// SPDX-License-Identifier: GPL-2.0+
  /*
   * Raspberry Pi voltage sensor driver
   *
   * Based on firmware/raspberrypi.c by Noralf Trønnes
   *
   * Copyright (C) 2018 Stefan Wahren <stefan.wahren@i2se.com>
   */
  #include <linux/device.h>
  #include <linux/err.h>
  #include <linux/hwmon.h>
  #include <linux/module.h>
  #include <linux/platform_device.h>
  #include <linux/slab.h>
  #include <linux/workqueue.h>
  #include <soc/bcm2835/raspberrypi-firmware.h>
  
  #define UNDERVOLTAGE_STICKY_BIT	BIT(16)
  
  struct rpi_hwmon_data {
  	struct device *hwmon_dev;
  	struct rpi_firmware *fw;
  	u32 last_throttled;
  	struct delayed_work get_values_poll_work;
  };
  
  static void rpi_firmware_get_throttled(struct rpi_hwmon_data *data)
  {
  	u32 new_uv, old_uv, value;
  	int ret;
  
  	/* Request firmware to clear sticky bits */
  	value = 0xffff;
  
  	ret = rpi_firmware_property(data->fw, RPI_FIRMWARE_GET_THROTTLED,
  				    &value, sizeof(value));
  	if (ret) {
  		dev_err_once(data->hwmon_dev, "Failed to get throttled (%d)
  ",
  			     ret);
  		return;
  	}
  
  	new_uv = value & UNDERVOLTAGE_STICKY_BIT;
  	old_uv = data->last_throttled & UNDERVOLTAGE_STICKY_BIT;
  	data->last_throttled = value;
  
  	if (new_uv == old_uv)
  		return;
  
  	if (new_uv)
  		dev_crit(data->hwmon_dev, "Undervoltage detected!
  ");
  	else
  		dev_info(data->hwmon_dev, "Voltage normalised
  ");
  
  	sysfs_notify(&data->hwmon_dev->kobj, NULL, "in0_lcrit_alarm");
  }
  
  static void get_values_poll(struct work_struct *work)
  {
  	struct rpi_hwmon_data *data;
  
  	data = container_of(work, struct rpi_hwmon_data,
  			    get_values_poll_work.work);
  
  	rpi_firmware_get_throttled(data);
  
  	/*
  	 * We can't run faster than the sticky shift (100ms) since we get
  	 * flipping in the sticky bits that are cleared.
  	 */
  	schedule_delayed_work(&data->get_values_poll_work, 2 * HZ);
  }
  
  static int rpi_read(struct device *dev, enum hwmon_sensor_types type,
  		    u32 attr, int channel, long *val)
  {
  	struct rpi_hwmon_data *data = dev_get_drvdata(dev);
  
  	*val = !!(data->last_throttled & UNDERVOLTAGE_STICKY_BIT);
  	return 0;
  }
  
  static umode_t rpi_is_visible(const void *_data, enum hwmon_sensor_types type,
  			      u32 attr, int channel)
  {
  	return 0444;
  }

  static const struct hwmon_channel_info *rpi_info[] = {

  	HWMON_CHANNEL_INFO(in,
  			   HWMON_I_LCRIT_ALARM),

  	NULL
  };
  
  static const struct hwmon_ops rpi_hwmon_ops = {
  	.is_visible = rpi_is_visible,
  	.read = rpi_read,
  };
  
  static const struct hwmon_chip_info rpi_chip_info = {
  	.ops = &rpi_hwmon_ops,
  	.info = rpi_info,
  };
  
  static int rpi_hwmon_probe(struct platform_device *pdev)
  {
  	struct device *dev = &pdev->dev;
  	struct rpi_hwmon_data *data;

  
  	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
  	if (!data)
  		return -ENOMEM;
  
  	/* Parent driver assure that firmware is correct */
  	data->fw = dev_get_drvdata(dev->parent);

  	data->hwmon_dev = devm_hwmon_device_register_with_info(dev, "rpi_volt",
  							       data,
  							       &rpi_chip_info,
  							       NULL);
  
  	INIT_DELAYED_WORK(&data->get_values_poll_work, get_values_poll);
  	platform_set_drvdata(pdev, data);
  
  	if (!PTR_ERR_OR_ZERO(data->hwmon_dev))
  		schedule_delayed_work(&data->get_values_poll_work, 2 * HZ);
  
  	return PTR_ERR_OR_ZERO(data->hwmon_dev);
  }
  
  static int rpi_hwmon_remove(struct platform_device *pdev)
  {
  	struct rpi_hwmon_data *data = platform_get_drvdata(pdev);
  
  	cancel_delayed_work_sync(&data->get_values_poll_work);
  
  	return 0;
  }
  
  static struct platform_driver rpi_hwmon_driver = {
  	.probe = rpi_hwmon_probe,
  	.remove = rpi_hwmon_remove,
  	.driver = {
  		.name = "raspberrypi-hwmon",
  	},
  };
  module_platform_driver(rpi_hwmon_driver);

  MODULE_AUTHOR("Stefan Wahren <wahrenst@gmx.net>");

  MODULE_DESCRIPTION("Raspberry Pi voltage sensor driver");
  MODULE_LICENSE("GPL v2");

  MODULE_ALIAS("platform:raspberrypi-hwmon");