ath79: lzma-loader: allow setting custom kernel magic

...and max flash offset

The mtdsplit parser was recently refactored
to allow the kernel to have custom image header magic.

Let's also do this for the lzma-loader

For example:
When implemented together,
this allows the kernel to "appear" to be a rootfs
by OEM software in order to write an image
that is actually kernel + rootfs.

At the same time,
it would boot to openwrt normally
by setting the same magic in DTS.

Both of the variables
have a default value that is unchanged
when not defined in the makefiles

This has no effect on the size of the loader
when lzma compressed.

Signed-off-by: Michael Pratt <mcpratt@pm.me>
(cherry picked from commit 1b8bd17c2d)

target/linux/ath79/image/Makefile

@@ -4,6 +4,7 @@ include $(INCLUDE_DIR)/image.mk
 KERNEL_LOADADDR = 0x80060000
 
 DEVICE_VARS += LOADER_FLASH_OFFS LOADER_TYPE
+DEVICE_VARS += LOADER_FLASH_MAX LOADER_KERNEL_MAGIC
 DEVICE_VARS += NETGEAR_BOARD_ID NETGEAR_HW_ID
 DEVICE_VARS += RAS_BOARD RAS_ROOTFS_SIZE RAS_VERSION
 
@@ -30,7 +31,10 @@ define Build/loader-kernel
 endef
 
 define Build/loader-okli-compile
-	$(call Build/loader-common,FLASH_OFFS=$(LOADER_FLASH_OFFS) FLASH_MAX=0)
+	$(call Build/loader-common, \
+		FLASH_OFFS=$(LOADER_FLASH_OFFS) \
+		FLASH_MAX=$(LOADER_FLASH_MAX) \
+		KERNEL_MAGIC=$(LOADER_KERNEL_MAGIC) )
 endef
 
 # Arguments: <output name> <kernel offset>

target/linux/ath79/image/lzma-loader/Makefile

@@ -13,6 +13,7 @@ LOADADDR	:= 0x80060000
 LOADER		:= loader.bin
 LOADER_NAME	:= $(basename $(notdir $(LOADER)))
 LOADER_DATA	:=
+KERNEL_MAGIC	:=
 TARGET_DIR	:=
 FLASH_OFFS	:=
 FLASH_MAX	:=
@@ -41,6 +42,7 @@ loader-compile: $(PKG_BUILD_DIR)/.prepared
 		LZMA_TEXT_START=$(LZMA_TEXT_START) \
 		LOADADDR=$(LOADADDR) \
 		LOADER_DATA=$(LOADER_DATA) \
+		KERNEL_MAGIC=$(KERNEL_MAGIC) \
 		FLASH_OFFS=$(FLASH_OFFS) \
 		FLASH_MAX=$(FLASH_MAX) \
 		BOARD="$(BOARD)" \

target/linux/ath79/image/lzma-loader/src/Makefile

@@ -18,6 +18,7 @@
 LOADADDR	:=
 LZMA_TEXT_START	:= 0x80a00000
 LOADER_DATA	:=
+KERNEL_MAGIC	:=
 BOARD		:=
 FLASH_OFFS	:=
 FLASH_MAX	:=
@@ -54,6 +55,10 @@ OBJECTS		+= data.o
 CFLAGS		+= -DLZMA_WRAPPER=1 -DLOADADDR=$(LOADADDR)
 endif
 
+ifneq ($(strip $(KERNEL_MAGIC)),)
+CFLAGS		+= -DCONFIG_KERNEL_MAGIC=$(KERNEL_MAGIC)
+endif
+
 ifneq ($(strip $(KERNEL_CMDLINE)),)
 CFLAGS		+= -DCONFIG_KERNEL_CMDLINE='"$(KERNEL_CMDLINE)"'
 endif

target/linux/ath79/image/lzma-loader/src/loader.c

@@ -189,7 +189,11 @@ static void lzma_init_data(void)
 
 		p = flash_base + flash_ofs;
 		magic = get_be32(p);
+#ifdef CONFIG_KERNEL_MAGIC
+		if (magic == CONFIG_KERNEL_MAGIC) {
+#else
 		if (magic == IH_MAGIC_OKLI) {
+#endif
 			hdr = (struct image_header *) p;
 			break;
 		}