sunxi: armv8: fel: move fel_stash variable to the front

To return a 64-bit Allwinner chip back to the 32-bit BootROM code, we
have some embedded AArch32 code that restores the CPU state, before
branching back to the BootROM. At the moment the pointer to the buffer
with that state is located *after* the code, which makes the PC relative
code fragile: adding or removing instructions will change the distance
to that pointer variable.
The "new" Allwinner A523 SoC requires more state to be restored (GICv3
system registers), but we must do that *only* on that SoC. Conditional
compilation sounds like the easiest solution, but would mean that the
distance to that pointer would change.

Solve this rather easily by moving the pointer to the *front* of the
code: we load that pointer in the first instruction, so the distance
would always stay the same. Later in the code we won't need PC relative
addressing anymore, so this code can grow or shrink easily, for instance
due to conditional compilation.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>

diff --git a/arch/arm/cpu/armv8/fel_utils.S b/arch/arm/cpu/armv8/fel_utils.S
index 939869b..f7707ac 100644 (file)
--- a/arch/arm/cpu/armv8/fel_utils.S
+++ b/arch/arm/cpu/armv8/fel_utils.S
@@ -63,9 +63,12 @@ ENTRY(return_to_fel)
 1:     wfi
        b       1b
 
+fel_stash_addr:                        // must immediately precede back_in_32:
+       .word   0x00000000      // receives fel_stash addr, by AA64 code above
+
 /* AArch32 code to restore the state from fel_stash and return back to FEL. */
 back_in_32:
-       .word   0xe59f0028      // ldr  r0, [pc, #40]   ; load fel_stash address
+       .word   0xe51f000c      // ldr  r0, [pc, #-12]  ; load fel_stash address
        .word   0xe5901008      // ldr  r1, [r0, #8]
        .word   0xe129f001      // msr  CPSR_fc, r1
        .word   0xf57ff06f      // isb
@@ -77,6 +80,4 @@ back_in_32:
        .word   0xee011f10      // mcr  15, 0, r1, cr1, cr0, {0}  ; SCTLR
        .word   0xf57ff06f      // isb
        .word   0xe12fff1e      // bx   lr              ; return to FEL
-fel_stash_addr:
-       .word   0x00000000      // receives fel_stash addr, by AA64 code above
 ENDPROC(return_to_fel)