libffs: Add ECC checking code

Add ECC checking code.  This code is based on the hostboot code.

Unused currently, but will be soon.  This uses __builtin_parityl() hence adding
libgcc linking previously.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

1 files changed, 175 insertions, 0 deletions

diff --git a/libflash/ecc.c b/libflash/ecc.c
new file mode 100644
index 0000000..9293743
--- /dev/null
+++ b/libflash/ecc.c
@@ -0,0 +1,175 @@
+/* Copyright 2013-2014 IBM Corp.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * 	http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ * implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* This is based on the hostboot ecc code */
+
+#include <stdint.h>
+#include <ecc.h>
+
+/*
+ * Matrix used for ECC calculation.
+ *
+ *  Each row of this is the set of data word bits that are used for
+ *  the calculation of the corresponding ECC bit.  The parity of the
+ *  bitset is the value of the ECC bit.
+ *
+ *  ie. ECC[n] = eccMatrix[n] & data
+ *
+ *  Note: To make the math easier (and less shifts in resulting code),
+ *        row0 = ECC7.  HW numbering is MSB, order here is LSB.
+ *
+ *  These values come from the HW design of the ECC algorithm.
+ */
+static uint64_t eccmatrix[] = {
+        0x0000e8423c0f99ff,
+        0x00e8423c0f99ff00,
+        0xe8423c0f99ff0000,
+        0x423c0f99ff0000e8,
+        0x3c0f99ff0000e842,
+        0x0f99ff0000e8423c,
+        0x99ff0000e8423c0f,
+        0xff0000e8423c0f99
+};
+
+/**
+ * Syndrome calculation matrix.
+ *
+ *  Maps syndrome to flipped bit.
+ *
+ *  To perform ECC correction, this matrix is a look-up of the bit
+ *  that is bad based on the binary difference of the good and bad
+ *  ECC.  This difference is called the "syndrome".
+ *
+ *  When a particular bit is on in the data, it cause a column from
+ *  eccMatrix being XOR'd into the ECC field.  This column is the
+ *  "effect" of each bit.  If a bit is flipped in the data then its
+ *  "effect" is missing from the ECC.  You can calculate ECC on unknown
+ *  quality data and compare the ECC field between the calculated
+ *  value and the stored value.  If the difference is zero, then the
+ *  data is clean.  If the difference is non-zero, you look up the
+ *  difference in the syndrome table to identify the "effect" that
+ *  is missing, which is the bit that is flipped.
+ *
+ *  Notice that ECC bit flips are recorded by a single "effect"
+ *  bit (ie. 0x1, 0x2, 0x4, 0x8 ...) and double bit flips are identified
+ *  by the UE status in the table.
+ *
+ *  Bits are in MSB order.
+ */
+static uint8_t syndromematrix[] = {
+        GD, E7, E6, UE, E5, UE, UE, 47, E4, UE, UE, 37, UE, 35, 39, UE,
+        E3, UE, UE, 48, UE, 30, 29, UE, UE, 57, 27, UE, 31, UE, UE, UE,
+        E2, UE, UE, 17, UE, 18, 40, UE, UE, 58, 22, UE, 21, UE, UE, UE,
+        UE, 16, 49, UE, 19, UE, UE, UE, 23, UE, UE, UE, UE, 20, UE, UE,
+        E1, UE, UE, 51, UE, 46,  9, UE, UE, 34, 10, UE, 32, UE, UE, 36,
+        UE, 62, 50, UE, 14, UE, UE, UE, 13, UE, UE, UE, UE, UE, UE, UE,
+        UE, 61,  8, UE, 41, UE, UE, UE, 11, UE, UE, UE, UE, UE, UE, UE,
+        15, UE, UE, UE, UE, UE, UE, UE, UE, UE, 12, UE, UE, UE, UE, UE,
+        E0, UE, UE, 55, UE, 45, 43, UE, UE, 56, 38, UE,  1, UE, UE, UE,
+        UE, 25, 26, UE,  2, UE, UE, UE, 24, UE, UE, UE, UE, UE, 28, UE,
+        UE, 59, 54, UE, 42, UE, UE, 44,  6, UE, UE, UE, UE, UE, UE, UE,
+         5, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE,
+        UE, 63, 53, UE,  0, UE, UE, UE, 33, UE, UE, UE, UE, UE, UE, UE,
+         3, UE, UE, 52, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE,
+         7, UE, UE, UE, UE, UE, UE, UE, UE, 60, UE, UE, UE, UE, UE, UE,
+        UE, UE, UE, UE,  4, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE, UE,
+};
+
+/**
+ * Create the ECC field corresponding to a 8-byte data field
+ *
+ *  @data:	The 8 byte data to generate ECC for.
+ *  @return:	The 1 byte ECC corresponding to the data.
+ */
+static uint8_t eccgenerate(uint64_t data)
+{
+	int i;
+        uint8_t result = 0;
+
+        for (i = 0; i < 8; i++)
+		result |= __builtin_parityl(eccmatrix[i] & data) << i;
+
+        return result;
+}
+
+/**
+ * Verify the data and ECC match or indicate how they are wrong.
+ *
+ * @data:	The data to check ECC on.
+ * @ecc:	The [supposed] ECC for the data.
+ *
+ * @return:	eccBitfield or 0-64.
+ *
+ * @retval GD - Indicates the data is good (matches ECC).
+ * @retval UE - Indicates the data is uncorrectable.
+ * @retval all others - Indication of which bit is incorrect.
+ */
+static uint8_t eccverify(uint64_t data, uint8_t ecc)
+{
+        return syndromematrix[eccgenerate(data) ^ ecc];
+}
+
+/**
+ * Copy data from an input buffer with ECC to an output buffer without ECC.
+ * Correct it along the way and check for errors.
+ *
+ * @dst:	destination buffer without ECC
+ * @src:	source buffer with ECC
+ * @len:	number of bytes of data to copy (without ecc).
+                     Must be 8 byte aligned.
+ *
+ * @return:	eccBitfield or 0-64.
+ *
+ * @retval GD - Data is good.
+ * @retval UE - Data is uncorrectable.
+ * @retval all others - which bit was corrected.
+ */
+uint8_t eccmemcpy(uint64_t *dst, uint64_t *src, uint32_t len)
+{
+	uint64_t *data;
+	uint8_t *ecc;
+	uint32_t i;
+	uint8_t badbit;
+
+	if (len & 0x7) {
+		/* TODO: we could probably handle this */
+		prerror("ECC data length must be 8 byte aligned length:%i\n",
+			len);
+		return UE;
+	}
+
+	/* Handle in chunks of 8 bytes, so adjust the length */
+	len >>= 3;
+
+	for (i = 0; i < len; i++) {
+		data = (uint64_t *)((uint8_t *)src + i*9);
+		ecc = (uint8_t *)data + 8;
+
+		badbit = eccverify(*data, *ecc);
+		if (badbit == UE) {
+			prerror("ECC: uncorrectable error: %016lx %02x\n",
+				(long unsigned int)*data, *ecc);
+			return badbit;
+		}
+		*dst = *data;
+		if (badbit <= UE)
+			prlog(PR_INFO, "ECC: correctable error: %i\n", badbit);
+		if (badbit < 64)
+			*dst = *data ^ (1ul << (63 - badbit));
+		dst++;
+        }
+        return GD;
+}