powerpc/powernv: Support for OPAL console

This adds a udbg and an hvc console backend for supporting a console
using the OPAL console interfaces.

On OPAL v1 we have hvc0 mapped to whatever console the system was
configured for (network or hvsi serial port) via the service
processor.

On OPAL v2 we have hvcN mapped to the Nth console provided by OPAL
which generally corresponds to:

	hvc0 : network console (raw protocol)
	hvc1 : serial port S1 (hvsi)
	hvc2 : serial port S2 (hvsi)

Note: At this point, early debug console only works with OPAL v1
and shouldn't be enabled in a normal kernel.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index dea8191253d2..06c7251c1bf7 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -53,7 +53,8 @@
  *   2. The kernel is entered at __start
  * -or- For OPAL entry:
  *   1. The MMU is off, processor in HV mode, primary CPU enters at 0
- *      with device-tree in gpr3
+ *      with device-tree in gpr3. We also get OPAL base in r8 and
+ *      entry in r9 for debugging purposes
  *   2. Secondary processors enter at 0x60 with PIR in gpr3
  *
  *  For iSeries:
@@ -335,6 +336,11 @@ _GLOBAL(__start_initialization_multiplatform)
         /* Save parameters */
         mr      r31,r3
         mr      r30,r4
+#ifdef CONFIG_PPC_EARLY_DEBUG_OPAL
+        /* Save OPAL entry */
+        mr      r28,r8
+        mr      r29,r9
+#endif
 
 #ifdef CONFIG_PPC_BOOK3E
         bl      .start_initialization_book3e
@@ -711,6 +717,12 @@ _INIT_STATIC(start_here_multiplatform)
         bdnz    3b
 4:
 
+#ifdef CONFIG_PPC_EARLY_DEBUG_OPAL
+        /* Setup OPAL entry */
+        std     r28,0(r11);
+        std     r29,8(r11);
+#endif
+
 #ifndef CONFIG_PPC_BOOK3E
         mfmsr   r6
         ori     r6,r6,MSR_RI