acpi: consider XSDT in acpi_find_table()

The RSDT table is deprecated and does not exist on all systems.

By preference scan XSDT for the table to find. If no XSDT table exists, try
to use the RSDT table.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

lib/acpi/acpi.c

@@ -16,18 +16,30 @@ struct acpi_table_header *acpi_find_table(const char *sig)
 {
 	struct acpi_rsdp *rsdp;
 	struct acpi_rsdt *rsdt;
+	struct acpi_xsdt *xsdt;
 	int len, i, count;
 
 	rsdp = map_sysmem(gd_acpi_start(), 0);
 	if (!rsdp)
 		return NULL;
-	rsdt = map_sysmem(rsdp->rsdt_address, 0);
-	len = rsdt->header.length - sizeof(rsdt->header);
-	count = len / sizeof(u32);
+	if (rsdp->xsdt_address) {
+		xsdt = map_sysmem(rsdp->xsdt_address, 0);
+		len = xsdt->header.length - sizeof(xsdt->header);
+		count = len / sizeof(u64);
+	} else {
+		if (!rsdp->rsdt_address)
+			return NULL;
+		rsdt = map_sysmem(rsdp->rsdt_address, 0);
+		len = rsdt->header.length - sizeof(rsdt->header);
+		count = len / sizeof(u32);
+	}
 	for (i = 0; i < count; i++) {
 		struct acpi_table_header *hdr;
 
-		hdr = map_sysmem(rsdt->entry[i], 0);
+		if (rsdp->xsdt_address)
+			hdr = map_sysmem(xsdt->entry[i], 0);
+		else
+			hdr = map_sysmem(rsdt->entry[i], 0);
 		if (!memcmp(hdr->signature, sig, ACPI_NAME_LEN))
 			return hdr;
 		if (!memcmp(hdr->signature, "FACP", ACPI_NAME_LEN)) {