part: extract MBR signature from partitions

EFI client programs need the signature information from the partition
table to determine the disk a partition is on, so we need to fill that
in here.

Signed-off-by: Peter Jones <pjones@redhat.com>
[separated from efi_loader part, and fixed build-errors for non-
 CONFIG_EFI_PARTITION case]
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

include/blk.h

@@ -8,6 +8,8 @@
 #ifndef BLK_H
 #define BLK_H
 
+#include <efi.h>
+
 #ifdef CONFIG_SYS_64BIT_LBA
 typedef uint64_t lbaint_t;
 #define LBAFlength "ll"
@@ -40,6 +42,17 @@ enum if_type {
 #define BLK_PRD_SIZE		20
 #define BLK_REV_SIZE		8
 
+/*
+ * Identifies the partition table type (ie. MBR vs GPT GUID) signature
+ */
+enum sig_type {
+	SIG_TYPE_NONE,
+	SIG_TYPE_MBR,
+	SIG_TYPE_GUID,
+
+	SIG_TYPE_COUNT			/* Number of signature types */
+};
+
 /*
  * With driver model (CONFIG_BLK) this is uclass platform data, accessible
  * with dev_get_uclass_platdata(dev)
@@ -67,6 +80,11 @@ struct blk_desc {
 	char		vendor[BLK_VEN_SIZE + 1]; /* device vendor string */
 	char		product[BLK_PRD_SIZE + 1]; /* device product number */
 	char		revision[BLK_REV_SIZE + 1]; /* firmware revision */
+	enum sig_type	sig_type;	/* Partition table signature type */
+	union {
+		uint32_t mbr_sig;	/* MBR integer signature */
+		efi_guid_t guid_sig;	/* GPT GUID Signature */
+	};
 #if CONFIG_IS_ENABLED(BLK)
 	/*
 	 * For now we have a few functions which take struct blk_desc as a