[PATCH v2 0/2] backlight: Add support for Orient Chip OCP8178

[PATCH v2 0/2] backlight: Add support for Orient Chip OCP8178

[Wim de With]

The ClockworkPi uConsole[1] is a modular handheld console manufactured
by Clockwork Tech that runs Linux. It consists of a mainboard which
connects a number of peripherals, such as the screen, batteries and
keyboard. This mainboard hosts a system on a module (SoM), such as the
Raspberry Pi Compute Module as a so-called core to provide the compute
for the device. The device supports different kinds of SoM as cores. The
mainboard is shared between different devices, such as the DevTerm[2].

Currently, the uConsole requires a number of out-of-tree drivers to
support the hardware. In addition, most (if not all) supported SoMs
require vendor kernels. In practice, this means that kernel support for
the device is scattered across various repositories in the form of
patches with dubious quality.

This patch series is the first in an attempt to upstream as many of the
needed drivers as possible. The goal is to support at least the
mainboard and the peripherals of the uConsole in the upstream kernel.
These drivers should find their way downstream to the SoM vendor kernels
eventually.

This series adds the driver for the backlight controller, the Orient
Chip OCP8178. I wrote the driver from scratch using the datasheet, to
avoid any copyright or attribution problems.

[1]: https://www.clockworkpi.com/home-uconsole
[2]: https://www.clockworkpi.com/home-devterm

v2:
- Add a note in the commit message that the 1-Wire protocol is not the
  one implemented in drivers/w1
- Explicitly reject sleepable GPIO and don't use _cansleep() functions
- Fix bug where interrupts were restored during timing-critical section
- Remove unnecessary logging
- Add missing \n to dev_err_probe message
- Remove linux/mod_devicetable.h include
- Remove struct init padding
- Remove unnecessary backlight_is_blank() check
- Use appropriate delay functions
- Set RFA explicitly and move comment
- Format DT binding YAML

---
Wim de With (2):
      dt-bindings: backlight: Add Orient Chip OCP8178
      backlight: Add support for Orient Chip OCP8178

 .../bindings/leds/backlight/ocs,ocp8178.yaml       |  47 +++++
 MAINTAINERS                                        |   6 +
 drivers/video/backlight/Kconfig                    |  10 +
 drivers/video/backlight/Makefile                   |   1 +
 drivers/video/backlight/ocp8178_bl.c               | 235 +++++++++++++++++++++
 5 files changed, 299 insertions(+)
---
base-commit: 315f4bd234b3b8a3ed3a71fd4c53b110cf373720
change-id: 20260808-ocp8178-backlight-9ead3e930ef3

Best regards,
--  
Wim de With <wf@dewith.io>

[PATCH v2 1/2] dt-bindings: backlight: Add Orient Chip OCP8178

[Wim de With]

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

[PATCH v2 2/2] backlight: Add support for Orient Chip OCP8178

[Wim de With]

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

Re: [PATCH v2 1/2] dt-bindings: backlight: Add Orient Chip OCP8178

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The schema uses `additionalProperties: false` while also referencing `common.yaml#`, which will incorrectly reject standard inherited properties.
--

--- Patch [1]: [PATCH v2 1/2] dt-bindings: backlight: Add Orient Chip OCP8178 ---
commit e31a9b24875ae6868d7bab27e5c73b0f9db06347
Author: Wim de With <wf@dewith.io>

dt-bindings: backlight: Add Orient Chip OCP8178

This commit adds device tree bindings for the Orient Chip OCP8178 LED
backlight driver, introducing a new YAML schema.

> 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
[ ... ]
> +allOf:
> +  - $ref: common.yaml#
> +
> +properties:
[ ... ]
> +required:
> +  - compatible
> +  - enable-gpios
> +
> +additionalProperties: false

[Severity: Medium]
Since this schema references common.yaml, should this be set to
unevaluatedProperties: false instead? Using additionalProperties: false
will incorrectly reject legitimate properties inherited from common.yaml
during schema validation.

> +
> +examples:
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260812-ocp8178-backlight-v2-0-4ad18b48bef8@dewith.io?part=1

Re: [PATCH v2 2/2] backlight: Add support for Orient Chip OCP8178

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] The driver fails to re-initialize the 1-Wire mode after a power loss (e.g., during suspend), leaving the device stuck in PWM mode.
- [Medium] Lack of atomicity and timing validation across the 2-byte 1-Wire transaction can cause silent brightness update failures due to preemption.
--

--- Patch [2]: [PATCH v2 2/2] backlight: Add support for Orient Chip OCP8178 ---
commit 11ca2bd66a2c85f8bb56c8b3475708379c8ddf5e
Author: Wim de With <wf@dewith.io>

backlight: Add support for Orient Chip OCP8178

Add a driver for the Orient Chip OCP8178 backlight controller.
The OCP8178 supports either PWM or a vendor-specific onewire protocol
over GPIO.

> 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
[ ... ]
> +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);

[Severity: Medium]
Can a preemption or interrupt between these two byte writes delay the second
byte and violate the 1-Wire protocol timing?

The initialization sequence ocp8178_bl_enable_onewire() explicitly checks
duration >= OCP8178_1W_T_WIN_NS to verify that timing wasn't ruined by
preemption. However, in ocp8178_bl_set_brightness(), if the thread is preempted
between the two ocp8178_bl_write_u8() calls, the GPIO line is left idle HIGH.

Would this cause the hardware's 1-Wire state machine to time out and treat the
subsequent data byte as a new command, resulting in a silently lost brightness
update since the driver doesn't read an ACK?

> +}
[ ... ]
> +static const struct backlight_ops ocp8178_bl_ops = {
> +	.options = BL_CORE_SUSPENDRESUME,
> +	.update_status = ocp8178_bl_update_status,
> +};
[ ... ]
> +static struct platform_driver ocp8178_bl_driver = {
> +	.driver = {
> +		.name = "ocp8178-bl",
> +		.of_match_table = ocp8178_bl_of_match,
> +	},
> +	.probe = ocp8178_bl_probe,
> +};

[Severity: High]
Does this driver need a resume PM hook to re-initialize the 1-Wire mode?

The BL_CORE_SUSPENDRESUME option causes the backlight core to call
update_status() on resume. Since power to the chip may be cut during suspend,
the device defaults to PWM mode upon power-on.

Without a resume hook in the platform driver to call
ocp8178_bl_enable_onewire(), the chip will misinterpret the 1-Wire brightness
data as a PWM signal. This leaves the GPIO HIGH at the end of the transaction,
which translates to 100% brightness in PWM mode.

> +module_platform_driver(ocp8178_bl_driver);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260812-ocp8178-backlight-v2-0-4ad18b48bef8@dewith.io?part=2