drivers/video/backlight/cgbc_bl.c

// 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");