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daa3736151
Remove interrupt disablement during backlight setting. It is
way to dangerous and makes platforms instable by having it
miss vblank IRQs leading to the graphics derailing.
The code is using ndelay() which is not available on
platforms such as ARM and will result in 32 * udelay(1)
which is substantial.
Add some code to detect if an interrupt occurs during the
tight loop and in that case just redo it from the top.
Fixes: 5317f37e48 ("backlight: Add Kinetic KTD253 backlight driver")
Cc: Stephan Gerhold <stephan@gerhold.net>
Reported-by: newbyte@disroot.org
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
229 lines
6.3 KiB
C
229 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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ret = PTR_ERR(ktd253->gpiod);
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if (ret != -EPROBE_DEFER)
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dev_err(dev, "gpio line missing or invalid.\n");
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return ret;
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}
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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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