/*
   * i2c-smbus.c - SMBus extensions to the I2C protocol
   *
   * Copyright (C) 2008 David Brownell
   * Copyright (C) 2010 Jean Delvare <jdelvare@suse.de>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/device.h>
  #include <linux/interrupt.h>
  #include <linux/workqueue.h>
  #include <linux/i2c.h>
  #include <linux/i2c-smbus.h>
  #include <linux/slab.h>
  
  struct i2c_smbus_alert {
  	unsigned int		alert_edge_triggered:1;
  	int			irq;
  	struct work_struct	alert;
  	struct i2c_client	*ara;		/* Alert response address */
  };
  
  struct alert_data {
  	unsigned short		addr;
  	u8			flag:1;
  };
  
  /* If this is the alerting device, notify its driver */
  static int smbus_do_alert(struct device *dev, void *addrp)
  {
  	struct i2c_client *client = i2c_verify_client(dev);
  	struct alert_data *data = addrp;
  	struct i2c_driver *driver;
  
  	if (!client || client->addr != data->addr)
  		return 0;
  	if (client->flags & I2C_CLIENT_TEN)
  		return 0;
  
  	/*
  	 * Drivers should either disable alerts, or provide at least
  	 * a minimal handler.  Lock so the driver won't change.
  	 */
  	device_lock(dev);
  	if (client->dev.driver) {
  		driver = to_i2c_driver(client->dev.driver);
  		if (driver->alert)
  			driver->alert(client, data->flag);
  		else
  			dev_warn(&client->dev, "no driver alert()!
  ");
  	} else
  		dev_dbg(&client->dev, "alert with no driver
  ");
  	device_unlock(dev);
  
  	/* Stop iterating after we find the device */
  	return -EBUSY;
  }
  
  /*
   * The alert IRQ handler needs to hand work off to a task which can issue
   * SMBus calls, because those sleeping calls can't be made in IRQ context.
   */
  static void smbus_alert(struct work_struct *work)
  {
  	struct i2c_smbus_alert *alert;
  	struct i2c_client *ara;
  	unsigned short prev_addr = 0;	/* Not a valid address */
  
  	alert = container_of(work, struct i2c_smbus_alert, alert);
  	ara = alert->ara;
  
  	for (;;) {
  		s32 status;
  		struct alert_data data;
  
  		/*
  		 * Devices with pending alerts reply in address order, low
  		 * to high, because of slave transmit arbitration.  After
  		 * responding, an SMBus device stops asserting SMBALERT#.
  		 *
  		 * Note that SMBus 2.0 reserves 10-bit addresses for future
  		 * use.  We neither handle them, nor try to use PEC here.
  		 */
  		status = i2c_smbus_read_byte(ara);
  		if (status < 0)
  			break;
  
  		data.flag = status & 1;
  		data.addr = status >> 1;
  
  		if (data.addr == prev_addr) {
  			dev_warn(&ara->dev, "Duplicate SMBALERT# from dev "
  				"0x%02x, skipping
  ", data.addr);
  			break;
  		}
  		dev_dbg(&ara->dev, "SMBALERT# from dev 0x%02x, flag %d
  ",
  			data.addr, data.flag);
  
  		/* Notify driver for the device which issued the alert */
  		device_for_each_child(&ara->adapter->dev, &data,
  				      smbus_do_alert);
  		prev_addr = data.addr;
  	}
  
  	/* We handled all alerts; re-enable level-triggered IRQs */
  	if (!alert->alert_edge_triggered)
  		enable_irq(alert->irq);
  }
  
  static irqreturn_t smbalert_irq(int irq, void *d)
  {
  	struct i2c_smbus_alert *alert = d;
  
  	/* Disable level-triggered IRQs until we handle them */
  	if (!alert->alert_edge_triggered)
  		disable_irq_nosync(irq);
  
  	schedule_work(&alert->alert);
  	return IRQ_HANDLED;
  }
  
  /* Setup SMBALERT# infrastructure */
  static int smbalert_probe(struct i2c_client *ara,
  			  const struct i2c_device_id *id)
  {
  	struct i2c_smbus_alert_setup *setup = dev_get_platdata(&ara->dev);
  	struct i2c_smbus_alert *alert;
  	struct i2c_adapter *adapter = ara->adapter;
  	int res;
  
  	alert = devm_kzalloc(&ara->dev, sizeof(struct i2c_smbus_alert),
  			     GFP_KERNEL);
  	if (!alert)
  		return -ENOMEM;
  
  	alert->alert_edge_triggered = setup->alert_edge_triggered;
  	alert->irq = setup->irq;
  	INIT_WORK(&alert->alert, smbus_alert);
  	alert->ara = ara;
  
  	if (setup->irq > 0) {
  		res = devm_request_irq(&ara->dev, setup->irq, smbalert_irq,
  				       0, "smbus_alert", alert);
  		if (res)
  			return res;
  	}
  
  	i2c_set_clientdata(ara, alert);
  	dev_info(&adapter->dev, "supports SMBALERT#, %s trigger
  ",
  		 setup->alert_edge_triggered ? "edge" : "level");
  
  	return 0;
  }
  
  /* IRQ and memory resources are managed so they are freed automatically */
  static int smbalert_remove(struct i2c_client *ara)
  {
  	struct i2c_smbus_alert *alert = i2c_get_clientdata(ara);
  
  	cancel_work_sync(&alert->alert);
  	return 0;
  }
  
  static const struct i2c_device_id smbalert_ids[] = {
  	{ "smbus_alert", 0 },
  	{ /* LIST END */ }
  };
  MODULE_DEVICE_TABLE(i2c, smbalert_ids);
  
  static struct i2c_driver smbalert_driver = {
  	.driver = {
  		.name	= "smbus_alert",
  	},
  	.probe		= smbalert_probe,
  	.remove		= smbalert_remove,
  	.id_table	= smbalert_ids,
  };
  
  /**
   * i2c_setup_smbus_alert - Setup SMBus alert support
   * @adapter: the target adapter
   * @setup: setup data for the SMBus alert handler
   * Context: can sleep
   *
   * Setup handling of the SMBus alert protocol on a given I2C bus segment.
   *
   * Handling can be done either through our IRQ handler, or by the
   * adapter (from its handler, periodic polling, or whatever).
   *
   * NOTE that if we manage the IRQ, we *MUST* know if it's level or
   * edge triggered in order to hand it to the workqueue correctly.
   * If triggering the alert seems to wedge the system, you probably
   * should have said it's level triggered.
   *
   * This returns the ara client, which should be saved for later use with
   * i2c_handle_smbus_alert() and ultimately i2c_unregister_device(); or NULL
   * to indicate an error.
   */
  struct i2c_client *i2c_setup_smbus_alert(struct i2c_adapter *adapter,
  					 struct i2c_smbus_alert_setup *setup)
  {
  	struct i2c_board_info ara_board_info = {
  		I2C_BOARD_INFO("smbus_alert", 0x0c),
  		.platform_data = setup,
  	};
  
  	return i2c_new_device(adapter, &ara_board_info);
  }
  EXPORT_SYMBOL_GPL(i2c_setup_smbus_alert);
  
  /**
   * i2c_handle_smbus_alert - Handle an SMBus alert
   * @ara: the ARA client on the relevant adapter
   * Context: can't sleep
   *
   * Helper function to be called from an I2C bus driver's interrupt
   * handler. It will schedule the alert work, in turn calling the
   * corresponding I2C device driver's alert function.
   *
   * It is assumed that ara is a valid i2c client previously returned by
   * i2c_setup_smbus_alert().
   */
  int i2c_handle_smbus_alert(struct i2c_client *ara)
  {
  	struct i2c_smbus_alert *alert = i2c_get_clientdata(ara);
  
  	return schedule_work(&alert->alert);
  }
  EXPORT_SYMBOL_GPL(i2c_handle_smbus_alert);
  
  module_i2c_driver(smbalert_driver);
  
  MODULE_AUTHOR("Jean Delvare <jdelvare@suse.de>");
  MODULE_DESCRIPTION("SMBus protocol extensions support");
  MODULE_LICENSE("GPL");