/* ir-rc6-decoder.c - A decoder for the RC6 IR protocol
   *
   * Copyright (C) 2010 by David Härdeman <david@hardeman.nu>
   *
   * 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 version 2 of the License.
   *
   * 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 "rc-core-priv.h"
  #include <linux/module.h>
  
  /*
   * This decoder currently supports:
   * RC6-0-16	(standard toggle bit in header)
   * RC6-6A-20	(no toggle bit)
   * RC6-6A-24	(no toggle bit)
   * RC6-6A-32	(MCE version with toggle bit in body)
   */
  
  #define RC6_UNIT		444444	/* nanosecs */
  #define RC6_HEADER_NBITS	4	/* not including toggle bit */
  #define RC6_0_NBITS		16
  #define RC6_6A_32_NBITS		32
  #define RC6_6A_NBITS		128	/* Variable 8..128 */
  #define RC6_PREFIX_PULSE	(6 * RC6_UNIT)
  #define RC6_PREFIX_SPACE	(2 * RC6_UNIT)
  #define RC6_BIT_START		(1 * RC6_UNIT)
  #define RC6_BIT_END		(1 * RC6_UNIT)
  #define RC6_TOGGLE_START	(2 * RC6_UNIT)
  #define RC6_TOGGLE_END		(2 * RC6_UNIT)
  #define RC6_SUFFIX_SPACE	(6 * RC6_UNIT)
  #define RC6_MODE_MASK		0x07	/* for the header bits */
  #define RC6_STARTBIT_MASK	0x08	/* for the header bits */
  #define RC6_6A_MCE_TOGGLE_MASK	0x8000	/* for the body bits */
  #define RC6_6A_LCC_MASK		0xffff0000 /* RC6-6A-32 long customer code mask */
  #define RC6_6A_MCE_CC		0x800f0000 /* MCE customer code */
  #ifndef CHAR_BIT
  #define CHAR_BIT 8	/* Normally in <limits.h> */
  #endif
  
  enum rc6_mode {
  	RC6_MODE_0,
  	RC6_MODE_6A,
  	RC6_MODE_UNKNOWN,
  };
  
  enum rc6_state {
  	STATE_INACTIVE,
  	STATE_PREFIX_SPACE,
  	STATE_HEADER_BIT_START,
  	STATE_HEADER_BIT_END,
  	STATE_TOGGLE_START,
  	STATE_TOGGLE_END,
  	STATE_BODY_BIT_START,
  	STATE_BODY_BIT_END,
  	STATE_FINISHED,
  };
  
  static enum rc6_mode rc6_mode(struct rc6_dec *data)
  {
  	switch (data->header & RC6_MODE_MASK) {
  	case 0:
  		return RC6_MODE_0;
  	case 6:
  		if (!data->toggle)
  			return RC6_MODE_6A;
  		/* fall through */
  	default:
  		return RC6_MODE_UNKNOWN;
  	}
  }
  
  /**
   * ir_rc6_decode() - Decode one RC6 pulse or space
   * @dev:	the struct rc_dev descriptor of the device
   * @ev:		the struct ir_raw_event descriptor of the pulse/space
   *
   * This function returns -EINVAL if the pulse violates the state machine
   */
  static int ir_rc6_decode(struct rc_dev *dev, struct ir_raw_event ev)
  {
  	struct rc6_dec *data = &dev->raw->rc6;
  	u32 scancode;
  	u8 toggle;
  
  	if (!(dev->enabled_protocols &
  	      (RC_BIT_RC6_0 | RC_BIT_RC6_6A_20 | RC_BIT_RC6_6A_24 |
  	       RC_BIT_RC6_6A_32 | RC_BIT_RC6_MCE)))
  		return 0;
  
  	if (!is_timing_event(ev)) {
  		if (ev.reset)
  			data->state = STATE_INACTIVE;
  		return 0;
  	}
  
  	if (!geq_margin(ev.duration, RC6_UNIT, RC6_UNIT / 2))
  		goto out;
  
  again:
  	IR_dprintk(2, "RC6 decode started at state %i (%uus %s)
  ",
  		   data->state, TO_US(ev.duration), TO_STR(ev.pulse));
  
  	if (!geq_margin(ev.duration, RC6_UNIT, RC6_UNIT / 2))
  		return 0;
  
  	switch (data->state) {
  
  	case STATE_INACTIVE:
  		if (!ev.pulse)
  			break;
  
  		/* Note: larger margin on first pulse since each RC6_UNIT
  		   is quite short and some hardware takes some time to
  		   adjust to the signal */
  		if (!eq_margin(ev.duration, RC6_PREFIX_PULSE, RC6_UNIT))
  			break;
  
  		data->state = STATE_PREFIX_SPACE;
  		data->count = 0;
  		return 0;
  
  	case STATE_PREFIX_SPACE:
  		if (ev.pulse)
  			break;
  
  		if (!eq_margin(ev.duration, RC6_PREFIX_SPACE, RC6_UNIT / 2))
  			break;
  
  		data->state = STATE_HEADER_BIT_START;
  		data->header = 0;
  		return 0;
  
  	case STATE_HEADER_BIT_START:
  		if (!eq_margin(ev.duration, RC6_BIT_START, RC6_UNIT / 2))
  			break;
  
  		data->header <<= 1;
  		if (ev.pulse)
  			data->header |= 1;
  		data->count++;
  		data->state = STATE_HEADER_BIT_END;
  		return 0;
  
  	case STATE_HEADER_BIT_END:
  		if (!is_transition(&ev, &dev->raw->prev_ev))
  			break;
  
  		if (data->count == RC6_HEADER_NBITS)
  			data->state = STATE_TOGGLE_START;
  		else
  			data->state = STATE_HEADER_BIT_START;
  
  		decrease_duration(&ev, RC6_BIT_END);
  		goto again;
  
  	case STATE_TOGGLE_START:
  		if (!eq_margin(ev.duration, RC6_TOGGLE_START, RC6_UNIT / 2))
  			break;
  
  		data->toggle = ev.pulse;
  		data->state = STATE_TOGGLE_END;
  		return 0;
  
  	case STATE_TOGGLE_END:
  		if (!is_transition(&ev, &dev->raw->prev_ev) ||
  		    !geq_margin(ev.duration, RC6_TOGGLE_END, RC6_UNIT / 2))
  			break;
  
  		if (!(data->header & RC6_STARTBIT_MASK)) {
  			IR_dprintk(1, "RC6 invalid start bit
  ");
  			break;
  		}
  
  		data->state = STATE_BODY_BIT_START;
  		decrease_duration(&ev, RC6_TOGGLE_END);
  		data->count = 0;
  		data->body = 0;
  
  		switch (rc6_mode(data)) {
  		case RC6_MODE_0:
  			data->wanted_bits = RC6_0_NBITS;
  			break;
  		case RC6_MODE_6A:
  			data->wanted_bits = RC6_6A_NBITS;
  			break;
  		default:
  			IR_dprintk(1, "RC6 unknown mode
  ");
  			goto out;
  		}
  		goto again;
  
  	case STATE_BODY_BIT_START:
  		if (eq_margin(ev.duration, RC6_BIT_START, RC6_UNIT / 2)) {
  			/* Discard LSB's that won't fit in data->body */
  			if (data->count++ < CHAR_BIT * sizeof data->body) {
  				data->body <<= 1;
  				if (ev.pulse)
  					data->body |= 1;
  			}
  			data->state = STATE_BODY_BIT_END;
  			return 0;
  		} else if (RC6_MODE_6A == rc6_mode(data) && !ev.pulse &&
  				geq_margin(ev.duration, RC6_SUFFIX_SPACE, RC6_UNIT / 2)) {
  			data->state = STATE_FINISHED;
  			goto again;
  		}
  		break;
  
  	case STATE_BODY_BIT_END:
  		if (!is_transition(&ev, &dev->raw->prev_ev))
  			break;
  
  		if (data->count == data->wanted_bits)
  			data->state = STATE_FINISHED;
  		else
  			data->state = STATE_BODY_BIT_START;
  
  		decrease_duration(&ev, RC6_BIT_END);
  		goto again;
  
  	case STATE_FINISHED:
  		if (ev.pulse)
  			break;
  
  		switch (rc6_mode(data)) {
  		case RC6_MODE_0:
  			scancode = data->body;
  			toggle = data->toggle;
  			IR_dprintk(1, "RC6(0) scancode 0x%04x (toggle: %u)
  ",
  				   scancode, toggle);
  			break;
  		case RC6_MODE_6A:
  			if (data->count > CHAR_BIT * sizeof data->body) {
  				IR_dprintk(1, "RC6 too many (%u) data bits
  ",
  					data->count);
  				goto out;
  			}
  
  			scancode = data->body;
  			if (data->count == RC6_6A_32_NBITS &&
  					(scancode & RC6_6A_LCC_MASK) == RC6_6A_MCE_CC) {
  				/* MCE RC */
  				toggle = (scancode & RC6_6A_MCE_TOGGLE_MASK) ? 1 : 0;
  				scancode &= ~RC6_6A_MCE_TOGGLE_MASK;
  			} else {
  				toggle = 0;
  			}
  			IR_dprintk(1, "RC6(6A) scancode 0x%08x (toggle: %u)
  ",
  				   scancode, toggle);
  			break;
  		default:
  			IR_dprintk(1, "RC6 unknown mode
  ");
  			goto out;
  		}
  
  		rc_keydown(dev, scancode, toggle);
  		data->state = STATE_INACTIVE;
  		return 0;
  	}
  
  out:
  	IR_dprintk(1, "RC6 decode failed at state %i (%uus %s)
  ",
  		   data->state, TO_US(ev.duration), TO_STR(ev.pulse));
  	data->state = STATE_INACTIVE;
  	return -EINVAL;
  }
  
  static struct ir_raw_handler rc6_handler = {
  	.protocols	= RC_BIT_RC6_0 | RC_BIT_RC6_6A_20 |
  			  RC_BIT_RC6_6A_24 | RC_BIT_RC6_6A_32 |
  			  RC_BIT_RC6_MCE,
  	.decode		= ir_rc6_decode,
  };
  
  static int __init ir_rc6_decode_init(void)
  {
  	ir_raw_handler_register(&rc6_handler);
  
  	printk(KERN_INFO "IR RC6 protocol handler initialized
  ");
  	return 0;
  }
  
  static void __exit ir_rc6_decode_exit(void)
  {
  	ir_raw_handler_unregister(&rc6_handler);
  }
  
  module_init(ir_rc6_decode_init);
  module_exit(ir_rc6_decode_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("David Härdeman <david@hardeman.nu>");
  MODULE_DESCRIPTION("RC6 IR protocol decoder");