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

[PATCH 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

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

 .../bindings/leds/backlight/ocs,ocp8178.yaml  |  46 ++++
 MAINTAINERS                                   |   6 +
 drivers/video/backlight/Kconfig               |  10 +
 drivers/video/backlight/Makefile              |   1 +
 drivers/video/backlight/ocp8178_bl.c          | 243 ++++++++++++++++++
 5 files changed, 306 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml
 create mode 100644 drivers/video/backlight/ocp8178_bl.c

-- 
2.55.0

[PATCH 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  | 46 +++++++++++++++++++
 MAINTAINERS                                   |  5 ++
 2 files changed, 51 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml

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..9a4df1ef91edd
--- /dev/null
+++ b/Documentation/devicetree/bindings/leds/backlight/ocs,ocp8178.yaml
@@ -0,0 +1,46 @@
+# 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 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 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 <wf@dewith.io>
---
 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 <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..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 <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/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 <wf@dewith.io>");
+MODULE_DESCRIPTION("Orient Chip OCP8178 Backlight Driver");
+MODULE_LICENSE("GPL");
-- 
2.55.0