[POWERPC] Early serial debug support for PPC44x

This adds support for early serial debugging via the built in
port on IBM/AMCC PowerPC 44x CPUs.  It uses a bolted TLB entry in
address space 1 for the UART's mapping, allowing robust debugging both
before and after the initialization of the MMU.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/udbg_16550.c b/arch/powerpc/kernel/udbg_16550.c
index a963f657222b..7afab5bcd61a 100644
--- a/arch/powerpc/kernel/udbg_16550.c
+++ b/arch/powerpc/kernel/udbg_16550.c
@@ -191,3 +191,26 @@ void udbg_init_pas_realmode(void)
         udbg_getc_poll = NULL;
 }
 #endif /* CONFIG_PPC_MAPLE */
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_44x
+#include <platforms/44x/44x.h>
+
+static void udbg_44x_as1_putc(char c)
+{
+        if (udbg_comport) {
+                while ((as1_readb(&udbg_comport->lsr) & LSR_THRE) == 0)
+                        /* wait for idle */;
+                as1_writeb(c, &udbg_comport->thr); eieio();
+                if (c == '\n')
+                        udbg_44x_as1_putc('\r');
+        }
+}
+
+void __init udbg_init_44x_as1(void)
+{
+        udbg_comport =
+                (volatile struct NS16550 __iomem *)PPC44x_EARLY_DEBUG_VIRTADDR;
+
+        udbg_putc = udbg_44x_as1_putc;
+}
+#endif /* CONFIG_PPC_EARLY_DEBUG_44x */