[RFC] ir-rc6-decoder: Support RC6-6A variable length data

[Lawrence Rust <lawrence@softsystem.co.uk>]

Hi,

This patch to the IR RC6 decoder adds support for variable length
mode-6A frames which can range in size from 8 to 128 bits.  Please refer
to the following link for a detailed explanation or RC6 frames:
http://slydiman.narod.ru/scr/kb/rc6.htm

This change removes the assumption that frames are fixed length
(currently either 24 or 32 data bits) and actually counts the number of
bits until an end of frame marker is seen.

This change adds support for Sky/Sky+ RC's that transmit RC6-6A-24 i.e.
24 bit data.

The patch was made against git tag v2.6.39 and was tested with a MCE-USB
and a Sky RC.

Comments & suggestions please.
--
Lawrence Rust

>From 44431fd36f4b766d2b26ff70fb79b9a7c9e869fe Mon Sep 17 00:00:00 2001
From: Lawrence Rust <lvr@softsystem.co.uk>
Date: Mon, 26 Sep 2011 15:21:13 +0200
Subject: [PATCH] ir-rc6-decoder: Support RC6-6A variable length body

Signed-off-by: Lawrence Rust <lvr@softsystem.co.uk>
---
 drivers/media/rc/ir-rc6-decoder.c |   65 ++++++++++++++++++++++---------------
 1 files changed, 39 insertions(+), 26 deletions(-)

diff --git a/drivers/media/rc/ir-rc6-decoder.c b/drivers/media/rc/ir-rc6-decoder.c
index 755dafa..015038a 100644
--- a/drivers/media/rc/ir-rc6-decoder.c
+++ b/drivers/media/rc/ir-rc6-decoder.c
@@ -17,24 +17,31 @@
 /*
  * 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	/* us */
+#define RC6_UNIT		444444	/* nanosecs */
 #define RC6_HEADER_NBITS	4	/* not including toggle bit */
 #define RC6_0_NBITS		16
-#define RC6_6A_SMALL_NBITS	24
-#define RC6_6A_LARGE_NBITS	32
+#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,
@@ -124,6 +131,7 @@ again:
 			break;
 
 		data->state = STATE_HEADER_BIT_START;
+		data->header = 0;
 		return 0;
 
 	case STATE_HEADER_BIT_START:
@@ -170,20 +178,14 @@ again:
 		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:
-			/* This might look weird, but we basically
-			   check the value of the first body bit to
-			   determine the number of bits in mode 6A */
-			if ((!ev.pulse && !geq_margin(ev.duration, RC6_UNIT, RC6_UNIT / 2)) ||
-			    geq_margin(ev.duration, RC6_UNIT, RC6_UNIT / 2))
-				data->wanted_bits = RC6_6A_LARGE_NBITS;
-			else
-				data->wanted_bits = RC6_6A_SMALL_NBITS;
+			data->wanted_bits = RC6_6A_NBITS;
 			break;
 		default:
 			IR_dprintk(1, "RC6 unknown mode\n");
@@ -192,15 +194,21 @@ again:
 		goto again;
 
 	case STATE_BODY_BIT_START:
-		if (!eq_margin(ev.duration, RC6_BIT_START, RC6_UNIT / 2))
-			break;
-
-		data->body <<= 1;
-		if (ev.pulse)
-			data->body |= 1;
-		data->count++;
-		data->state = STATE_BODY_BIT_END;
-		return 0;
+		if (eq_margin(ev.duration, RC6_BIT_START, RC6_UNIT / 2)) {
+			/* Discard data bits 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))
@@ -220,20 +228,21 @@ again:
 
 		switch (rc6_mode(data)) {
 		case RC6_MODE_0:
-			scancode = data->body & 0xffff;
+			scancode = data->body;
 			toggle = data->toggle;
 			IR_dprintk(1, "RC6(0) scancode 0x%04x (toggle: %u)\n",
 				   scancode, toggle);
 			break;
 		case RC6_MODE_6A:
-			if (data->wanted_bits == RC6_6A_LARGE_NBITS) {
-				toggle = data->body & RC6_6A_MCE_TOGGLE_MASK ? 1 : 0;
-				scancode = data->body & ~RC6_6A_MCE_TOGGLE_MASK;
+			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;
-				scancode = data->body & 0xffffff;
 			}
-
 			IR_dprintk(1, "RC6(6A) scancode 0x%08x (toggle: %u)\n",
 				   scancode, toggle);
 			break;
@@ -242,6 +251,10 @@ again:
 			goto out;
 		}
 
+		if (data->count > CHAR_BIT * sizeof data->body)
+			IR_dprintk(1, "RC6 scancode truncated from %u bits\n",
+				data->count);
+
 		rc_keydown(dev, scancode, toggle);
 		data->state = STATE_INACTIVE;
 		return 0;
-- 
1.7.4.1