board: sifive: Add an interface to get PCB revision

There are different DDR parameter settings for different board
revisions. Add a new interface to get the PCB revision to determine
which DT should be selected at runtime.

Signed-off-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

arch/riscv/include/asm/arch-fu740/eeprom.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2021 SiFive, Inc.
+ *
+ * Zong Li <zong.li@sifve.com>
+ */
+
+#ifndef _ASM_RISCV_EEPROM_H
+#define _ASM_RISCV_EEPROM_H
+
+#define PCB_REVISION_REV3	0x3
+
+u8 get_pcb_revision_from_eeprom(void);
+
+#endif /* _ASM_RISCV_EEPROM_H */

board/sifive/unmatched/hifive-platform-i2c-eeprom.c

@@ -540,3 +540,35 @@ int mac_read_from_eeprom(void)
 
 	return 0;
 }
+
+/**
+ * get_pcb_revision_from_eeprom - get the PCB revision
+ *
+ * Read the EEPROM to determine the board revision.
+ *
+ * This function is called before relocation, so we need to read a private
+ * copy of the EEPROM into a local variable on the stack.
+ */
+u8 get_pcb_revision_from_eeprom(void)
+{
+	struct __attribute__ ((__packed__)) board_eeprom {
+		u8 magic[MAGIC_NUMBER_BYTES];
+		u8 format_ver;
+		u16 product_id;
+		u8 pcb_revision;
+	} be;
+
+	int ret;
+	struct udevice *dev;
+
+	ret = i2c_get_chip_for_busnum(CONFIG_SYS_EEPROM_BUS_NUM,
+				      CONFIG_SYS_I2C_EEPROM_ADDR,
+				      1,
+				      &dev);
+
+	if (!ret)
+		dm_i2c_read(dev, 0, (void *)&be,
+			    sizeof(struct board_eeprom));
+
+	return be.pcb_revision;
+}