[SeaBIOS] [PATCH] Enable VGA output when setting Cirrus-specific mode

[Laszlo Ersek]

This patch does the same for Cirrus as David's following patch for bochs,
originally posted under
http://www.seabios.org/pipermail/seabios/2013-February/005434.html:

Enable VGA output when settings bochs-specific mode

When used from OVMF+CSM, we got no video output. It appears that we were
  never enabling the display output except when configuring a text mode.
  Which never happens, in the OVMF+CSM case.

In my testing on RHEL-6.3 with OVMF -D CSM_ENABLE / CONFIG_CSM bios.bin /
CONFIG_QEMU vgabios.bin, using Cirrus, VESA mode 0x115 is selected (Direct
Color, 800x600x24).

According to http://www.osdever.net/FreeVGA/vga/attrreg.htm,

cirrus_switch_mode()
    stdvga_attr_mask()

currently keeps/sets the "Attribute Controller Graphics Enable" bit set in
the "Attribute Mode Control Register". When invoked from OVMF+CSM, that is
not enough however, so let's do the same as for Bochs:

stdvga_attrindex_write(0x20);

which corresponds to setting the "Palette Address Source" bit in the
"Attribute Address Register":

"This bit is set to 0 to load color values to the registers in the
  internal palette. It is set to 1 for normal operation of the attribute
  controller. [...]"

clext_set_mode()
  stdvga_set_mode() -- for regular modes
    stdvga_attrindex_write() -- existing call
  cirrus_switch_mode() -- for Cirrus modes
    stdvga_attrindex_write() -- call added by this patch

Signed-off-by: Laszlo Ersek 
---
 My motivation for using Cirrus instead of stdvga is three-fold:
 - using libvirt on RHEL-6.3, Cirrus seems to be the default video card
   for the guests I tend to create,
 - it provides better max resolution in the Fedora 18 guest,
 - for some reason (maybe due to kernel build options?) the Fedora 18
   guest can't display character mode consoles on stdvga, but works well
   with Cirrus. (F18/Xorg/{stdvga,cirrus} are OK, and so are
   RHEL6/{Xorg,console}/{stdvga,cirrus}.)
 Tested with RHEL-6, Fedora 18, and Windows 8 Consumer Preview.

vgasrc/clext.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/vgasrc/clext.c b/vgasrc/clext.c
index dd45df3..d02b880 100644
--- a/vgasrc/clext.c
+++ b/vgasrc/clext.c
@@ -433,6 +433,7 @@ cirrus_switch_mode(struct cirrus_mode_s *table)
     else if (memmodel != MM_TEXT)
         on = 0x01;
     stdvga_attr_mask(0x10, 0x01, on);
+    stdvga_attrindex_write(0x20);
 }

static void