device/dram/ddr2.c: Add methods to compute to identify dram

DDR2 DIMMs are uniquely defined by SPD byte 64 till 72 and 93 till
98. Compute a crc16 over that data to provide a solid way to check
DIMM identify.

Reuse the crc16 function from ddr3.c to do this.

Change-Id: I3c0c42786197f9b4eb3e42261c10ff5e4266120f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/23345
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/device/dram/ddr2.c

@@ -71,6 +71,30 @@ u8 spd_ddr2_calc_checksum(u8 *spd, int len)
 	return c;
 }
 
+/**
+ * \brief Calculate the CRC of a DDR2 SPD unique identifier
+ *
+ * @param spd pointer to raw SPD data
+ * @param len length of data in SPD
+ *
+ * @return the CRC of SPD data bytes 64..72 and 93..98, or 0
+ *  when spd data is truncated.
+ */
+u16 spd_ddr2_calc_unique_crc(const u8 *spd, int len)
+{
+	u8 id_bytes[15];
+	int i, j = 0;
+	if (len < 98)
+		/* Not enough bytes available to get the CRC */
+		return 0;
+	for (i = 64; i <= 72; i++)
+		id_bytes[j++] = spd[i];
+	for (i = 93; i <= 98; i++)
+		id_bytes[j++] = spd[i];
+
+	return ddr3_crc16(id_bytes, 15);
+}
+
 /**
  * \brief Return size of SPD.
  *

src/device/dram/ddr3.c

@@ -46,7 +46,7 @@ int spd_dimm_is_registered_ddr3(enum spd_dimm_type type)
 	return 0;
 }
 
-static u16 crc16(const u8 *ptr, int n_crc)
+u16 ddr3_crc16(const u8 *ptr, int n_crc)
 {
 	int i;
 	u16 crc = 0;
@@ -87,7 +87,7 @@ u16 spd_ddr3_calc_crc(u8 *spd, int len)
 		/* Not enough bytes available to get the CRC */
 		return 0;
 
-	return crc16(spd, n_crc);
+	return ddr3_crc16(spd, n_crc);
 }
 
 /**
@@ -104,7 +104,7 @@ u16 spd_ddr3_calc_unique_crc(u8 *spd, int len)
 		/* Not enough bytes available to get the CRC */
 		return 0;
 
-	return crc16(&spd[117], 11);
+	return ddr3_crc16(&spd[117], 11);
 }
 
 /**

src/include/device/dram/common.h

@@ -67,4 +67,6 @@ enum spd_status {
 	SPD_STATUS_INVALID_FIELD,
 };
 
+u16 ddr3_crc16(const u8 *ptr, int n_crc);
+
 #endif /* DEVICE_DRAM_COMMON_H */

src/include/device/dram/ddr2.h

@@ -179,5 +179,6 @@ int spd_decode_ddr2(struct dimm_attr_ddr2_st *dimm, u8 spd[SPD_SIZE_MAX_DDR2]);
 void dram_print_spd_ddr2(const struct dimm_attr_ddr2_st *dimm);
 void normalize_tck(u32 *tclk);
 u8 spd_get_msbs(u8 c);
+u16 spd_ddr2_calc_unique_crc(const u8 *spd, int len);
 
 #endif /* DEVICE_DRAM_DDR2L_H */