[OpenBIOS] [PATCH 1/3] vga.fs: do not attempt to map MMIO registers more than once

[Mark Cave-Ayland]

The FreeBSD PPC bootloader attempts to reset the console causing an error
because the MMIO registers are already mapped. Add a check to ensure that
we only map them once.

Signed-off-by: Mark Cave-Ayland 
---
 drivers/vga.fs |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/vga.fs b/drivers/vga.fs
index d39b062..080edf2 100644
--- a/drivers/vga.fs
+++ b/drivers/vga.fs
@@ -233,7 +233,9 @@ headerless
 \

: qemu-vga-driver-install ( -- )
-  map-mmio vbe-init
+  mmio-addr -1 = if
+    map-mmio vbe-init
+  then
   fb-addr -1 = if
     map-fb fb-addr to frame-buffer-adr
     default-font set-font