--- /dev/null
+// 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");
projects / thirdparty / linux.git / commitdiff
