From 15b5423757a750b2c7efabd77bb6ed8aa6ffb20e Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 21 Oct 2004 00:55:08 +0100
Subject: Shared Reed-Solomon ECC library

The attached patch contains a shared Reed-Solomon Library analogous to
the shared zlib.

(N)AND FLASH is gaining popularity and there are a lot of ASIC/SoC/FPGA
controllers around which implement hardware support for Reed-Solomon
error correction. As usual they use different implementations
(polynomials etc.). So it's obvious to use a shared library for the
common tasks of error correction.

A short scan through the kernel revealed that at least the ftape driver
uses Reed-Solomon error correction. It could be easily converted to use
the shared library code.

The encoder/decoder code is lifted from the GPL'd userspace RS-library
written by Phil Karn. I modified/wrapped it to provide the different
functions which we need in the MTD/NAND code.

The library is tested in extenso under various MTD/NAND configurations.

The lib should be usable for other purposes right out of the box.
Adjustment for currently not implemented functionality is an easy task.

I'm willing to take the maintainership of the library.

Signed-Off-By: Thomas Gleixner <tglx@linutronix.de>
Signed-Off-By: David Woodhouse <dwmw2@infradead.org>
"No objections at all. Just keep the authorship notices." -- Phil Karn
---
 include/linux/rslib.h | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 include/linux/rslib.h

(limited to 'include')

diff --git a/include/linux/rslib.h b/include/linux/rslib.h
new file mode 100644
index 000000000000..980c8f74d8dc
--- /dev/null
+++ b/include/linux/rslib.h
@@ -0,0 +1,105 @@
+/* 
+ * include/linux/rslib.h
+ *
+ * Overview:
+ *   Generic Reed Solomon encoder / decoder library
+ *   
+ * Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
+ *
+ * RS code lifted from reed solomon library written by Phil Karn
+ * Copyright 2002 Phil Karn, KA9Q
+ *
+ * $Id: rslib.h,v 1.3 2004/10/05 22:08:22 gleixner Exp $
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _RSLIB_H_
+#define _RSLIB_H_
+
+#include <linux/list.h>
+
+/** 
+ * struct rs_control - rs control structure
+ * 
+ * @mm:		Bits per symbol
+ * @nn:		Symbols per block (= (1<<mm)-1)
+ * @alpha_to:	log lookup table
+ * @index_of:	Antilog lookup table
+ * @genpoly:	Generator polynomial 
+ * @nroots:	Number of generator roots = number of parity symbols
+ * @fcr:	First consecutive root, index form
+ * @prim:	Primitive element, index form 
+ * @iprim:	prim-th root of 1, index form 
+ * @gfpoly:	The primitive generator polynominal 
+ * @users:	Users of this structure 
+ * @list:	List entry for the rs control list
+*/
+struct rs_control {
+	int 		mm;
+	int 		nn;
+	uint16_t	*alpha_to;
+	uint16_t	*index_of;
+	uint16_t	*genpoly;
+	int 		nroots;
+	int 		fcr;
+	int 		prim;
+	int 		iprim;
+	int		gfpoly;
+	int		users;
+	struct list_head list;
+};
+
+/* General purpose RS codec, 8-bit data width, symbol width 1-15 bit  */
+#ifdef CONFIG_REED_SOLOMON_ENC8
+int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
+	       uint16_t invmsk);
+#endif
+#ifdef CONFIG_REED_SOLOMON_DEC8
+int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len, 
+		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
+	       uint16_t *corr);
+#endif
+
+/* General purpose RS codec, 16-bit data width, symbol width 1-15 bit  */
+#ifdef CONFIG_REED_SOLOMON_ENC16
+int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
+		uint16_t invmsk);
+#endif
+#ifdef CONFIG_REED_SOLOMON_DEC16
+int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
+		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
+		uint16_t *corr);
+#endif
+
+/* Create or get a matching rs control structure */
+struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim, 
+			   int nroots);
+
+/* Release a rs control structure */
+void free_rs(struct rs_control *rs);
+
+/** modulo replacement for galois field arithmetics
+ *
+ *  @rs:	the rs control structure
+ *  @x:		the value to reduce
+ *
+ *  where
+ *  rs->mm = number of bits per symbol	
+ *  rs->nn = (2^rs->mm) - 1
+ *  
+ *  Simple arithmetic modulo would return a wrong result for values
+ *  >= 3 * rs->nn
+*/
+static inline int rs_modnn(struct rs_control *rs, int x)
+{
+	while (x >= rs->nn) {
+		x -= rs->nn;
+		x = (x >> rs->mm) + (x & rs->nn);
+	}
+	return x;
+}
+
+#endif
-- 
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