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// 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 (got %u, expected %u)\n",
bl_data->current_brightness, (unsigned int)brightness);
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");
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