utils/hwstub: make stmp stub able to load in a MMU'ed environement

In might be useful to load hwstub in an environment with the MMU active,
in which case care must be taken on the order in which things are done.
Mostly, one should not disable the MMU before moving stuff around. The code
assumes the linking address (0 currently) is identity mapped.

Change-Id: I8d54ce9e8cadcde2e08990353ca7a46803731ca7

1 files changed, 10 insertions, 6 deletions

diff --git a/utils/hwstub/stub/stmp/crt0.S b/utils/hwstub/stub/stmp/crt0.S
index f4a0c28360..38b6f18ac5 100644
--- a/utils/hwstub/stub/stmp/crt0.S
+++ b/utils/hwstub/stub/stmp/crt0.S
@@ -5,12 +5,10 @@
 start:
     sub     r7, pc, #8 /* Copy running address */
     msr     cpsr_c, #0xd3 /* enter supervisor mode, disable IRQ/FIQ */
-    /* Disable MMU, disable caching and buffering;
-     * use low exception range address */
-    mrc     p15, 0, r0, c1, c0, 0
-    ldr     r1, =0x3005
-    bic     r0, r1
-    mcr     p15, 0, r0, c1, c0, 0
+    /* The stub could be located at a virtual address so killing the MMU at
+     * this point would be mere suicide. We assume that the remap location
+     * is identically mapped and kill the MMU after the copy */
+
     /* Relocate to right address */
     mov    r2, r7
     ldr    r3, =_copystart
@@ -25,6 +23,12 @@ start:
     /* Jump to real location */
     ldr     pc, =remap
 remap:
+    /* Disable MMU, disable caching and buffering;
+     * use low exception range address */
+    mrc     p15, 0, r0, c1, c0, 0
+    ldr     r1, =0x3005
+    bic     r0, r1
+    mcr     p15, 0, r0, c1, c0, 0
     /* clear bss */
     ldr     r2, =bss_start
     ldr     r3, =bss_end