mips: start.S: Add Octeon boot header compatibility

Octeon has a specific boot header, when booted via SPI NOR, NAND or MMC.
Here the only 2 instructions are allowed in the first few bytes of the
image. And these instructions need to be one branch and a nop. This
patch adds the necessary nop after the nop, to that the common MIPS
image is compatible with this Octeon header.

The tool to patch the Octeon boot header into the image will be send in
a follow-up patch.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Aaron Williams <awilliams@marvell.com>
Cc: Chandrakala Chavva <cchavva@marvell.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

diff --git a/arch/mips/cpu/start.S b/arch/mips/cpu/start.S
index d0c4122..335aafa 100644 (file)
--- a/arch/mips/cpu/start.S
+++ b/arch/mips/cpu/start.S
@@ -74,9 +74,14 @@
        .endm
 
 ENTRY(_start)
-       /* U-Boot entry point */
+       /*
+        * U-Boot entry point.
+        * Do not add instructions to the branch delay slot! Some SoC's
+        * like Octeon might patch the final U-Boot binary at this location
+        * with additional boot headers.
+        */
        b       reset
-        mtc0   zero, CP0_COUNT # clear cp0 count for most accurate boot timing
+        nop
 
 #if defined(CONFIG_MIPS_INSERT_BOOT_CONFIG)
        /*
@@ -123,6 +128,7 @@ ENTRY(_start)
 #endif
 
 reset:
+       mtc0    zero, CP0_COUNT # clear cp0 count for most accurate boot timing
 #if __mips_isa_rev >= 6
        mfc0    t0, CP0_CONFIG, 5
        and     t0, t0, MIPS_CONF5_VP