[bios] Fix screen clearing on buggy BIOSes

The implementation of INT 10,06 on some BIOSes (observed with both
Hyper-V and a Dell OptiPlex 7010) seems to treat %dx=0xffff as a
special value meaning "do absolutely nothing".  Fix by using
%dx=0xfefe, which should still be sufficient to cover any realistic
screen size.

Reported-by: John Clark <skyman@iastate.edu>
Tested-by: John Clark <skyman@iastate.edu>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/arch/i386/firmware/pcbios/bios_console.c b/src/arch/i386/firmware/pcbios/bios_console.c
index 25c8dad2dd0feaec69752ff8a382cad06e59f968..213ebd92cd6240ce5959cf73118fcea88c4d9a6b 100644 (file)
--- a/src/arch/i386/firmware/pcbios/bios_console.c
+++ b/src/arch/i386/firmware/pcbios/bios_console.c
@@ -97,7 +97,7 @@ static void bios_handle_ed ( unsigned int count __unused,
                                           "int $0x10\n\t"
                                           "cli\n\t" )
                               : : "a" ( 0x0600 ), "b" ( bios_attr << 8 ),
-                                  "c" ( 0 ), "d" ( 0xffff ) );
+                                  "c" ( 0 ), "d" ( 0xfefe ) );
 }
 
 /**