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    Subject[PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver
    Add driver for the Kinetic KTD2801 backlight driver.

    Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>

    ---
    Shared ExpressWire handling code and preemption watchdogs haven't been
    implemented in this version as my questions regarding these two weren't
    answered.
    ---
    MAINTAINERS | 6 ++
    drivers/video/backlight/Kconfig | 7 ++
    drivers/video/backlight/Makefile | 1 +
    drivers/video/backlight/ktd2801-backlight.c | 149 ++++++++++++++++++++++++++++
    4 files changed, 163 insertions(+)

    diff --git a/MAINTAINERS b/MAINTAINERS
    index a7c4cf8201e0..1e25d760f312 100644
    --- a/MAINTAINERS
    +++ b/MAINTAINERS
    @@ -11884,6 +11884,12 @@ S: Maintained
    F: Documentation/devicetree/bindings/leds/backlight/kinetic,ktd253.yaml
    F: drivers/video/backlight/ktd253-backlight.c

    +KTD2801 BACKLIGHT DRIVER
    +M: Duje Mihanović <duje.mihanovic@skole.hr>
    +S: Maintained
    +F: Documentation/devicetree/bindings/leds/backlight/kinetic,ktd2801.yaml
    +F: drivers/video/backlight/ktd2801-backlight.c
    +
    KTEST
    M: Steven Rostedt <rostedt@goodmis.org>
    M: John Hawley <warthog9@eaglescrag.net>
    diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
    index 51387b1ef012..a2b268293345 100644
    --- a/drivers/video/backlight/Kconfig
    +++ b/drivers/video/backlight/Kconfig
    @@ -183,6 +183,13 @@ config BACKLIGHT_KTD253
    which is a 1-wire GPIO-controlled backlight found in some mobile
    phones.

    +config BACKLIGHT_KTD2801
    + tristate "Backlight Driver for Kinetic KTD2801"
    + depends on GPIOLIB || COMPILE_TEST
    + help
    + Say Y to enable the backlight driver for the Kinetic KTD2801 1-wire
    + GPIO-controlled backlight found in Samsung Galaxy Core Prime VE LTE.
    +
    config BACKLIGHT_KTZ8866
    tristate "Backlight Driver for Kinetic KTZ8866"
    depends on I2C
    diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
    index f72e1c3c59e9..b33b647f31ca 100644
    --- a/drivers/video/backlight/Makefile
    +++ b/drivers/video/backlight/Makefile
    @@ -35,6 +35,7 @@ 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-$(CONFIG_BACKLIGHT_KTD2801) += ktd2801-backlight.o
    obj-$(CONFIG_BACKLIGHT_KTZ8866) += ktz8866.o
    obj-$(CONFIG_BACKLIGHT_LM3533) += lm3533_bl.o
    obj-$(CONFIG_BACKLIGHT_LM3630A) += lm3630a_bl.o
    diff --git a/drivers/video/backlight/ktd2801-backlight.c b/drivers/video/backlight/ktd2801-backlight.c
    new file mode 100644
    index 000000000000..bbcb2e2059a2
    --- /dev/null
    +++ b/drivers/video/backlight/ktd2801-backlight.c
    @@ -0,0 +1,149 @@
    +// SPDX-License-Identifier: GPL-2.0-only
    +#include <linux/backlight.h>
    +#include <linux/delay.h>
    +#include <linux/gpio/consumer.h>
    +#include <linux/of.h>
    +#include <linux/platform_device.h>
    +#include <linux/property.h>
    +
    +/* These values have been extracted from Samsung's driver. */
    +#define KTD2801_EXPRESSWIRE_DETECT_DELAY_US 150
    +#define KTD2801_EXPRESSWIRE_DETECT_US 270
    +#define KTD2801_LOW_BIT_HIGH_TIME_US 5
    +#define KTD2801_LOW_BIT_LOW_TIME_US (4 * KTD2801_HIGH_BIT_LOW_TIME_US)
    +#define KTD2801_HIGH_BIT_LOW_TIME_US 5
    +#define KTD2801_HIGH_BIT_HIGH_TIME_US (4 * KTD2801_HIGH_BIT_LOW_TIME_US)
    +#define KTD2801_DATA_START_US 5
    +#define KTD2801_END_OF_DATA_LOW_US 10
    +#define KTD2801_END_OF_DATA_HIGH_US 350
    +#define KTD2801_PWR_DOWN_DELAY_US 2600
    +
    +#define KTD2801_DEFAULT_BRIGHTNESS 100
    +#define KTD2801_MAX_BRIGHTNESS 255
    +
    +struct ktd2801_backlight {
    + struct backlight_device *bd;
    + struct gpio_desc *gpiod;
    + bool was_on;
    +};
    +
    +static int ktd2801_update_status(struct backlight_device *bd)
    +{
    + struct ktd2801_backlight *ktd2801 = bl_get_data(bd);
    + u8 brightness = (u8) backlight_get_brightness(bd);
    +
    + if (backlight_is_blank(bd)) {
    + gpiod_set_value(ktd2801->gpiod, 0);
    + udelay(KTD2801_PWR_DOWN_DELAY_US);
    + ktd2801->was_on = false;
    + return 0;
    + }
    +
    + if (!ktd2801->was_on) {
    + gpiod_set_value(ktd2801->gpiod, 1);
    + udelay(KTD2801_EXPRESSWIRE_DETECT_DELAY_US);
    + gpiod_set_value(ktd2801->gpiod, 0);
    + udelay(KTD2801_EXPRESSWIRE_DETECT_US);
    + gpiod_set_value(ktd2801->gpiod, 1);
    + ktd2801->was_on = true;
    + }
    +
    + gpiod_set_value(ktd2801->gpiod, 1);
    + udelay(KTD2801_DATA_START_US);
    +
    + for (int i = 0; i < 8; i++) {
    + u8 next_bit = (brightness & 0x80) >> 7;
    +
    + if (!next_bit) {
    + gpiod_set_value(ktd2801->gpiod, 0);
    + udelay(KTD2801_LOW_BIT_LOW_TIME_US);
    + gpiod_set_value(ktd2801->gpiod, 1);
    + udelay(KTD2801_LOW_BIT_HIGH_TIME_US);
    + } else {
    + gpiod_set_value(ktd2801->gpiod, 0);
    + udelay(KTD2801_HIGH_BIT_LOW_TIME_US);
    + gpiod_set_value(ktd2801->gpiod, 1);
    + udelay(KTD2801_HIGH_BIT_HIGH_TIME_US);
    + }
    + brightness <<= 1;
    + }
    + gpiod_set_value(ktd2801->gpiod, 0);
    + udelay(KTD2801_END_OF_DATA_LOW_US);
    + gpiod_set_value(ktd2801->gpiod, 1);
    + udelay(KTD2801_END_OF_DATA_HIGH_US);
    + return 0;
    +}
    +
    +static const struct backlight_ops ktd2801_backlight_ops = {
    + .update_status = ktd2801_update_status,
    +};
    +
    +static int ktd2801_backlight_probe(struct platform_device *pdev)
    +{
    + struct device *dev = &pdev->dev;
    + struct backlight_device *bd;
    + struct ktd2801_backlight *ktd2801;
    + u32 brightness, max_brightness;
    + int ret;
    +
    + ktd2801 = devm_kzalloc(dev, sizeof(*ktd2801), GFP_KERNEL);
    + if (!ktd2801)
    + return -ENOMEM;
    + ktd2801->was_on = true;
    +
    + ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
    + if (ret)
    + max_brightness = KTD2801_MAX_BRIGHTNESS;
    + if (max_brightness > KTD2801_MAX_BRIGHTNESS) {
    + dev_err(dev, "illegal max brightness specified\n");
    + max_brightness = KTD2801_MAX_BRIGHTNESS;
    + }
    +
    + ret = device_property_read_u32(dev, "default-brightness", &brightness);
    + if (ret)
    + brightness = KTD2801_DEFAULT_BRIGHTNESS;
    + if (brightness > max_brightness) {
    + dev_err(dev, "default brightness exceeds max\n");
    + brightness = max_brightness;
    + }
    +
    + ktd2801->gpiod = devm_gpiod_get(dev, "ctrl", GPIOD_OUT_HIGH);
    + if (IS_ERR(ktd2801->gpiod))
    + return dev_err_probe(dev, PTR_ERR(dev),
    + "failed to get backlight GPIO");
    + gpiod_set_consumer_name(ktd2801->gpiod, dev_name(dev));
    +
    + bd = devm_backlight_device_register(dev, dev_name(dev), dev, ktd2801,
    + &ktd2801_backlight_ops, NULL);
    + if (IS_ERR(bd))
    + return dev_err_probe(dev, PTR_ERR(bd),
    + "failed to register backlight");
    +
    + bd->props.max_brightness = max_brightness;
    + bd->props.brightness = brightness;
    +
    + ktd2801->bd = bd;
    + platform_set_drvdata(pdev, bd);
    + backlight_update_status(bd);
    +
    + return 0;
    +}
    +
    +static const struct of_device_id ktd2801_of_match[] = {
    + { .compatible = "kinetic,ktd2801" },
    + { }
    +};
    +MODULE_DEVICE_TABLE(of, ktd2801_of_match);
    +
    +static struct platform_driver ktd2801_backlight_driver = {
    + .driver = {
    + .name = "ktd2801-backlight",
    + .of_match_table = ktd2801_of_match,
    + },
    + .probe = ktd2801_backlight_probe,
    +};
    +module_platform_driver(ktd2801_backlight_driver);
    +
    +MODULE_AUTHOR("Duje Mihanović <duje.mihanovic@skole.hr>");
    +MODULE_DESCRIPTION("Kinetic KTD2801 Backlight Driver");
    +MODULE_LICENSE("GPL");
    --
    2.43.0



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