
are in the range from 0 to 255, but any range starting at 0 will do.
The actual brightness level (PWM duty cycle) will be interpolated
from these values. 0 means a 0% duty cycle (darkest/off), while the
last value in the array represents a 100% duty cycle (brightest).
- default-brightness-level: the default brightness level (index into the
array defined by the "brightness-levels" property)
Optional properties:
- pwm-names: a list of names for the PWM devices specified in the
"pwms" property (see PWM binding[0])
[0]: Documentation/devicetree/bindings/pwm/pwm.txt
Example:
backlight {
compatible = "pwm-backlight";
pwms = <&pwm 0 5000000>;
brightness-levels = <0 4 8 16 32 64 128 255>;
default-brightness-level = <6>;
};

2
drivers/video/backlight/Kconfig
View File

@@ -245,7 +245,7 @@ config BACKLIGHT_CARILLO_RANCH
config BACKLIGHT_PWM
tristate "Generic PWM based Backlight Driver"
depends on HAVE_PWM
depends on PWM
help
If you have a LCD backlight adjustable by PWM, say Y to enable
this driver.

135
drivers/video/backlight/pwm_bl.c
View File

@@ -26,11 +26,13 @@ struct pwm_bl_data {
struct device *dev;
unsigned int period;
unsigned int lth_brightness;
unsigned int *levels;
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 int pwm_backlight_update_status(struct backlight_device *bl)
@@ -52,6 +54,11 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
pwm_config(pb->pwm, 0, pb->period);
pwm_disable(pb->pwm);
} else {
if (pb->levels) {
brightness = pb->levels[brightness];
max = pb->levels[max];
}
brightness = pb->lth_brightness +
(brightness * (pb->period - pb->lth_brightness) / max);
pwm_config(pb->pwm, brightness, pb->period);
@@ -83,17 +90,98 @@ static const struct backlight_ops pwm_backlight_ops = {
.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;
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;
if (value >= data->max_brightness) {
dev_warn(dev, "invalid default brightness level: %u, using %u\n",
value, data->max_brightness - 1);
value = data->max_brightness - 1;
}
data->dft_brightness = value;
data->max_brightness--;
}
/*
* TODO: Most users of this driver use a number of GPIOs to control
* backlight power. Support for specifying these needs to be
* added.
*/
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 backlight_properties props;
struct platform_pwm_backlight_data *data = pdev->dev.platform_data;
struct platform_pwm_backlight_data defdata;
struct backlight_properties props;
struct backlight_device *bl;
struct pwm_bl_data *pb;
unsigned int max;
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 -EINVAL;
return ret;
}
data = &defdata;
}
if (data->init) {
@@ -109,22 +197,43 @@ static int pwm_backlight_probe(struct platform_device *pdev)
goto err_alloc;
}
pb->period = data->pwm_period_ns;
if (data->levels) {
max = data->levels[data->max_brightness];
pb->levels = data->levels;
} else
max = data->max_brightness;
pb->notify = data->notify;
pb->notify_after = data->notify_after;
pb->check_fb = data->check_fb;
pb->lth_brightness = data->lth_brightness *
(data->pwm_period_ns / data->max_brightness);
pb->exit = data->exit;
pb->dev = &pdev->dev;
pb->pwm = pwm_request(data->pwm_id, "backlight");
pb->pwm = pwm_get(&pdev->dev, NULL);
if (IS_ERR(pb->pwm)) {
dev_err(&pdev->dev, "unable to request PWM for backlight\n");
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_alloc;
} else
}
}
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 / max);
memset(&props, 0, sizeof(struct backlight_properties));
props.type = BACKLIGHT_RAW;
props.max_brightness = data->max_brightness;
@@ -143,7 +252,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
return 0;
err_bl:
pwm_free(pb->pwm);
pwm_put(pb->pwm);
err_alloc:
if (data->exit)
data->exit(&pdev->dev);
@@ -152,16 +261,15 @@ err_alloc:
static int pwm_backlight_remove(struct platform_device *pdev)
{
struct platform_pwm_backlight_data *data = pdev->dev.platform_data;
struct backlight_device *bl = platform_get_drvdata(pdev);
struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);
backlight_device_unregister(bl);
pwm_config(pb->pwm, 0, pb->period);
pwm_disable(pb->pwm);
pwm_free(pb->pwm);
if (data->exit)
data->exit(&pdev->dev);
pwm_put(pb->pwm);
if (pb->exit)
pb->exit(&pdev->dev);
return 0;
}
@@ -200,6 +308,7 @@ static struct platform_driver pwm_backlight_driver = {
#ifdef CONFIG_PM
.pm = &pwm_backlight_pm_ops,
#endif
.of_match_table = of_match_ptr(pwm_backlight_of_match),
},
.probe = pwm_backlight_probe,
.remove = pwm_backlight_remove,

1
include/linux/pwm_backlight.h
View File

@@ -12,6 +12,7 @@ struct platform_pwm_backlight_data {
unsigned int dft_brightness;
unsigned int lth_brightness;
unsigned int pwm_period_ns;
unsigned int *levels;
int (*init)(struct device *dev);
int (*notify)(struct device *dev, int brightness);
void (*notify_after)(struct device *dev, int brightness);