[POWERPC] 4xx: Add early udbg support for 40x processors

This adds some basic real mode based early udbg support for 40x
in order to debug things more easily

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
index ea1137851a4a..be09f0d2d90b 100644
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -206,6 +206,45 @@ _GLOBAL(_nmask_and_or_msr)
         isync
         blr                     /* Done */
 
+#ifdef CONFIG_40x
+
+/*
+ * Do an IO access in real mode
+ */
+_GLOBAL(real_readb)
+        mfmsr   r7
+        ori     r0,r7,MSR_DR
+        xori    r0,r0,MSR_DR
+        sync
+        mtmsr   r0
+        sync
+        isync
+        lbz     r3,0(r3)
+        sync
+        mtmsr   r7
+        sync
+        isync
+        blr
+
+        /*
+ * Do an IO access in real mode
+ */
+_GLOBAL(real_writeb)
+        mfmsr   r7
+        ori     r0,r7,MSR_DR
+        xori    r0,r0,MSR_DR
+        sync
+        mtmsr   r0
+        sync
+        isync
+        stb     r3,0(r4)
+        sync
+        mtmsr   r7
+        sync
+        isync
+        blr
+
+#endif /* CONFIG_40x */
 
 /*
  * Flush MMU TLB