fel-to-spl-thunk.S: Fix safety guard which checks for enabled cache

The exit code path after detecting that the cache is enabled does not
need to swap FEL stacks and backup buffers. This way we get the error
actually reported by the 'fel' tool instead of the device getting
locked up.

The thunk code refuses to work if the caches are enabled because
we don't want to deal with the instructions/data cache coherency
yet. The caches are initially in a disabled state upon activating
FEL mode on all currently known Allwinner processors.
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>

fel-to-spl-thunk.S

@@ -158,7 +158,7 @@ cache_is_unsupported:
 	movw	TMP1,      (('?' << 8) + '.')
 	movt	TMP1,      (('?' << 8) + '?')
 	str	TMP1,      [BUF1, #8]
-	b	return_to_fel
+	b	return_to_fel_noswap
 
 checksum_is_bad:
 	/* The checksum test failed, so change 'eGON.BT0' -> 'eGON.BAD' */
@@ -169,6 +169,7 @@ checksum_is_bad:
 
 return_to_fel:
 	bl	swap_all_buffers
+return_to_fel_noswap:
 	pop	{TMP1, lr}
 	msr	cpsr_c,    TMP1 /* Restore the original CPSR */
 	ldr     sp,        [sp]

fel-to-spl-thunk.h

@@ -57,7 +57,7 @@
 	0xe3032f2e, /*       e0:    movw       r2, #16174                   */
 	0xe3432f3f, /*       e4:    movt       r2, #16191                   */
 	0xe5802008, /*       e8:    str        r2, [r0, #8]                 */
-	0xea000003, /*       ec:    b          100 <return_to_fel>          */
+	0xea000004, /*       ec:    b          104 <return_to_fel_noswap>   */
 	0xe3a00000, /*       f0:    mov        r0, #0                       */
 	0xe304222e, /*       f4:    movw       r2, #16942                   */
 	0xe3442441, /*       f8:    movt       r2, #17473                   */