Add a driver for the Orient Chip OCP8178 backlight controller. The OCP8178 supports either PWM or a vendor-specific onewire protocol over GPIO. This driver implements the single-wire protocol, which enables setting static brightness levels without requiring a continuous PWM signal from the host CPU.
Signed-off-by: Wim de With <[email protected]> --- MAINTAINERS | 1 + drivers/video/backlight/Kconfig | 10 ++ drivers/video/backlight/Makefile | 1 + drivers/video/backlight/ocp8178_bl.c | 243 +++++++++++++++++++++++++++ 4 files changed, 255 insertions(+) create mode 100644 drivers/video/backlight/ocp8178_bl.c diff --git a/MAINTAINERS b/MAINTAINERS index 3ca99d9c32ef1..7146e4dea8d78 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -19682,6 +19682,7 @@ OCP8178 BACKLIGHT DRIVER M: Wim de With <[email protected]> S: Maintained F: Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml +F: drivers/video/backlight/ocp8178_bl.c OCXL (Open Coherent Accelerator Processor Interface OpenCAPI) DRIVER M: Mahesh J Salgaonkar <[email protected]> diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig index 7aa1c4b21111f..aa845230c5f58 100644 --- a/drivers/video/backlight/Kconfig +++ b/drivers/video/backlight/Kconfig @@ -226,6 +226,16 @@ config BACKLIGHT_LOCOMO If you have a Sharp Zaurus SL-5500 (Collie) or SL-5600 (Poodle) say y to enable the LCD/backlight driver. +config BACKLIGHT_OCP8178 + tristate "OCP8178 Backlight Driver" + depends on GPIOLIB + help + If you have an Orient Chip OCP8178, say Y to enable the backlight + driver. + + To compile this driver as a module, choose M here: the module will + be called ocp8178_bl. + config BACKLIGHT_OMAP1 tristate "OMAP1 PWL-based LCD Backlight" depends on ARCH_OMAP1 || COMPILE_TEST diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile index 21c8313cfb121..c4e87b708ae21 100644 --- a/drivers/video/backlight/Makefile +++ b/drivers/video/backlight/Makefile @@ -51,6 +51,7 @@ obj-$(CONFIG_BACKLIGHT_MAX25014) += max25014.o obj-$(CONFIG_BACKLIGHT_MAX8925) += max8925_bl.o obj-$(CONFIG_BACKLIGHT_MP3309C) += mp3309c.o obj-$(CONFIG_BACKLIGHT_MT6370) += mt6370-backlight.o +obj-$(CONFIG_BACKLIGHT_OCP8178) += ocp8178_bl.o obj-$(CONFIG_BACKLIGHT_OMAP1) += omap1_bl.o obj-$(CONFIG_BACKLIGHT_PANDORA) += pandora_bl.o obj-$(CONFIG_BACKLIGHT_PWM) += pwm_bl.o diff --git a/drivers/video/backlight/ocp8178_bl.c b/drivers/video/backlight/ocp8178_bl.c new file mode 100644 index 0000000000000..4500c9d23f7ef --- /dev/null +++ b/drivers/video/backlight/ocp8178_bl.c @@ -0,0 +1,243 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Orient Chip OCP8178 Backlight Driver + * + * Copyright (C) 2026 Wim de With + * + * Author: Wim de With <[email protected]> + */ + +#include <linux/backlight.h> +#include <linux/bitfield.h> +#include <linux/bits.h> +#include <linux/delay.h> +#include <linux/device.h> +#include <linux/gpio/consumer.h> +#include <linux/irqflags.h> +#include <linux/mod_devicetable.h> +#include <linux/platform_device.h> +#include <linux/property.h> + +#define OCP8178_MAX_BRIGHTNESS 0x1F /* 5 bits */ + +#define OCP8178_DEVICE_ADDRESS 0x72 + +/* + * We cannot set RFA (request for acknowledge) unless the GPIO pin is + * configured as open drain. + */ +#define OCP8178_DATA_RFA BIT(7) +#define OCP8178_DATA_ADDR GENMASK(6, 5) +#define OCP8178_DATA_VALUE GENMASK(4, 0) + +#define OCP8178_1W_INIT_MAX_RETRIES 5 +#define OCP8178_1W_INIT_SLEEP_MS 50 + +#define OCP8178_T_OFF_MS 3 /* datasheet specifies at least 2.5 ms */ +#define OCP8178_1W_T_DELAY_US (100 + 10) /* 10 us as safety factor */ +#define OCP8178_1W_T_DETECT_US (260 + 10) /* 10 us as safety factor */ +#define OCP8178_1W_T_START_US 2 +#define OCP8178_1W_T_EOS_US 2 +#define OCP8178_1W_T_WIN_NS (1000 * 1000) + +/* + * The datasheet specifies 1.7 Kbps to 160 Kbps. + * 1 / (160 Kbps) is about 6.67 us, so using 7 us per bit should be fine. + * T_HIGH + T_LOW = 7 us + * T_HIGH > 2 * T_LOW for high bits + * T_LOW > 2 * T_HIGH for low bits + */ +#define OCP8178_1W_HIGH_BIT_T_LOW_US 2 +#define OCP8178_1W_HIGH_BIT_T_HIGH_US 5 +#define OCP8178_1W_LOW_BIT_T_LOW_US 5 +#define OCP8178_1W_LOW_BIT_T_HIGH_US 2 + +struct ocp8178_bl { + struct device *dev; + struct gpio_desc *gpiod; +}; + +static int ocp8178_bl_enable_onewire(struct ocp8178_bl *ocp8178) +{ + u64 start, duration; + + dev_dbg(ocp8178->dev, "enabling onewire protocol\n"); + + gpiod_set_value_cansleep(ocp8178->gpiod, 0); + msleep(OCP8178_T_OFF_MS); + + start = ktime_get_ns(); + + gpiod_set_value(ocp8178->gpiod, 1); + udelay(OCP8178_1W_T_DELAY_US); + gpiod_set_value(ocp8178->gpiod, 0); + udelay(OCP8178_1W_T_DETECT_US); + gpiod_set_value(ocp8178->gpiod, 1); + + duration = ktime_get_ns() - start; + + if (duration >= OCP8178_1W_T_WIN_NS) { + dev_err(ocp8178->dev, + "onewire detection window exceeded (%llu ns)\n", + duration); + return -EAGAIN; + } + + return 0; +} + +static void ocp8178_bl_write_u8(struct ocp8178_bl *ocp8178, u8 value) +{ + unsigned long flags; + + gpiod_set_value(ocp8178->gpiod, 1); + udelay(OCP8178_1W_T_START_US); + + local_irq_save(flags); + + for (int i = 7; i >= 0; i--) { + if ((value >> i) & 1) { + gpiod_set_value(ocp8178->gpiod, 0); + udelay(OCP8178_1W_HIGH_BIT_T_LOW_US); + gpiod_set_value(ocp8178->gpiod, 1); + udelay(OCP8178_1W_HIGH_BIT_T_HIGH_US); + } else { + gpiod_set_value(ocp8178->gpiod, 0); + udelay(OCP8178_1W_LOW_BIT_T_LOW_US); + gpiod_set_value(ocp8178->gpiod, 1); + udelay(OCP8178_1W_LOW_BIT_T_HIGH_US); + } + } + + gpiod_set_value(ocp8178->gpiod, 0); + + local_irq_restore(flags); + + udelay(OCP8178_1W_T_EOS_US); + gpiod_set_value(ocp8178->gpiod, 1); +} + +static void ocp8178_bl_set_brightness(struct ocp8178_bl *ocp8178, u8 brightness) +{ + u8 data = 0; + + dev_dbg(ocp8178->dev, "setting brightness to %u\n", brightness); + + data |= FIELD_PREP(OCP8178_DATA_ADDR, 0); + data |= FIELD_PREP(OCP8178_DATA_VALUE, brightness); + + ocp8178_bl_write_u8(ocp8178, OCP8178_DEVICE_ADDRESS); + ocp8178_bl_write_u8(ocp8178, data); +} + +static int ocp8178_bl_update_status(struct backlight_device *bl) +{ + struct ocp8178_bl *ocp8178 = bl_get_data(bl); + u8 brightness = backlight_get_brightness(bl); + + /* + * Setting brightness to 0 turns the backlight off but retains the + * onewire mode. If we disable the controller, we would need to enable + * the onewire mode again. + */ + if (backlight_is_blank(bl)) + brightness = 0; + + ocp8178_bl_set_brightness(ocp8178, brightness); + return 0; +} + +static const struct backlight_ops ocp8178_bl_ops = { + .options = BL_CORE_SUSPENDRESUME, + .update_status = ocp8178_bl_update_status, +}; + +static int ocp8178_bl_probe(struct platform_device *pdev) +{ + struct device *dev = &pdev->dev; + struct backlight_device *bl; + struct backlight_properties props; + struct ocp8178_bl *ocp8178; + u32 max_brightness, brightness; + int ret, retries; + + ocp8178 = devm_kzalloc(dev, sizeof(*ocp8178), GFP_KERNEL); + if (!ocp8178) + return -ENOMEM; + + ocp8178->dev = dev; + + ret = device_property_read_u32(dev, "max-brightness", &max_brightness); + if (ret) + max_brightness = OCP8178_MAX_BRIGHTNESS; + if (max_brightness > OCP8178_MAX_BRIGHTNESS) { + dev_warn(dev, "max brightness exceeds hardware limit\n"); + max_brightness = OCP8178_MAX_BRIGHTNESS; + } + + ret = device_property_read_u32(dev, "default-brightness", &brightness); + if (ret) + brightness = max_brightness; + if (brightness > max_brightness) { + dev_warn(dev, "default brightness exceeds max brightness\n"); + brightness = max_brightness; + } + + ocp8178->gpiod = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW); + if (IS_ERR(ocp8178->gpiod)) + return dev_err_probe(dev, PTR_ERR(ocp8178->gpiod), + "gpio missing or invalid\n"); + gpiod_set_consumer_name(ocp8178->gpiod, dev_name(dev)); + + for (retries = 0; retries < OCP8178_1W_INIT_MAX_RETRIES; retries++) { + ret = ocp8178_bl_enable_onewire(ocp8178); + if (!ret) + break; + if (ret != -EAGAIN) + return ret; + msleep(OCP8178_1W_INIT_SLEEP_MS); + } + if (retries >= OCP8178_1W_INIT_MAX_RETRIES) + return dev_err_probe(dev, -ETIMEDOUT, + "failed to initialize onewire protocol"); + + props = (typeof(props)){ + .type = BACKLIGHT_RAW, + .brightness = brightness, + .max_brightness = max_brightness, + .power = BACKLIGHT_POWER_ON, + .scale = BACKLIGHT_SCALE_NON_LINEAR, + }; + + bl = devm_backlight_device_register(dev, dev_name(dev), dev, ocp8178, + &ocp8178_bl_ops, &props); + if (IS_ERR(bl)) + return dev_err_probe(dev, PTR_ERR(bl), + "failed to register backlight\n"); + + platform_set_drvdata(pdev, bl); + backlight_update_status(bl); + + dev_info(dev, "probed, brightness=%u/%u\n", brightness, max_brightness); + + return 0; +} + +static const struct of_device_id ocp8178_bl_of_match[] = { + { .compatible = "ocs,ocp8178" }, + { /* sentinel */ } +}; +MODULE_DEVICE_TABLE(of, ocp8178_bl_of_match); + +static struct platform_driver ocp8178_bl_driver = { + .driver = { + .name = "ocp8178-bl", + .of_match_table = ocp8178_bl_of_match, + }, + .probe = ocp8178_bl_probe, +}; +module_platform_driver(ocp8178_bl_driver); + +MODULE_AUTHOR("Wim de With <[email protected]>"); +MODULE_DESCRIPTION("Orient Chip OCP8178 Backlight Driver"); +MODULE_LICENSE("GPL"); -- 2.55.0
