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// SPDX-License-Identifier: GPL-2.0-only
/*
* Backlight driver for the Kinetic KTD253
* Based on code and know-how from the Samsung GT-S7710
* Gareth Phillips <gareth.phillips@samsung.com>
*/
#include <linux/backlight.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/fb.h>
#include <linux/gpio/consumer.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/limits.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/property.h>
#include <linux/slab.h>
/* Current ratio is n/32 from 1/32 to 32/32 */
#define KTD253_MIN_RATIO 1
#define KTD253_MAX_RATIO 32
#define KTD253_DEFAULT_RATIO 13
#define KTD253_T_LOW_NS (200 + 10) /* Additional 10ns as safety factor */
#define KTD253_T_HIGH_NS (200 + 10) /* Additional 10ns as safety factor */
#define KTD253_T_OFF_CRIT_NS 100000 /* 100 us, now it doesn't look good */
#define KTD253_T_OFF_MS 3
struct ktd253_backlight {
struct device *dev;
struct backlight_device *bl;
struct gpio_desc *gpiod;
u16 ratio;
};
static void ktd253_backlight_set_max_ratio(struct ktd253_backlight *ktd253)
{
gpiod_set_value_cansleep(ktd253->gpiod, 1);
ndelay(KTD253_T_HIGH_NS);
/* We always fall back to this when we power on */
}
static int ktd253_backlight_stepdown(struct ktd253_backlight *ktd253)
{
/*
* These GPIO operations absolutely can NOT sleep so no _cansleep
* suffixes, and no using GPIO expanders on slow buses for this!
*
* The maximum number of cycles of the loop is 32 so the time taken
* should nominally be:
* (T_LOW_NS + T_HIGH_NS + loop_time) * 32
*
* Architectures do not always support ndelay() and we will get a few us
* instead. If we get to a critical time limit an interrupt has likely
* occured in the low part of the loop and we need to restart from the
* top so we have the backlight in a known state.
*/
u64 ns;
ns = ktime_get_ns();
gpiod_set_value(ktd253->gpiod, 0);
ndelay(KTD253_T_LOW_NS);
gpiod_set_value(ktd253->gpiod, 1);
ns = ktime_get_ns() - ns;
if (ns >= KTD253_T_OFF_CRIT_NS) {
dev_err(ktd253->dev, "PCM on backlight took too long (%llu ns)\n", ns);
return -EAGAIN;
}
ndelay(KTD253_T_HIGH_NS);
return 0;
}
static int ktd253_backlight_update_status(struct backlight_device *bl)
{
struct ktd253_backlight *ktd253 = bl_get_data(bl);
int brightness = backlight_get_brightness(bl);
u16 target_ratio;
u16 current_ratio = ktd253->ratio;
int ret;
dev_dbg(ktd253->dev, "new brightness/ratio: %d/32\n", brightness);
target_ratio = brightness;
if (target_ratio == current_ratio)
/* This is already right */
return 0;
if (target_ratio == 0) {
gpiod_set_value_cansleep(ktd253->gpiod, 0);
/*
* We need to keep the GPIO low for at least this long
* to actually switch the KTD253 off.
*/
msleep(KTD253_T_OFF_MS);
ktd253->ratio = 0;
return 0;
}
if (current_ratio == 0) {
ktd253_backlight_set_max_ratio(ktd253);
current_ratio = KTD253_MAX_RATIO;
}
while (current_ratio != target_ratio) {
/*
* These GPIO operations absolutely can NOT sleep so no
* _cansleep suffixes, and no using GPIO expanders on
* slow buses for this!
*/
ret = ktd253_backlight_stepdown(ktd253);
if (ret == -EAGAIN) {
/*
* Something disturbed the backlight setting code when
* running so we need to bring the PWM back to a known
* state. This shouldn't happen too much.
*/
gpiod_set_value_cansleep(ktd253->gpiod, 0);
msleep(KTD253_T_OFF_MS);
ktd253_backlight_set_max_ratio(ktd253);
current_ratio = KTD253_MAX_RATIO;
} else if (current_ratio == KTD253_MIN_RATIO) {
/* After 1/32 we loop back to 32/32 */
current_ratio = KTD253_MAX_RATIO;
} else {
current_ratio--;
}
}
ktd253->ratio = current_ratio;
dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio);
return 0;
}
static const struct backlight_ops ktd253_backlight_ops = {
.options = BL_CORE_SUSPENDRESUME,
.update_status = ktd253_backlight_update_status,
};
static int ktd253_backlight_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
struct backlight_device *bl;
struct ktd253_backlight *ktd253;
u32 max_brightness;
u32 brightness;
int ret;
ktd253 = devm_kzalloc(dev, sizeof(*ktd253), GFP_KERNEL);
if (!ktd253)
return -ENOMEM;
ktd253->dev = dev;
ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
if (ret)
max_brightness = KTD253_MAX_RATIO;
if (max_brightness > KTD253_MAX_RATIO) {
/* Clamp brightness to hardware max */
dev_err(dev, "illegal max brightness specified\n");
max_brightness = KTD253_MAX_RATIO;
}
ret = device_property_read_u32(dev, "default-brightness", &brightness);
if (ret)
brightness = KTD253_DEFAULT_RATIO;
if (brightness > max_brightness) {
/* Clamp default brightness to max brightness */
dev_err(dev, "default brightness exceeds max brightness\n");
brightness = max_brightness;
}
if (brightness)
/* This will be the default ratio when the KTD253 is enabled */
ktd253->ratio = KTD253_MAX_RATIO;
else
ktd253->ratio = 0;
ktd253->gpiod = devm_gpiod_get(dev, "enable",
brightness ? GPIOD_OUT_HIGH :
GPIOD_OUT_LOW);
if (IS_ERR(ktd253->gpiod)) {
ret = PTR_ERR(ktd253->gpiod);
if (ret != -EPROBE_DEFER)
dev_err(dev, "gpio line missing or invalid.\n");
return ret;
}
gpiod_set_consumer_name(ktd253->gpiod, dev_name(dev));
bl = devm_backlight_device_register(dev, dev_name(dev), dev, ktd253,
&ktd253_backlight_ops, NULL);
if (IS_ERR(bl)) {
dev_err(dev, "failed to register backlight\n");
return PTR_ERR(bl);
}
bl->props.max_brightness = max_brightness;
/* When we just enable the GPIO line we set max brightness */
if (brightness) {
bl->props.brightness = brightness;
bl->props.power = FB_BLANK_UNBLANK;
} else {
bl->props.brightness = 0;
bl->props.power = FB_BLANK_POWERDOWN;
}
ktd253->bl = bl;
platform_set_drvdata(pdev, bl);
backlight_update_status(bl);
return 0;
}
static const struct of_device_id ktd253_backlight_of_match[] = {
{ .compatible = "kinetic,ktd253" },
{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match);
static struct platform_driver ktd253_backlight_driver = {
.driver = {
.name = "ktd253-backlight",
.of_match_table = ktd253_backlight_of_match,
},
.probe = ktd253_backlight_probe,
};
module_platform_driver(ktd253_backlight_driver);
MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:ktd253-backlight");
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