If I disable coreboot framebuffer support in SeaBIOS and then use the
VGABIOS from the stock ROM in RW_LEGACY, I don't get any display from
SeaBIOS on Broadwell.
If I do the same with a Haswell Chromebook, the display works.
In the former case, SeaBIOS appears to find and load the VGABIOS,
according
to cbmem, just no display.
I think whatever this problem is may also explain why I'm not able to
get
display using a modified BOOT_STUB with SeaBIOS on Broadwell.
IIUC, the intel vgabios fails to work properly on some gpus if it is
run after the hardware has already been initialized. If that's the
case you'd need to be careful to only init the display once (either
native coreboot vga + SeaVGABIOS cbvga, or no video in coreboot +
SeaBIOS run intel vgabios).
Yes, which is why I removed the intel vgabios from the coreboot part of
the ROM, to make sure coreboot wasn't able to initialise it to begin
with. The backlight comes on, but I don't get any display until the
kernel loads.
Another thing that may or may not have some bearing is that on
Baytrail, if
I try to use RW_LEGACY with SeaBIOS, SeaBIOS initialises the display,
but
Linux won't display anything unless I disable KMS with "nomodeset" on
the
kernel cmdline. That unfortunately leaves me with a display resolution
of
1024x768 (presumably what coreboot sets the framebuffer to).
When you say "SeaBIOS initialises the display" do you mean cbvga
SeaVGABIOS? If so, that does not initialize the hardware - it just
draws on the framebuffer that coreboot sets up. I'm not sure why
Linux wouldn't be able to use a display that coreboot setup. Maybe
there is some setting that will convince it to use it.
When I say initialise in that case, I mean "give some display". ;)
Yes, well, as I said, it will bring up a display if I use "nomodeset"
but it's only 1024x768 (not 1366x768), and it won't allow me to change
the resolution in Gnome.
If you have some stuff I can try to get a VGABIOS working properly
with
BOOT_STUB and RW_LEGACY on Broadwell and Baytrail Chromebooks, I would
sure
appreciate it, Kevin.
[...]
>P.S. it should be possible to implement a SeaVGABIOS with support for
>mode switching on Intel graphics adapters. That should solve these
>problems (at least on Intel hardware), but it's a bit of work as I
>find the Intel graphics manuals to be basically indecipherable. :-(
I don't have anything. A few months ago I looked through the Intel
gpu docs. As near as I can tell, the Intel hardware is compatible
with all the legacy VGA interfaces. It seemed like the only thing
that would need to be done to switch into true legacy modes would be
to enable the "legacy vga mode" and to program something called a
"panel fitter". The docs were not much help though.
Well, Matt DeVillier has some experience tweaking the Intel vgabios to
do things like output to the HDMI port first, maybe there're some things
I can experiment with in that area. I'll have a look anyway.
-John.
_______________________________________________
SeaBIOS mailing list
SeaBIOS@seabios.org
http://www.seabios.org/mailman/listinfo/seabios
