efi: Add functions for decoding the EFI tables

The EFI stub can pass a table to U-Boot with information about the memory map
Potentially other things will follow. Add a way to access this table.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

lib/efi/Makefile

@@ -5,6 +5,7 @@
 #
 
 obj-$(CONFIG_EFI_APP) += efi_app.o efi.o
+obj-$(CONFIG_EFI_STUB) += efi_info.o
 
 CFLAGS_REMOVE_efi_stub.o := -mregparm=3 \
 	$(if $(CONFIG_EFI_STUB_64BIT),-march=i386 -m32)

lib/efi/efi_info.c

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2015 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ *
+ * Access to the EFI information table
+ */
+
+#include <common.h>
+#include <efi.h>
+#include <errno.h>
+#include <mapmem.h>
+
+int efi_info_get(enum efi_entry_t type, void **datap, int *sizep)
+{
+	struct efi_entry_hdr *entry;
+	struct efi_info_hdr *info;
+	int ret;
+
+	if (!gd->arch.table)
+		return -ENODATA;
+
+	info = map_sysmem(gd->arch.table, 0);
+	if (info->version != EFI_TABLE_VERSION) {
+		ret = -EPROTONOSUPPORT;
+		goto err;
+	}
+
+	entry = (struct efi_entry_hdr *)((ulong)info + info->hdr_size);
+	while (entry->type != EFIET_END) {
+		if (entry->type == type) {
+			if (entry->addr)
+				*datap = map_sysmem(entry->addr, entry->size);
+			else
+				*datap = entry + 1;
+			*sizep = entry->size;
+			return 0;
+		}
+		entry = (struct efi_entry_hdr *)((ulong)entry + entry->link);
+	}
+
+	ret = -ENOENT;
+err:
+	unmap_sysmem(info);
+
+	return ret;
+}