microblaze: Final support for statically linked DTB

If r7 is zero at kernel boot, or does not point to a valid DTB, then
we fall back to a DTB (assumed to be) linked statically in the kernel, instead
of blindly copying bogus cruft into the kernel DTB memory region

Signed-off-by: John Williams <john.williams@petalogix.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>

1 files changed, 11 insertions, 4 deletions

diff --git a/arch/microblaze/kernel/head.S b/arch/microblaze/kernel/head.S
index e568d6ec621b..815bcaae99c3 100644
--- a/arch/microblaze/kernel/head.S
+++ b/arch/microblaze/kernel/head.S
@@ -31,6 +31,7 @@
 #include <linux/linkage.h>
 #include <asm/thread_info.h>
 #include <asm/page.h>
+#include <asm/prom.h>           /* for OF_DT_HEADER */
 
 #ifdef CONFIG_MMU
 #include <asm/setup.h> /* COMMAND_LINE_SIZE */
@@ -54,11 +55,16 @@ ENTRY(_start)
         andi    r1, r1, ~2
         mts     rmsr, r1
 
-/* save fdt to kernel location */
-/* r7 stores pointer to fdt blob */
-        beqi    r7, no_fdt_arg
+/* r7 may point to an FDT, or there may be one linked in.
+   if it's in r7, we've got to save it away ASAP.
+   We ensure r7 points to a valid FDT, just in case the bootloader
+   is broken or non-existent */
+        beqi    r7, no_fdt_arg                  /* NULL pointer?  don't copy */
+        lw      r11, r0, r7                     /* Does r7 point to a */
+        rsubi   r11, r11, OF_DT_HEADER          /* valid FDT? */
+        bnei    r11, no_fdt_arg                 /* No - get out of here */
         or      r11, r0, r0 /* incremment */
-        ori     r4, r0, TOPHYS(_fdt_start) /* save bram context */
+        ori     r4, r0, TOPHYS(_fdt_start)
         ori     r3, r0, (0x4000 - 4)
 _copy_fdt:
         lw      r12, r7, r11 /* r12 = r7 + r11 */
@@ -67,6 +73,7 @@ _copy_fdt:
         bgtid   r3, _copy_fdt /* loop for all entries */
         addik   r3, r3, -4 /* descrement loop */
 no_fdt_arg:
+        add     r7, r0, r0                      /* Clear r7, just to be sure */
 
 #ifdef CONFIG_MMU