ARM: implement "uncompressed zImage"

Based on RFC patch by Uwe Kleine-König
http://www.spinics.net/lists/arm-kernel/msg230153.html

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -71,6 +71,7 @@ compress-$(CONFIG_KERNEL_LZO)  = lzo
 compress-$(CONFIG_KERNEL_LZMA) = lzma
 compress-$(CONFIG_KERNEL_XZ)   = xzkern
 compress-$(CONFIG_KERNEL_LZ4)  = lz4
+compress-$(CONFIG_KERNEL_CAT)  = cat
 
 # Borrowed libfdt files for the ATAG compatibility mode
 
--- a/arch/arm/boot/compressed/decompress.c
+++ b/arch/arm/boot/compressed/decompress.c
@@ -55,6 +55,10 @@ extern char * strstr(const char * s1, co
 #include "../../../../lib/decompress_unlz4.c"
 #endif
 
+#ifdef CONFIG_KERNEL_CAT
+#include "../../../../lib/decompress_uncat.c"
+#endif
+
 int do_decompress(u8 *input, int len, u8 *output, void (*error)(char *x))
 {
 	return __decompress(input, len, NULL, NULL, output, 0, NULL, error);
--- /dev/null
+++ b/arch/arm/boot/compressed/piggy.cat.S
@@ -0,0 +1,6 @@
+	.section .piggydata,#alloc
+	.globl	input_data
+input_data:
+	.incbin	"arch/arm/boot/compressed/piggy.cat"
+	.globl	input_data_end
+input_data_end:
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -127,6 +127,9 @@ config HAVE_KERNEL_LZO
 config HAVE_KERNEL_LZ4
 	bool
 
+config HAVE_KERNEL_CAT
+	bool
+
 choice
 	prompt "Kernel compression mode"
 	default KERNEL_GZIP
@@ -193,9 +196,10 @@ config KERNEL_LZO
 	bool "LZO"
 	depends on HAVE_KERNEL_LZO
 	help
-	  Its compression ratio is the poorest among the choices. The kernel
-	  size is about 10% bigger than gzip; however its speed
-	  (both compression and decompression) is the fastest.
+	  Its compression ratio is the poorest among the choices (apart from
+	  uncompressed below). The kernel size is about 10% bigger than gzip;
+	  however its speed (both compression and decompression) is the
+	  fastest.
 
 config KERNEL_LZ4
 	bool "LZ4"
@@ -209,6 +213,12 @@ config KERNEL_LZ4
 	  is about 8% bigger than LZO. But the decompression speed is
 	  faster than LZO.
 
+config KERNEL_CAT
+	bool "uncompressed"
+	depends on HAVE_KERNEL_CAT
+	help
+	  Don't use compression at all.
+
 endchoice
 
 config DEFAULT_HOSTNAME
--- /dev/null
+++ b/lib/decompress_uncat.c
@@ -0,0 +1,17 @@
+#include <linux/types.h>
+#include <linux/compiler.h>
+
+#ifdef STATIC
+
+STATIC int __decompress(unsigned char *buf, long in_len,
+			long (*fill)(void*, unsigned long),
+			long (*flush)(void*, unsigned long),
+			unsigned char *output, long out_len,
+			long *posp,
+			void (*error)(char *x))
+{
+	memmove(output, buf, in_len);
+	return 0;
+}
+
+#endif
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -357,6 +357,13 @@ cmd_lz4 = (cat $(filter-out FORCE,$^) |
 	lz4c -l -c1 stdin stdout && $(call size_append, $(filter-out FORCE,$^))) > $@ || \
 	(rm -f $@ ; false)
 
+# uncompressed
+# ---------------------------------------------------------------------------
+quiet_cmd_cat = CAT     $@
+cmd_cat = (cat $(filter-out FORCE,$^) \
+	&& $(call size_append, $(filter-out FORCE,$^))) > $@ || \
+	(rm -f $@ ; false)
+
 # U-Boot mkimage
 # ---------------------------------------------------------------------------
 
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -65,6 +65,7 @@ config ARM
 	select HAVE_KERNEL_LZMA
 	select HAVE_KERNEL_LZO
 	select HAVE_KERNEL_XZ
+	select HAVE_KERNEL_CAT
 	select HAVE_KPROBES if !XIP_KERNEL && !CPU_ENDIAN_BE32 && !CPU_V7M
 	select HAVE_KRETPROBES if (HAVE_KPROBES)
 	select HAVE_MEMBLOCK