From: Petri Karhula <petri.karhula@novatron.fi>

This driver provides backlight brightness control through the Linux
backlight subsystem. It communicates with the board controller to
adjust LCD backlight using PWM signals. Communication is done
through Congatec Board Controller core driver.

Signed-off-by: Petri Karhula <petri.karhula@novatron.fi>
---
 drivers/video/backlight/Kconfig   |  11 +++
 drivers/video/backlight/Makefile  |   1 +
 drivers/video/backlight/cgbc_bl.c | 179 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 191 insertions(+)

diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index d9374d208cee..702f3b8ed036 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -249,6 +249,17 @@ config BACKLIGHT_PWM
 	  If you have a LCD backlight adjustable by PWM, say Y to enable
 	  this driver.
 
+config BACKLIGHT_CGBC
+	tristate "Congatec Board Controller (CGBC) backlight support"
+	depends on MFD_CGBC && X86
+	help
+	  Say Y here to enable support for LCD backlight control on Congatec
+	  x86-based boards via the CGBC (Congatec Board Controller).
+
+	  This driver provides backlight brightness control through the Linux
+	  backlight subsystem. It communicates with the board controller to
+	  adjust LCD backlight using PWM signals.
+
 config BACKLIGHT_DA903X
 	tristate "Backlight Driver for DA9030/DA9034 using WLED"
 	depends on PMIC_DA903X
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index dfbb169bf6ea..0169fd8873ed 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -27,6 +27,7 @@ obj-$(CONFIG_BACKLIGHT_APPLE_DWI)	+= apple_dwi_bl.o
 obj-$(CONFIG_BACKLIGHT_AS3711)		+= as3711_bl.o
 obj-$(CONFIG_BACKLIGHT_BD6107)		+= bd6107.o
 obj-$(CONFIG_BACKLIGHT_CLASS_DEVICE)	+= backlight.o
+obj-$(CONFIG_BACKLIGHT_CGBC)		+= cgbc_bl.o
 obj-$(CONFIG_BACKLIGHT_DA903X)		+= da903x_bl.o
 obj-$(CONFIG_BACKLIGHT_DA9052)		+= da9052_bl.o
 obj-$(CONFIG_BACKLIGHT_EP93XX)		+= ep93xx_bl.o
diff --git a/drivers/video/backlight/cgbc_bl.c b/drivers/video/backlight/cgbc_bl.c
new file mode 100644
index 000000000000..74f80222d789
--- /dev/null
+++ b/drivers/video/backlight/cgbc_bl.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Congatec Board Controller (CGBC) Backlight Driver
+ *
+ * This driver provides backlight control for LCD displays connected to
+ * Congatec boards via the CGBC (Congatec Board Controller). It integrates
+ * with the Linux backlight subsystem and communicates with hardware through
+ * the cgbc-core module.
+ *
+ * Copyright (C) 2025 Novatron Oy
+ *
+ * Author: Petri Karhula <petri.karhula@novatron.fi>
+ */
+
+#include <linux/backlight.h>
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/mfd/cgbc.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#define BLT_PWM_DUTY_MASK          GENMASK(6, 0)
+
+/* CGBC command for PWM brightness control*/
+#define CGBC_CMD_BLT0_PWM          0x75
+
+#define CGBC_BL_MAX_BRIGHTNESS     100
+
+/**
+ * CGBC backlight driver data
+ * @dev: Pointer to the platform device
+ * @cgbc: Pointer to the parent CGBC device data
+ * @current_brightness: Current brightness level (0-100)
+ */
+struct cgbc_bl_data {
+	struct device *dev;
+	struct cgbc_device_data *cgbc;
+	unsigned int current_brightness;
+};
+
+static int cgbc_bl_read_brightness(struct cgbc_bl_data *bl_data)
+{
+	u8 cmd_buf[4] = { CGBC_CMD_BLT0_PWM };
+	u8 reply_buf[3];
+	int ret;
+
+	ret = cgbc_command(bl_data->cgbc, cmd_buf, sizeof(cmd_buf),
+			   reply_buf, sizeof(reply_buf), NULL);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Get only PWM duty factor percentage,
+	 * ignore polarity inversion bit (bit 7)
+	 */
+	bl_data->current_brightness = FIELD_GET(BLT_PWM_DUTY_MASK, reply_buf[0]);
+
+	return 0;
+}
+
+static int cgbc_bl_update_status(struct backlight_device *bl)
+{
+	struct cgbc_bl_data *bl_data = bl_get_data(bl);
+	u8 cmd_buf[4] = { CGBC_CMD_BLT0_PWM };
+	u8 reply_buf[3];
+	u8 brightness;
+	int ret;
+
+	brightness = backlight_get_brightness(bl);
+
+	if (brightness != bl_data->current_brightness) {
+		/* Read the current values */
+		ret = cgbc_command(bl_data->cgbc, cmd_buf, sizeof(cmd_buf), reply_buf,
+				   sizeof(reply_buf), NULL);
+		if (ret < 0) {
+			dev_err(bl_data->dev, "Failed to read PWM settings: %d\n", ret);
+			return ret;
+		}
+
+		/*
+		 * Prepare command buffer for writing new settings. Only 2nd byte is changed
+		 * to set new brightness (PWM duty cycle %). Other values (polarity, frequency)
+		 * are preserved from the read values.
+		 */
+		cmd_buf[1] = (reply_buf[0] & ~BLT_PWM_DUTY_MASK) |
+			FIELD_PREP(BLT_PWM_DUTY_MASK, brightness);
+		cmd_buf[2] = reply_buf[1];
+		cmd_buf[3] = reply_buf[2];
+
+		ret = cgbc_command(bl_data->cgbc, cmd_buf, sizeof(cmd_buf), reply_buf,
+				   sizeof(reply_buf), NULL);
+		if (ret < 0) {
+			dev_err(bl_data->dev, "Failed to set brightness: %d\n", ret);
+			return ret;
+		}
+
+		bl_data->current_brightness = reply_buf[0] & BLT_PWM_DUTY_MASK;
+
+		/* Verify the setting was applied correctly */
+		if (bl_data->current_brightness != brightness) {
+			dev_err(bl_data->dev,
+				"Brightness setting verification failed\n");
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+static int cgbc_bl_get_brightness(struct backlight_device *bl)
+{
+	struct cgbc_bl_data *bl_data = bl_get_data(bl);
+	int ret;
+
+	ret = cgbc_bl_read_brightness(bl_data);
+	if (ret < 0) {
+		dev_err(bl_data->dev, "Failed to read brightness: %d\n", ret);
+		return ret;
+	}
+
+	return bl_data->current_brightness;
+}
+
+static const struct backlight_ops cgbc_bl_ops = {
+	.options = BL_CORE_SUSPENDRESUME,
+	.update_status = cgbc_bl_update_status,
+	.get_brightness = cgbc_bl_get_brightness,
+};
+
+static int cgbc_bl_probe(struct platform_device *pdev)
+{
+	struct cgbc_device_data *cgbc = dev_get_drvdata(pdev->dev.parent);
+	struct backlight_properties props = { };
+	struct backlight_device *bl_dev;
+	struct cgbc_bl_data *bl_data;
+	int ret;
+
+	bl_data = devm_kzalloc(&pdev->dev, sizeof(*bl_data), GFP_KERNEL);
+	if (!bl_data)
+		return -ENOMEM;
+
+	bl_data->dev = &pdev->dev;
+	bl_data->cgbc = cgbc;
+
+	ret = cgbc_bl_read_brightness(bl_data);
+	if (ret < 0)
+		return dev_err_probe(&pdev->dev, ret,
+				     "Failed to read initial brightness\n");
+
+	props.type = BACKLIGHT_PLATFORM;
+	props.max_brightness = CGBC_BL_MAX_BRIGHTNESS;
+	props.brightness = bl_data->current_brightness;
+	props.scale = BACKLIGHT_SCALE_LINEAR;
+
+	bl_dev = devm_backlight_device_register(&pdev->dev, "cgbc-backlight",
+						&pdev->dev, bl_data,
+						&cgbc_bl_ops, &props);
+	if (IS_ERR(bl_dev))
+		return dev_err_probe(&pdev->dev, PTR_ERR(bl_dev),
+			     "Failed to register backlight device\n");
+
+	platform_set_drvdata(pdev, bl_data);
+
+	return 0;
+}
+
+static struct platform_driver cgbc_bl_driver = {
+	.driver = {
+		.name = "cgbc-backlight",
+	},
+	.probe = cgbc_bl_probe,
+};
+
+module_platform_driver(cgbc_bl_driver);
+
+MODULE_AUTHOR("Petri Karhula <petri.karhula@novatron.fi>");
+MODULE_DESCRIPTION("Congatec Board Controller (CGBC) Backlight Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:cgbc-backlight");

-- 
2.34.1

On 11/27/25 4:21 PM, Petri Karhula via B4 Relay wrote:
> From: Petri Karhula <petri.karhula@novatron.fi>
> 
> This driver provides backlight brightness control through the Linux
> backlight subsystem. It communicates with the board controller to
> adjust LCD backlight using PWM signals. Communication is done
> through Congatec Board Controller core driver.
Tested on a conga-SA7 module with conga-SEVAL carrier board.

Tested-by: Thomas Richard <thomas.richard@bootlin.com>

Best Regards,
Thomas

On 11/27/25 4:21 PM, Petri Karhula via B4 Relay wrote:
> From: Petri Karhula <petri.karhula@novatron.fi>
> 
> This driver provides backlight brightness control through the Linux
> backlight subsystem. It communicates with the board controller to
> adjust LCD backlight using PWM signals. Communication is done
> through Congatec Board Controller core driver.
> 

[...]

> +		bl_data->current_brightness = reply_buf[0] & BLT_PWM_DUTY_MASK;
> +
> +		/* Verify the setting was applied correctly */
> +		if (bl_data->current_brightness != brightness) {
> +			dev_err(bl_data->dev,
> +				"Brightness setting verification failed\n");
> +			return -EIO;
> +		}

I'm still not really convinced by other error messages, but okay let's
keep them. Maybe add current and requested brightnesses in this message,
it could be useful for debugging.

	"Brightness setting verification failed (X instead of Y)"

Otherwise looks good to me. I will test your series

Reviewed-by: Thomas Richard <thomas.richard@bootlin.com>

Best Regards,
Thomas

On Thu, Nov 27, 2025 at 03:21:59PM +0000, Petri Karhula via B4 Relay wrote:
> From: Petri Karhula <petri.karhula@novatron.fi>
>
> This driver provides backlight brightness control through the Linux
> backlight subsystem. It communicates with the board controller to
> adjust LCD backlight using PWM signals. Communication is done
> through Congatec Board Controller core driver.
>
> Signed-off-by: Petri Karhula <petri.karhula@novatron.fi>

Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org>


Daniel.