efiwrapper: find rsdp in ebda area

Per ACPI spec (5.2.5.1 Finding the RSDP on IA-PC Systems), OSPM could find RSDP
by searching physical memory ranges on 16-byte boundaries at "The first 1 KB of
 the Extended BIOS Data Area (EBDA). For EISA or MCA systems, the EBDA can
be found in the two-byte location 40:0Eh on the BIOS data area."

Although EBDA is deprecated on modern UEFI platform, but it could exist on some
virtualization platfroms. Since ACPI RSDP info is not supported by multiboot
protocol so it might get lost by searching 0xe0000~0x100000 area only.

Tracked-On: OAM-111350
Signed-off-by: Victor Sun <victor.sun@intel.com>
Signed-off-by: Zhang Chen <chen.zhang@intel.com>

drivers/acpi/acpi.c

@@ -98,6 +98,11 @@ static uint8_t checksum(uint8_t *buf, size_t size)
 static struct RSDP_TABLE *lookup_for_rdsp(char *from)
 {
 	char *p;
+	/*
+	 * The  0x40e stores EBDA segment address, need left shift 4 bits
+	 * to get EBDA physical address.
+	 */
+	uint16_t *ebda_seg_addr = (uint16_t *)0x40e;
 
 	if (!from)
 		from = (char *)0xE0000;
@@ -106,6 +111,11 @@ static struct RSDP_TABLE *lookup_for_rdsp(char *from)
 		if (!memcmp(p, RSDP_MAGIC, sizeof(RSDP_MAGIC)))
 			return (struct RSDP_TABLE *)p;
 
+	from = (char *)((*ebda_seg_addr) << 4);
+	for (p = from; p < (from + 0x400); p += 16)
+		if (!memcmp(p, RSDP_MAGIC, sizeof(RSDP_MAGIC)))
+			return (struct RSDP_TABLE *)p;
+
 	ewerr("ACPI:can't find RSDP\n");
 
 	return NULL;