226 lines
6.3 KiB
C
226 lines
6.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Backlight driver for the Kinetic KTD253
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* Based on code and know-how from the Samsung GT-S7710
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* Gareth Phillips <gareth.phillips@samsung.com>
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*/
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#include <linux/backlight.h>
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#include <linux/delay.h>
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#include <linux/err.h>
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#include <linux/fb.h>
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#include <linux/gpio/consumer.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/limits.h>
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#include <linux/module.h>
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#include <linux/of.h>
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#include <linux/platform_device.h>
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#include <linux/property.h>
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#include <linux/slab.h>
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/* Current ratio is n/32 from 1/32 to 32/32 */
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#define KTD253_MIN_RATIO 1
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#define KTD253_MAX_RATIO 32
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#define KTD253_DEFAULT_RATIO 13
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#define KTD253_T_LOW_NS (200 + 10) /* Additional 10ns as safety factor */
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#define KTD253_T_HIGH_NS (200 + 10) /* Additional 10ns as safety factor */
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#define KTD253_T_OFF_CRIT_NS 100000 /* 100 us, now it doesn't look good */
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#define KTD253_T_OFF_MS 3
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struct ktd253_backlight {
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struct device *dev;
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struct backlight_device *bl;
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struct gpio_desc *gpiod;
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u16 ratio;
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};
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static void ktd253_backlight_set_max_ratio(struct ktd253_backlight *ktd253)
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{
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gpiod_set_value_cansleep(ktd253->gpiod, 1);
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ndelay(KTD253_T_HIGH_NS);
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/* We always fall back to this when we power on */
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}
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static int ktd253_backlight_stepdown(struct ktd253_backlight *ktd253)
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{
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/*
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* These GPIO operations absolutely can NOT sleep so no _cansleep
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* suffixes, and no using GPIO expanders on slow buses for this!
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*
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* The maximum number of cycles of the loop is 32 so the time taken
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* should nominally be:
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* (T_LOW_NS + T_HIGH_NS + loop_time) * 32
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*
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* Architectures do not always support ndelay() and we will get a few us
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* instead. If we get to a critical time limit an interrupt has likely
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* occured in the low part of the loop and we need to restart from the
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* top so we have the backlight in a known state.
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*/
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u64 ns;
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ns = ktime_get_ns();
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gpiod_set_value(ktd253->gpiod, 0);
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ndelay(KTD253_T_LOW_NS);
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gpiod_set_value(ktd253->gpiod, 1);
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ns = ktime_get_ns() - ns;
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if (ns >= KTD253_T_OFF_CRIT_NS) {
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dev_err(ktd253->dev, "PCM on backlight took too long (%llu ns)\n", ns);
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return -EAGAIN;
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}
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ndelay(KTD253_T_HIGH_NS);
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return 0;
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}
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static int ktd253_backlight_update_status(struct backlight_device *bl)
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{
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struct ktd253_backlight *ktd253 = bl_get_data(bl);
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int brightness = backlight_get_brightness(bl);
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u16 target_ratio;
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u16 current_ratio = ktd253->ratio;
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int ret;
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dev_dbg(ktd253->dev, "new brightness/ratio: %d/32\n", brightness);
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target_ratio = brightness;
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if (target_ratio == current_ratio)
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/* This is already right */
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return 0;
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if (target_ratio == 0) {
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gpiod_set_value_cansleep(ktd253->gpiod, 0);
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/*
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* We need to keep the GPIO low for at least this long
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* to actually switch the KTD253 off.
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*/
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msleep(KTD253_T_OFF_MS);
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ktd253->ratio = 0;
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return 0;
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}
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if (current_ratio == 0) {
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ktd253_backlight_set_max_ratio(ktd253);
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current_ratio = KTD253_MAX_RATIO;
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}
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while (current_ratio != target_ratio) {
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/*
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* These GPIO operations absolutely can NOT sleep so no
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* _cansleep suffixes, and no using GPIO expanders on
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* slow buses for this!
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*/
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ret = ktd253_backlight_stepdown(ktd253);
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if (ret == -EAGAIN) {
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/*
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* Something disturbed the backlight setting code when
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* running so we need to bring the PWM back to a known
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* state. This shouldn't happen too much.
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*/
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gpiod_set_value_cansleep(ktd253->gpiod, 0);
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msleep(KTD253_T_OFF_MS);
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ktd253_backlight_set_max_ratio(ktd253);
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current_ratio = KTD253_MAX_RATIO;
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} else if (current_ratio == KTD253_MIN_RATIO) {
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/* After 1/32 we loop back to 32/32 */
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current_ratio = KTD253_MAX_RATIO;
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} else {
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current_ratio--;
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}
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}
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ktd253->ratio = current_ratio;
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dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio);
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return 0;
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}
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static const struct backlight_ops ktd253_backlight_ops = {
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.options = BL_CORE_SUSPENDRESUME,
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.update_status = ktd253_backlight_update_status,
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};
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static int ktd253_backlight_probe(struct platform_device *pdev)
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{
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struct device *dev = &pdev->dev;
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struct backlight_device *bl;
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struct ktd253_backlight *ktd253;
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u32 max_brightness;
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u32 brightness;
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int ret;
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ktd253 = devm_kzalloc(dev, sizeof(*ktd253), GFP_KERNEL);
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if (!ktd253)
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return -ENOMEM;
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ktd253->dev = dev;
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ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
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if (ret)
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max_brightness = KTD253_MAX_RATIO;
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if (max_brightness > KTD253_MAX_RATIO) {
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/* Clamp brightness to hardware max */
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dev_err(dev, "illegal max brightness specified\n");
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max_brightness = KTD253_MAX_RATIO;
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}
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ret = device_property_read_u32(dev, "default-brightness", &brightness);
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if (ret)
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brightness = KTD253_DEFAULT_RATIO;
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if (brightness > max_brightness) {
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/* Clamp default brightness to max brightness */
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dev_err(dev, "default brightness exceeds max brightness\n");
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brightness = max_brightness;
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}
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ktd253->gpiod = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
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if (IS_ERR(ktd253->gpiod))
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return dev_err_probe(dev, PTR_ERR(ktd253->gpiod),
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"gpio line missing or invalid.\n");
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gpiod_set_consumer_name(ktd253->gpiod, dev_name(dev));
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/* Bring backlight to a known off state */
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msleep(KTD253_T_OFF_MS);
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bl = devm_backlight_device_register(dev, dev_name(dev), dev, ktd253,
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&ktd253_backlight_ops, NULL);
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if (IS_ERR(bl)) {
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dev_err(dev, "failed to register backlight\n");
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return PTR_ERR(bl);
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}
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bl->props.max_brightness = max_brightness;
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/* When we just enable the GPIO line we set max brightness */
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if (brightness) {
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bl->props.brightness = brightness;
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bl->props.power = FB_BLANK_UNBLANK;
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} else {
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bl->props.brightness = 0;
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bl->props.power = FB_BLANK_POWERDOWN;
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}
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ktd253->bl = bl;
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platform_set_drvdata(pdev, bl);
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backlight_update_status(bl);
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return 0;
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}
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static const struct of_device_id ktd253_backlight_of_match[] = {
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{ .compatible = "kinetic,ktd253" },
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{ .compatible = "kinetic,ktd259" },
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{ /* sentinel */ }
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};
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MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match);
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static struct platform_driver ktd253_backlight_driver = {
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.driver = {
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.name = "ktd253-backlight",
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.of_match_table = ktd253_backlight_of_match,
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},
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.probe = ktd253_backlight_probe,
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};
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module_platform_driver(ktd253_backlight_driver);
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MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
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MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("platform:ktd253-backlight");
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