grub2: Specify boot partition

Since boot partition was not specified, grub tools try to detect it
automatically. This patch add an option to force it.

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/grub2/Config.in

@@ -111,6 +111,19 @@ config BR2_TARGET_GRUB2_X86_64_EFI
 
 endchoice
 
+if BR2_TARGET_GRUB2_I386_PC
+
+config BR2_TARGET_GRUB2_BOOT_PARTITION
+	string "boot partition"
+	default "hd0,msdos1"
+	help
+	  Specify the partition where the /boot/grub/grub.cfg file is
+	  located. Use 'hd0,msdos1' for the first partition of the
+	  first disk if using a legacy partition table, or 'hd0,gpt1'
+	  if using GPT partition table.
+
+endif # BR2_TARGET_GRUB2_I386_PC
+
 config BR2_TARGET_GRUB2_BUILTIN_MODULES
 	string "builtin modules"
 	default "boot linux ext2 fat part_msdos part_gpt normal biosdisk" if BR2_TARGET_GRUB2_I386_PC

boot/grub2/grub2.mk

@@ -11,9 +11,14 @@ GRUB2_LICENSE = GPLv3+
 GRUB2_LICENSE_FILES = COPYING
 GRUB2_DEPENDENCIES = host-bison host-flex
 
+GRUB2_BUILTIN_MODULES = $(call qstrip,$(BR2_TARGET_GRUB2_BUILTIN_MODULES))
+GRUB2_BUILTIN_CONFIG = $(call qstrip,$(BR2_TARGET_GRUB2_BUILTIN_CONFIG))
+GRUB2_BOOT_PARTITION = $(call qstrip,$(BR2_TARGET_GRUB2_BOOT_PARTITION))
+
 ifeq ($(BR2_TARGET_GRUB2_I386_PC),y)
 GRUB2_IMAGE = $(BINARIES_DIR)/grub.img
 GRUB2_CFG = $(TARGET_DIR)/boot/grub/grub.cfg
+GRUB2_PREFIX = ($(GRUB2_BOOT_PARTITION))/boot/grub
 GRUB2_TUPLE = i386-pc
 GRUB2_TARGET = i386
 GRUB2_PLATFORM = pc
@@ -33,9 +38,6 @@ GRUB2_TARGET = x86_64
 GRUB2_PLATFORM = efi
 endif
 
-GRUB2_BUILTIN_MODULES = $(call qstrip,$(BR2_TARGET_GRUB2_BUILTIN_MODULES))
-GRUB2_BUILTIN_CONFIG = $(call qstrip,$(BR2_TARGET_GRUB2_BUILTIN_CONFIG))
-
 # Grub2 is kind of special: it considers CC, LD and so on to be the
 # tools to build the native tools (i.e to be executed on the build
 # machine), and uses TARGET_CC, TARGET_CFLAGS, TARGET_CPPFLAGS to
@@ -71,7 +73,7 @@ define GRUB2_IMAGE_INSTALLATION
 		-d $(HOST_DIR)/usr/lib/grub/$(GRUB2_TUPLE) \
 		-O $(GRUB2_TUPLE) \
 		-o $(GRUB2_IMAGE) \
-		$(if $(GRUB2_PREFIX),-p $(GRUB2_PREFIX)) \
+		-p "$(GRUB2_PREFIX)" \
 		$(if $(GRUB2_BUILTIN_CONFIG),-c $(GRUB2_BUILTIN_CONFIG)) \
 		$(GRUB2_BUILTIN_MODULES)
 	mkdir -p $(dir $(GRUB2_CFG))