efi_loader: Add distro boot script for removable media

UEFI defines a simple boot protocol for removable media. There we should look
at the EFI (first GPT FAT) partition and search for /efi/boot/bootXXX.efi with
XXX being different between different platforms (x86, x64, arm, aa64, ...).

This patch implements a simple version of that protocol for the default distro
boot script. With this we can automatically boot from valid UEFI enabled
removable media.

Because from all I could see U-Boot by default doesn't deliver device tree
blobs with its firmware, we also need to load the dtb from somewhere. Traverse
the same EFI partition for an fdt file that fits our current board so that
an OS receives a valid device tree when booted automatically.
Signed-off-by: NAlexander Graf <agraf@suse.de>
Reviewed-by: NSimon Glass <sjg@chromium.org>

include/config_distro_bootcmd.h

@@ -90,6 +90,48 @@
 	BOOT_TARGET_DEVICES_references_UBIFS_without_CONFIG_CMD_UBIFS
 #endif
 
+#ifdef CONFIG_EFI_LOADER
+#if defined(CONFIG_ARM64)
+#define BOOTEFI_NAME "bootaa64.efi"
+#elif defined(CONFIG_ARM)
+#define BOOTEFI_NAME "bootarm.efi"
+#endif
+#endif
+
+#ifdef BOOTEFI_NAME
+#define BOOTENV_SHARED_EFI                                                \
+	"boot_efi_binary="                                                \
+		"load ${devtype} ${devnum}:${distro_bootpart} "           \
+			"${kernel_addr_r} efi/boot/"BOOTEFI_NAME"; "      \
+		"bootefi ${kernel_addr_r}\0"                              \
+	\
+	"load_efi_dtb="                                                   \
+		"load ${devtype} ${devnum}:${distro_bootpart} "           \
+			"${fdt_addr_r} ${prefix}${fdt_name}; "           \
+		"fdt addr ${fdt_addr_r}\0"                                \
+	\
+	"efi_dtb_prefixes=/ /dtb/ /dtb/current/\0"                        \
+	"scan_dev_for_efi="                                               \
+		"for prefix in ${efi_dtb_prefixes}; do "                  \
+			"if test -e ${devtype} "                          \
+					"${devnum}:${distro_bootpart} "   \
+					"${prefix}${fdt_name}; then "     \
+				"run load_efi_dtb; "                      \
+			"fi;"                                             \
+		"done;"                                                   \
+		"if test -e ${devtype} ${devnum}:${distro_bootpart} "     \
+					"efi/boot/"BOOTEFI_NAME"; then "  \
+				"echo Found EFI removable media binary "  \
+					"efi/boot/"BOOTEFI_NAME"; "       \
+				"run boot_efi_binary; "                   \
+				"echo EFI LOAD FAILED: continuing...; "   \
+		"fi; \0"
+#define SCAN_DEV_FOR_EFI "run scan_dev_for_efi;"
+#else
+#define BOOTENV_SHARED_EFI
+#define SCAN_DEV_FOR_EFI
+#endif
+
 #ifdef CONFIG_CMD_SATA
 #define BOOTENV_SHARED_SATA	BOOTENV_SHARED_BLKDEV(sata)
 #define BOOTENV_DEV_SATA	BOOTENV_DEV_BLKDEV
@@ -217,6 +259,7 @@
 	BOOTENV_SHARED_SCSI \
 	BOOTENV_SHARED_IDE \
 	BOOTENV_SHARED_UBIFS \
+	BOOTENV_SHARED_EFI \
 	"boot_prefixes=/ /boot/\0" \
 	"boot_scripts=boot.scr.uimg boot.scr\0" \
 	"boot_script_dhcp=boot.scr.uimg\0" \
@@ -258,7 +301,9 @@
 		"for prefix in ${boot_prefixes}; do "                     \
 			"run scan_dev_for_extlinux; "                     \
 			"run scan_dev_for_scripts; "                      \
-		"done\0"                                                  \
+		"done;"                                                   \
+		SCAN_DEV_FOR_EFI                                          \
+		"\0"                                                      \
 	\
 	"scan_dev_for_boot_part="                                         \
 		"part list ${devtype} ${devnum} -bootable devplist; "     \