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petri-klag-linaro
petri-k
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backlight: Add Congatec Board Controller (CGBC) backlight support
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-by: Thomas Richard <thomas.richard@bootlin.com> Reviewed-by: Thomas Richard <thomas.richard@bootlin.com> Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org> Signed-off-by: Petri Karhula <petri.karhula@novatron.fi> Link: https://patch.msgid.link/20251205-cgbc-backlight-v6-1-e4175b0bf406@novatron.fi Signed-off-by: Lee Jones <lee@kernel.org>
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‎drivers/video/backlight/Kconfig‎

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@@ -258,6 +258,17 @@ config BACKLIGHT_PWM
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If you have a LCD backlight adjustable by PWM, say Y to enable
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this driver.
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config BACKLIGHT_CGBC
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tristate "Congatec Board Controller (CGBC) backlight support"
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depends on MFD_CGBC && X86
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help
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Say Y here to enable support for LCD backlight control on Congatec
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x86-based boards via the CGBC (Congatec Board Controller).
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This driver provides backlight brightness control through the Linux
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backlight subsystem. It communicates with the board controller to
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adjust LCD backlight using PWM signals.
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config BACKLIGHT_DA903X
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tristate "Backlight Driver for DA9030/DA9034 using WLED"
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depends on PMIC_DA903X

‎drivers/video/backlight/Makefile‎

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@@ -27,6 +27,7 @@ obj-$(CONFIG_BACKLIGHT_APPLE_DWI) += apple_dwi_bl.o
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obj-$(CONFIG_BACKLIGHT_AS3711) += as3711_bl.o
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obj-$(CONFIG_BACKLIGHT_AW99706) += aw99706.o
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obj-$(CONFIG_BACKLIGHT_BD6107) += bd6107.o
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obj-$(CONFIG_BACKLIGHT_CGBC) += cgbc_bl.o
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obj-$(CONFIG_BACKLIGHT_CLASS_DEVICE) += backlight.o
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obj-$(CONFIG_BACKLIGHT_DA903X) += da903x_bl.o
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obj-$(CONFIG_BACKLIGHT_DA9052) += da9052_bl.o

‎drivers/video/backlight/cgbc_bl.c‎

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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Congatec Board Controller (CGBC) Backlight Driver
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*
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* This driver provides backlight control for LCD displays connected to
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* Congatec boards via the CGBC (Congatec Board Controller). It integrates
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* with the Linux backlight subsystem and communicates with hardware through
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* the cgbc-core module.
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*
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* Copyright (C) 2025 Novatron Oy
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*
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* Author: Petri Karhula <petri.karhula@novatron.fi>
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*/
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#include <linux/backlight.h>
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#include <linux/bitfield.h>
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#include <linux/bits.h>
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#include <linux/mfd/cgbc.h>
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#include <linux/module.h>
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#include <linux/platform_device.h>
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#define BLT_PWM_DUTY_MASK GENMASK(6, 0)
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/* CGBC command for PWM brightness control*/
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#define CGBC_CMD_BLT0_PWM 0x75
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#define CGBC_BL_MAX_BRIGHTNESS 100
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/**
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* CGBC backlight driver data
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* @dev: Pointer to the platform device
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* @cgbc: Pointer to the parent CGBC device data
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* @current_brightness: Current brightness level (0-100)
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*/
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struct cgbc_bl_data {
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struct device *dev;
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struct cgbc_device_data *cgbc;
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unsigned int current_brightness;
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};
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static int cgbc_bl_read_brightness(struct cgbc_bl_data *bl_data)
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{
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u8 cmd_buf[4] = { CGBC_CMD_BLT0_PWM };
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u8 reply_buf[3];
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int ret;
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ret = cgbc_command(bl_data->cgbc, cmd_buf, sizeof(cmd_buf),
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reply_buf, sizeof(reply_buf), NULL);
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if (ret < 0)
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return ret;
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/*
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* Get only PWM duty factor percentage,
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* ignore polarity inversion bit (bit 7)
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*/
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bl_data->current_brightness = FIELD_GET(BLT_PWM_DUTY_MASK, reply_buf[0]);
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return 0;
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}
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static int cgbc_bl_update_status(struct backlight_device *bl)
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{
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struct cgbc_bl_data *bl_data = bl_get_data(bl);
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u8 cmd_buf[4] = { CGBC_CMD_BLT0_PWM };
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u8 reply_buf[3];
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u8 brightness;
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int ret;
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brightness = backlight_get_brightness(bl);
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if (brightness != bl_data->current_brightness) {
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/* Read the current values */
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ret = cgbc_command(bl_data->cgbc, cmd_buf, sizeof(cmd_buf), reply_buf,
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sizeof(reply_buf), NULL);
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if (ret < 0) {
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dev_err(bl_data->dev, "Failed to read PWM settings: %d\n", ret);
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return ret;
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}
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/*
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* Prepare command buffer for writing new settings. Only 2nd byte is changed
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* to set new brightness (PWM duty cycle %). Other values (polarity, frequency)
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* are preserved from the read values.
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*/
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cmd_buf[1] = (reply_buf[0] & ~BLT_PWM_DUTY_MASK) |
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FIELD_PREP(BLT_PWM_DUTY_MASK, brightness);
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cmd_buf[2] = reply_buf[1];
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cmd_buf[3] = reply_buf[2];
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ret = cgbc_command(bl_data->cgbc, cmd_buf, sizeof(cmd_buf), reply_buf,
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sizeof(reply_buf), NULL);
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if (ret < 0) {
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dev_err(bl_data->dev, "Failed to set brightness: %d\n", ret);
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return ret;
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}
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bl_data->current_brightness = reply_buf[0] & BLT_PWM_DUTY_MASK;
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/* Verify the setting was applied correctly */
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if (bl_data->current_brightness != brightness) {
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dev_err(bl_data->dev,
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"Brightness setting verification failed (got %u, expected %u)\n",
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bl_data->current_brightness, (unsigned int)brightness);
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return -EIO;
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}
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}
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return 0;
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}
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static int cgbc_bl_get_brightness(struct backlight_device *bl)
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{
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struct cgbc_bl_data *bl_data = bl_get_data(bl);
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int ret;
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ret = cgbc_bl_read_brightness(bl_data);
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if (ret < 0) {
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dev_err(bl_data->dev, "Failed to read brightness: %d\n", ret);
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return ret;
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}
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return bl_data->current_brightness;
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}
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static const struct backlight_ops cgbc_bl_ops = {
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.options = BL_CORE_SUSPENDRESUME,
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.update_status = cgbc_bl_update_status,
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.get_brightness = cgbc_bl_get_brightness,
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};
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static int cgbc_bl_probe(struct platform_device *pdev)
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{
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struct cgbc_device_data *cgbc = dev_get_drvdata(pdev->dev.parent);
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struct backlight_properties props = { };
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struct backlight_device *bl_dev;
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struct cgbc_bl_data *bl_data;
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int ret;
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bl_data = devm_kzalloc(&pdev->dev, sizeof(*bl_data), GFP_KERNEL);
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if (!bl_data)
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return -ENOMEM;
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bl_data->dev = &pdev->dev;
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bl_data->cgbc = cgbc;
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ret = cgbc_bl_read_brightness(bl_data);
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if (ret < 0)
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return dev_err_probe(&pdev->dev, ret,
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"Failed to read initial brightness\n");
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props.type = BACKLIGHT_PLATFORM;
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props.max_brightness = CGBC_BL_MAX_BRIGHTNESS;
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props.brightness = bl_data->current_brightness;
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props.scale = BACKLIGHT_SCALE_LINEAR;
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bl_dev = devm_backlight_device_register(&pdev->dev, "cgbc-backlight",
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&pdev->dev, bl_data,
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&cgbc_bl_ops, &props);
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if (IS_ERR(bl_dev))
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return dev_err_probe(&pdev->dev, PTR_ERR(bl_dev),
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"Failed to register backlight device\n");
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platform_set_drvdata(pdev, bl_data);
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return 0;
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}
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static struct platform_driver cgbc_bl_driver = {
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.driver = {
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.name = "cgbc-backlight",
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},
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.probe = cgbc_bl_probe,
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};
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module_platform_driver(cgbc_bl_driver);
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MODULE_AUTHOR("Petri Karhula <petri.karhula@novatron.fi>");
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MODULE_DESCRIPTION("Congatec Board Controller (CGBC) Backlight Driver");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("platform:cgbc-backlight");

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