[MIPS] Probe initrd header only if explicitly specified

Currently init_initrd() probes initrd header at the last page of kernel
image, but it is valid only if addinitrd was used.  If addinitrd was not
used, the area contains garbage so probing there might misdetect initrd
header (magic number is not strictly robust).

This patch introduces CONFIG_PROBE_INITRD_HEADER to explicitly enable this
probing.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -1886,6 +1886,15 @@ config STACKTRACE_SUPPORT
 
 source "init/Kconfig"
 
+config PROBE_INITRD_HEADER
+	bool "Probe initrd header created by addinitrd"
+	depends on BLK_DEV_INITRD
+	help
+	  Probe initrd header at the last page of kernel image.
+	  Say Y here if you are using arch/mips/boot/addinitrd.c to
+	  add initrd or initramfs image to the kernel image.
+	  Otherwise, say N.
+
 menu "Bus options (PCI, PCMCIA, EISA, ISA, TC)"
 
 config HW_HAS_EISA

arch/mips/kernel/setup.c

@@ -160,30 +160,33 @@ early_param("rd_size", rd_size_early);
 static unsigned long __init init_initrd(void)
 {
 	unsigned long end;
-	u32 *initrd_header;
 
 	/*
 	 * Board specific code or command line parser should have
 	 * already set up initrd_start and initrd_end. In these cases
 	 * perfom sanity checks and use them if all looks good.
 	 */
-	if (initrd_start && initrd_end > initrd_start)
-		goto sanitize;
+	if (!initrd_start || initrd_end <= initrd_start) {
+#ifdef CONFIG_PROBE_INITRD_HEADER
+		u32 *initrd_header;
 
-	/*
-	 * See if initrd has been added to the kernel image by
-	 * arch/mips/boot/addinitrd.c. In that case a header is
-	 * prepended to initrd and is made up by 8 bytes. The fisrt
-	 * word is a magic number and the second one is the size of
-	 * initrd.  Initrd start must be page aligned in any cases.
-	 */
-	initrd_header = __va(PAGE_ALIGN(__pa_symbol(&_end) + 8)) - 8;
-	if (initrd_header[0] != 0x494E5244)
+		/*
+		 * See if initrd has been added to the kernel image by
+		 * arch/mips/boot/addinitrd.c. In that case a header is
+		 * prepended to initrd and is made up by 8 bytes. The first
+		 * word is a magic number and the second one is the size of
+		 * initrd.  Initrd start must be page aligned in any cases.
+		 */
+		initrd_header = __va(PAGE_ALIGN(__pa_symbol(&_end) + 8)) - 8;
+		if (initrd_header[0] != 0x494E5244)
+			goto disable;
+		initrd_start = (unsigned long)(initrd_header + 2);
+		initrd_end = initrd_start + initrd_header[1];
+#else
 		goto disable;
-	initrd_start = (unsigned long)(initrd_header + 2);
-	initrd_end = initrd_start + initrd_header[1];
+#endif
+	}
 
-sanitize:
 	if (initrd_start & ~PAGE_MASK) {
 		pr_err("initrd start must be page aligned\n");
 		goto disable;