riscv: boot: add Image.xz support

The Image.* targets existed for other compressors already.  Bootloader
support is needed for decompression.

This is for CONFIG_EFI_ZBOOT=n. With CONFIG_EFI_ZBOOT=y, XZ was already
available.

Comparision with Linux 6.10 RV64GC tinyconfig (in KiB):

    1027 Image
     594 Image.gz
     541 Image.zst
     510 Image.lzma
     474 Image.xz

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Lasse Collin <[email protected]>
Reviewed-by: Emil Renner Berthing <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Jules Maselbas <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Joel Stanley <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Jubin Zhong <[email protected]>
Cc: Krzysztof Kozlowski <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Rui Li <[email protected]>
Cc: Sam James <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Larhzu

arch/riscv/Kconfig

@@ -156,6 +156,7 @@ config RISCV
 	select HAVE_KERNEL_LZO if !XIP_KERNEL && !EFI_ZBOOT
 	select HAVE_KERNEL_UNCOMPRESSED if !XIP_KERNEL && !EFI_ZBOOT
 	select HAVE_KERNEL_ZSTD if !XIP_KERNEL && !EFI_ZBOOT
+	select HAVE_KERNEL_XZ if !XIP_KERNEL && !EFI_ZBOOT
 	select HAVE_KPROBES if !XIP_KERNEL
 	select HAVE_KRETPROBES if !XIP_KERNEL
 	# https://github.com/ClangBuiltLinux/linux/issues/1881

arch/riscv/Makefile

@@ -159,6 +159,7 @@ boot-image-$(CONFIG_KERNEL_LZ4)		:= Image.lz4
 boot-image-$(CONFIG_KERNEL_LZMA)	:= Image.lzma
 boot-image-$(CONFIG_KERNEL_LZO)		:= Image.lzo
 boot-image-$(CONFIG_KERNEL_ZSTD)	:= Image.zst
+boot-image-$(CONFIG_KERNEL_XZ)		:= Image.xz
 ifdef CONFIG_RISCV_M_MODE
 boot-image-$(CONFIG_ARCH_CANAAN)	:= loader.bin
 endif
@@ -183,12 +184,12 @@ endif
 vdso-install-y			+= arch/riscv/kernel/vdso/vdso.so.dbg
 vdso-install-$(CONFIG_COMPAT)	+= arch/riscv/kernel/compat_vdso/compat_vdso.so.dbg
 
-BOOT_TARGETS := Image Image.gz Image.bz2 Image.lz4 Image.lzma Image.lzo Image.zst loader loader.bin xipImage vmlinuz.efi
+BOOT_TARGETS := Image Image.gz Image.bz2 Image.lz4 Image.lzma Image.lzo Image.zst Image.xz loader loader.bin xipImage vmlinuz.efi
 
 all:	$(notdir $(KBUILD_IMAGE))
 
 loader.bin: loader
-Image.gz Image.bz2 Image.lz4 Image.lzma Image.lzo Image.zst loader xipImage vmlinuz.efi: Image
+Image.gz Image.bz2 Image.lz4 Image.lzma Image.lzo Image.zst Image.xz loader xipImage vmlinuz.efi: Image
 
 $(BOOT_TARGETS): vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
@@ -225,6 +226,7 @@ define archhelp
   echo  '  Image.lzma	- Compressed kernel image (arch/riscv/boot/Image.lzma)'
   echo  '  Image.lzo	- Compressed kernel image (arch/riscv/boot/Image.lzo)'
   echo  '  Image.zst	- Compressed kernel image (arch/riscv/boot/Image.zst)'
+  echo  '  Image.xz	- Compressed kernel image (arch/riscv/boot/Image.xz)'
   echo  '  vmlinuz.efi	- Compressed EFI kernel image (arch/riscv/boot/vmlinuz.efi)'
   echo  '		  Default when CONFIG_EFI_ZBOOT=y'
   echo  '  xipImage	- Execute-in-place kernel image (arch/riscv/boot/xipImage)'

arch/riscv/boot/Makefile

@@ -64,6 +64,9 @@ $(obj)/Image.lzo: $(obj)/Image FORCE
 $(obj)/Image.zst: $(obj)/Image FORCE
 	$(call if_changed,zstd)
 
+$(obj)/Image.xz: $(obj)/Image FORCE
+	$(call if_changed,xzkern)
+
 $(obj)/loader.bin: $(obj)/loader FORCE
 	$(call if_changed,objcopy)