The Kinetic KTD253 backlight driver is controlled with a
single GPIO line, but still supports a range of brightness
settings by sending fast pulses on the line.
This is based off the source code release for the Samsung
GT-S7710 mobile phone.
Cc: Sam Ravnborg <s...@ravnborg.org>
Signed-off-by: Linus Walleij <linus.wall...@linaro.org>
---
ChangeLog v1->v2:
- Expose the 32 actual hardware levels of brightness directly
instead of using an interpolated "brightness" table.
- Use the new backlight_get_brightness() helper.
- Call backlight_update_status() in probe instead of calling
local functions to sync brightness.
- Sort includes alphabetically.
- Name the GPIO line "enable" and grab that in accordance
with the change to the DT bindings.
---
MAINTAINERS | 6 +
drivers/video/backlight/Kconfig | 8 +
drivers/video/backlight/Makefile | 1 +
drivers/video/backlight/ktd253-backlight.c | 198 +++++++++++++++++++++
4 files changed, 213 insertions(+)
create mode 100644 drivers/video/backlight/ktd253-backlight.c
diff --git a/MAINTAINERS b/MAINTAINERS
index e627ed60d75a..4c93e3a7be11 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9711,6 +9711,12 @@ F: Documentation/admin-guide/auxdisplay/ks0108.rst
F: drivers/auxdisplay/ks0108.c
F: include/linux/ks0108.h
+KTD253 BACKLIGHT DRIVER
+M: Linus Walleij <linus.wall...@linaro.org>
+S: Maintained
+F: Documentation/devicetree/bindings/leds/backlight/kinetic,ktd253.yaml
+F: drivers/video/backlight/ktd253-backlight.c
+
L3MDEV
M: David Ahern <dsah...@kernel.org>
L: net...@vger.kernel.org
diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index 87f9fc238d28..d83c87b902c1 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -182,6 +182,14 @@ config BACKLIGHT_IPAQ_MICRO
computers. Say yes if you have one of the h3100/h3600/h3700
machines.
+config BACKLIGHT_KTD253
+ tristate "Backlight Driver for Kinetic KTD253"
+ depends on GPIOLIB || COMPILE_TEST
+ help
+ Say y to enabled the backlight driver for the Kinetic KTD253
+ which is a 1-wire GPIO-controlled backlight found in some mobile
+ phones.
+
config BACKLIGHT_LM3533
tristate "Backlight Driver for LM3533"
depends on MFD_LM3533
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index 13463b99f1f9..685f3f1ca4df 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_BACKLIGHT_GPIO) += gpio_backlight.o
obj-$(CONFIG_BACKLIGHT_HP680) += hp680_bl.o
obj-$(CONFIG_BACKLIGHT_HP700) += jornada720_bl.o
obj-$(CONFIG_BACKLIGHT_IPAQ_MICRO) += ipaq_micro_bl.o
+obj-$(CONFIG_BACKLIGHT_KTD253) += ktd253-backlight.o
obj-$(CONFIG_BACKLIGHT_LM3533) += lm3533_bl.o
obj-$(CONFIG_BACKLIGHT_LM3630A) += lm3630a_bl.o
obj-$(CONFIG_BACKLIGHT_LM3639) += lm3639_bl.o
diff --git a/drivers/video/backlight/ktd253-backlight.c
b/drivers/video/backlight/ktd253-backlight.c
new file mode 100644
index 000000000000..e3fee3f1f582
--- /dev/null
+++ b/drivers/video/backlight/ktd253-backlight.c
@@ -0,0 +1,198 @@
+// 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.phill...@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_MS 3
+
+struct ktd253_backlight {
+ struct device *dev;
+ struct backlight_device *bl;
+ struct gpio_desc *gpiod;
+ u16 ratio;
+};
+
+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;
+ unsigned long flags;
+
+ 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) {
+ gpiod_set_value_cansleep(ktd253->gpiod, 1);
+ ndelay(KTD253_T_HIGH_NS);
+ /* We always fall back to this when we power on */
+ current_ratio = KTD253_MAX_RATIO;
+ }
+
+ /*
+ * WARNING:
+ * The loop to set the correct current level is performed
+ * with interrupts disabled as it is timing critical.
+ * The maximum number of cycles of the loop is 32
+ * so the time taken will be (T_LOW_NS + T_HIGH_NS + loop_time) * 32,
+ */
+ local_irq_save(flags);
+ 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!
+ */
+ gpiod_set_value(ktd253->gpiod, 0);
+ ndelay(KTD253_T_LOW_NS);
+ gpiod_set_value(ktd253->gpiod, 1);
+ ndelay(KTD253_T_HIGH_NS);
+ /* After 1/32 we loop back to 32/32 */
+ if (current_ratio == KTD253_MIN_RATIO)
+ current_ratio = KTD253_MAX_RATIO;
+ else
+ current_ratio--;
+ }
+ local_irq_restore(flags);
+ 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.wall...@linaro.org>");
+MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ktd253-backlight");
--
2.26.2
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