[OpenBIOS] HelenOS regression in QEMU implies OpenBIOS VGA issue
benh at kernel.crashing.org
Fri Mar 16 21:59:18 CET 2012
On Fri, 2012-03-16 at 16:44 +0000, Mark Cave-Ayland wrote:
> Hi all,
> Whilst looking at Jakub's bug report here
> https://bugs.launchpad.net/qemu/+bug/942299, I've been working on a
> patch to correct the QEMU interrupt handler on qemu-ppc. Now that this
> bug is close to being fixed, I've had a look at OpenBIOS to find out why
> newer versions of OpenBIOS freeze before the HelenOS loading screen.
I observed that as well, it hangs some time during the display of
the boot messages.
> A local git bisect shows that the culprit is actually this commit:
> commit b6de01a59394f1fafbfb2c65cb784c9d23067fa2
> Author: laurent <laurent at f158a5a8-5612-0410-a976-696ce0be7e32>
> Date: Tue Aug 4 21:08:37 2009 +0000
> Allows to configure screen size from Qemu command line options
> using FW_CFG
> Only enabled for PPC/QEMU and VGA/VBE.
I'm surprised by that. This has worked well for a long time, I think
something else in qemu causes that commit to fail.
> git-svn-id: svn://openbios.org/openbios/trunk@538
> Having stepped through vga_vbe_init() in drivers/vga_vbe.c, the only
> difference is that reading the display depth from the QEMU FW CFG
> interface returns 15 instead of the in-built OpenBIOS default of 8.
AFAIK that's been working fine for a while...
> So is a bit-depth of 15 supported by OpenBIOS? This seems quite unusual
> given that it is not a power of 2; however if I use GDB to override the
> value to 16 then HelenOS boots but with a blue screen BIOS on VGA so I'm
> not sure that is the correct solution either. Does anyone know what the
> default bit-depth is in Apple's firmware?
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