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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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