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/* 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;
}
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