mtd: mtd_nandecctest: add single bit error correction test

This adds the single bit error correction test case listed below:

Prepare data block without corruption and ECC data with single bit error,
and verify that the data block is preserved by __nand_correct_data().
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/tests/mtd_nandecctest.c

@@ -48,6 +48,31 @@ static void single_bit_error_data(void *error_data, void *correct_data,
 	__change_bit_le(offset, error_data);
 }
 
+static unsigned int random_ecc_bit(size_t size)
+{
+	unsigned int offset = random32() % (3 * BITS_PER_BYTE);
+
+	if (size == 256) {
+		/*
+		 * Don't inject a bit error into the insignificant bits (16th
+		 * and 17th bit) in ECC code for 256 byte data block
+		 */
+		while (offset == 16 || offset == 17)
+			offset = random32() % (3 * BITS_PER_BYTE);
+	}
+
+	return offset;
+}
+
+static void single_bit_error_ecc(void *error_ecc, void *correct_ecc,
+				size_t size)
+{
+	unsigned int offset = random_ecc_bit(size);
+
+	memcpy(error_ecc, correct_ecc, 3);
+	__change_bit_le(offset, error_ecc);
+}
+
 static void no_bit_error(void *error_data, void *error_ecc,
 		void *correct_data, void *correct_ecc, const size_t size)
 {
@@ -76,6 +101,13 @@ static void single_bit_error_in_data(void *error_data, void *error_ecc,
 	memcpy(error_ecc, correct_ecc, 3);
 }
 
+static void single_bit_error_in_ecc(void *error_data, void *error_ecc,
+		void *correct_data, void *correct_ecc, const size_t size)
+{
+	memcpy(error_data, correct_data, size);
+	single_bit_error_ecc(error_ecc, correct_ecc, size);
+}
+
 static int single_bit_error_correct(void *error_data, void *error_ecc,
 				void *correct_data, const size_t size)
 {
@@ -101,6 +133,11 @@ static const struct nand_ecc_test nand_ecc_test[] = {
 		.prepare = single_bit_error_in_data,
 		.verify = single_bit_error_correct,
 	},
+	{
+		.name = "single-bit-error-in-ecc-correct",
+		.prepare = single_bit_error_in_ecc,
+		.verify = single_bit_error_correct,
+	},
 };
 
 static void dump_data_ecc(void *error_data, void *error_ecc, void *correct_data,