s390/boot: Improve decompression error reporting

Currently, decompression error messages can be very uninformative:
[    0.029853] startup: read error
[    0.040507] startup:  -- System halted

Improve these messages to make it clear that the error originates from
the decompression code. Additionally, on decompression failures, if
bootdebug is enabled, dump the message ring buffer before halting. This
provides more context for diagnosing startup issues.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/boot/decompressor.c

@@ -9,6 +9,7 @@
 
 #include <linux/kernel.h>
 #include <linux/string.h>
+#include <asm/boot_data.h>
 #include <asm/page.h>
 #include "decompressor.h"
 #include "boot.h"
@@ -63,6 +64,15 @@ static unsigned long free_mem_end_ptr = (unsigned long) _end + BOOT_HEAP_SIZE;
 #include "../../../../lib/decompress_unzstd.c"
 #endif
 
+static void decompress_error(char *m)
+{
+	if (bootdebug)
+		boot_rb_dump();
+	boot_emerg("Decompression error: %s\n", m);
+	boot_emerg(" -- System halted\n");
+	disabled_wait();
+}
+
 unsigned long mem_safe_offset(void)
 {
 	return ALIGN(free_mem_end_ptr, PAGE_SIZE);
@@ -71,5 +81,5 @@ unsigned long mem_safe_offset(void)
 void deploy_kernel(void *output)
 {
 	__decompress(_compressed_start, _compressed_end - _compressed_start,
-		     NULL, NULL, output, vmlinux.image_size, NULL, error);
+		     NULL, NULL, output, vmlinux.image_size, NULL, decompress_error);
 }