MIPS: fix ROM exception vectors
When booting from ROM, early exceptions can't be handled
properly. Instead of busy-looping give the developer the
possibilty to examine the situation. Invoke an UHI
exception operation which can be read as unhandled exception
by a hardware debugger if one is attached. If the debugger
doesn't support UHI, the exception is read as unexpected
breakpoint.
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/arch/mips/cpu/start.S b/arch/mips/cpu/start.S
index 108d2df..2397b6c 100644
--- a/arch/mips/cpu/start.S
+++ b/arch/mips/cpu/start.S
@@ -52,6 +52,14 @@
.set noreorder
+ .macro uhi_mips_exception
+ move k0, t9 # preserve t9 in k0
+ move k1, a0 # preserve a0 in k1
+ li t9, 15 # UHI exception operation
+ li a0, 0 # Use hard register context
+ sdbbp 1 # Invoke UHI operation
+ .endm
+
ENTRY(_start)
/* U-Boot entry point */
b reset
@@ -79,30 +87,30 @@
#endif
#if defined(CONFIG_ROM_EXCEPTION_VECTORS)
+ /*
+ * Exception vector entry points. When running from ROM, an exception
+ * cannot be handled. Halt execution and transfer control to debugger,
+ * if one is attached.
+ */
.org 0x200
/* TLB refill, 32 bit task */
-1: b 1b
- nop
+ uhi_mips_exception
.org 0x280
/* XTLB refill, 64 bit task */
-1: b 1b
- nop
+ uhi_mips_exception
.org 0x300
/* Cache error exception */
-1: b 1b
- nop
+ uhi_mips_exception
.org 0x380
/* General exception */
-1: b 1b
- nop
+ uhi_mips_exception
.org 0x400
/* Catch interrupt exceptions */
-1: b 1b
- nop
+ uhi_mips_exception
.org 0x480
/* EJTAG debug exception */
@@ -222,6 +230,7 @@
move a0, zero # a0 <-- boot_flags = 0
PTR_LA t9, board_init_f
+
jr t9
move ra, zero