[coreboot] Question about Intel HD graphics and FLR

Nico Huber nico.h at gmx.de
Thu Mar 30 20:36:44 CEST 2017

Hi JP,

On 30.03.2017 17:48, Joshua Pincus wrote:
> Hi Zoran,
> Thanks for your reply.
> My situation is this: When the VM guest comes up the first time from a
> system-level reset (aka power on), the Broadwell HD graphics device runs
> fine.  I see basic VGA both before and during the boot of Windows.  Once
> Windows boots, the HD graphics device is configured by Intel's driver and I
> see hi-rez output.  On a reboot of Windows within the VM, an FLR is
> issued.  When the guest comes back up, no VGA.  Windows does boot but
> provides no VGA output.  If Windows needs to drop into VGA mode so that a
> user can access the real-mode functionality of the recovery console, still
> no VGA.

what kind of VM? what does it usually do when booting to support windows
(supposedly runs some BIOS / UEFI code)? Does that include running a
VBIOS or GOP UEFI driver?

> It's only on Broadwell-based boards that we have this problem.  If we issue
> FLRs during the reset of the PCI bus for older Intel boards, no problem.
> We get VGA.  Something involved with the FLR is messing up the state of the
> hardware instead of actually returning the hardware to a virgin state, akin
> to what you would get from a full system reset.

AFAIK, Windows doesn't need a virgin state but the state the VBIOS / GOP
driver usually leaves the hardware in. Plus a Video BIOS Table (VBT)
with some hints about a board's specifics. What are these older boards?
Are you sure they support FLR? The first hints about FLR support I could
find were is a Haswell datasheet.


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