* [PATCH v2 1/2] dt-bindings: backlight: Add Orient Chip OCP8178
2026-08-12 19:21 [PATCH v2 0/2] backlight: Add support for Orient Chip OCP8178 Wim de With
@ 2026-08-12 19:21 ` Wim de With
2026-08-12 19:28 ` sashiko-bot
2026-08-12 19:21 ` [PATCH v2 2/2] backlight: Add support for " Wim de With
1 sibling, 1 reply; 5+ messages in thread
From: Wim de With @ 2026-08-12 19:21 UTC (permalink / raw)
To: Wim de With, Lee Jones, Daniel Thompson, Jingoo Han, Pavel Machek,
Rob Herring, Krzysztof Kozlowski, Conor Dooley, Helge Deller
Cc: dri-devel, linux-leds, devicetree, linux-kernel, linux-fbdev
Add device tree bindings for the Orient Chip OCP8178 LED backlight
driver.
Signed-off-by: Wim de With <wf@dewith.io>
---
.../bindings/leds/backlight/ocs,ocp8178.yaml | 47 ++++++++++++++++++++++
MAINTAINERS | 5 +++
2 files changed, 52 insertions(+)
diff --git a/Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml b/Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml
new file mode 100644
index 0000000000000..57c44d3383b88
--- /dev/null
+++ b/Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml
@@ -0,0 +1,47 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/backlight/ocs,ocp8178.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Orient Chip OCP8178 backlight
+
+maintainers:
+ - Wim de With <wf@dewith.io>
+
+description:
+ The Orient Chip OCP8178 is a white LED backlight driver controlled by a single
+ GPIO line with a vendor-specific onewire protocol.
+
+allOf:
+ - $ref: common.yaml#
+
+properties:
+ compatible:
+ const: ocs,ocp8178
+
+ enable-gpios:
+ description: GPIO to use to enable/disable and dim the backlight.
+ maxItems: 1
+
+ default-brightness:
+ maximum: 31
+
+ max-brightness:
+ maximum: 31
+
+required:
+ - compatible
+ - enable-gpios
+
+additionalProperties: false
+
+examples:
+ - |
+ #include <dt-bindings/gpio/gpio.h>
+ backlight {
+ compatible = "ocs,ocp8178";
+ enable-gpios = <&gpio2 5 GPIO_ACTIVE_HIGH>;
+ default-brightness = <13>;
+ max-brightness = <31>;
+ };
diff --git a/MAINTAINERS b/MAINTAINERS
index cfee5d47b214d..3ca99d9c32ef1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -19678,6 +19678,11 @@ F: drivers/mfd/ocelot*
F: drivers/net/dsa/ocelot/ocelot_ext.c
F: include/linux/mfd/ocelot.h
+OCP8178 BACKLIGHT DRIVER
+M: Wim de With <wf@dewith.io>
+S: Maintained
+F: Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml
+
OCXL (Open Coherent Accelerator Processor Interface OpenCAPI) DRIVER
M: Mahesh J Salgaonkar <mahesh@linux.ibm.com>
R: Andrew Donnellan <andrew+kernel@donnellan.id.au>
--
2.55.0
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH v2 2/2] backlight: Add support for Orient Chip OCP8178
2026-08-12 19:21 [PATCH v2 0/2] backlight: Add support for Orient Chip OCP8178 Wim de With
2026-08-12 19:21 ` [PATCH v2 1/2] dt-bindings: backlight: Add " Wim de With
@ 2026-08-12 19:21 ` Wim de With
2026-08-12 19:34 ` sashiko-bot
1 sibling, 1 reply; 5+ messages in thread
From: Wim de With @ 2026-08-12 19:21 UTC (permalink / raw)
To: Wim de With, Lee Jones, Daniel Thompson, Jingoo Han, Pavel Machek,
Rob Herring, Krzysztof Kozlowski, Conor Dooley, Helge Deller
Cc: dri-devel, linux-leds, devicetree, linux-kernel, linux-fbdev
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 onewire protocol, which enables
setting static brightness levels without requiring a continuous PWM
signal from the host CPU. Note that while the vendor calls the protocol
1-Wire, it is not the 1-Wire protocol from Dallas Semiconductor as
implemented in drivers/w1.
Signed-off-by: Wim de With <wf@dewith.io>
---
MAINTAINERS | 1 +
drivers/video/backlight/Kconfig | 10 ++
drivers/video/backlight/Makefile | 1 +
drivers/video/backlight/ocp8178_bl.c | 235 +++++++++++++++++++++++++++++++++++
4 files changed, 247 insertions(+)
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 <wf@dewith.io>
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 <mahesh@linux.ibm.com>
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..bc48636ef64e4
--- /dev/null
+++ b/drivers/video/backlight/ocp8178_bl.c
@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Orient Chip OCP8178 Backlight Driver
+ *
+ * Copyright (C) 2026 Wim de With
+ *
+ * Author: Wim de With <wf@dewith.io>
+ */
+
+#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/platform_device.h>
+#include <linux/property.h>
+
+#define OCP8178_MAX_BRIGHTNESS 0x1F /* 5 bits */
+
+#define OCP8178_DEVICE_ADDRESS 0x72
+
+#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_US (50 * 1000)
+
+#define OCP8178_T_OFF_US (3 * 1000) /* 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(ocp8178->gpiod, 0);
+ fsleep(OCP8178_T_OFF_US);
+
+ 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);
+ udelay(OCP8178_1W_T_EOS_US);
+ gpiod_set_value(ocp8178->gpiod, 1);
+
+ local_irq_restore(flags);
+}
+
+static void ocp8178_bl_set_brightness(struct ocp8178_bl *ocp8178, u8 brightness)
+{
+ u8 data = 0;
+
+ /*
+ * We cannot set RFA (request for acknowledge) unless the GPIO pin is
+ * configured as open drain.
+ */
+ data |= FIELD_PREP(OCP8178_DATA_RFA, 0);
+ 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);
+
+ 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");
+ if (gpiod_cansleep(ocp8178->gpiod))
+ return dev_err_probe(dev, -EINVAL,
+ "sleeping GPIO not supported\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;
+ fsleep(OCP8178_1W_INIT_SLEEP_US);
+ }
+ if (retries >= OCP8178_1W_INIT_MAX_RETRIES)
+ return dev_err_probe(dev, -ETIMEDOUT,
+ "failed to initialize onewire protocol\n");
+
+ 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_dbg(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 <wf@dewith.io>");
+MODULE_DESCRIPTION("Orient Chip OCP8178 Backlight Driver");
+MODULE_LICENSE("GPL");
--
2.55.0
^ permalink raw reply related [flat|nested] 5+ messages in thread