[SeaBIOS] [PATCH v3] config: allow DEBUG_IO for !QEMU

[Kevin O'Connor]

On Fri, May 31, 2013 at 03:30:48PM +0200, Laszlo Ersek wrote:
> On 05/31/13 03:09, Kevin O'Connor wrote:
> > Same problem - one can't reliably do an inb(0xe9) on real hardware
> > without risking mysterious failures.
> 
> This entire problem seems to exist only if someone runs a SeaBIOS binary
> on real hardware that was configured like:
> - COREBOOT or CSM (ie. not QEMU),
> - and QEMU_HARDWARE.
> 
> Why would someone set QEMU_HARDWARE ("Support hardware found on
> emulators") for a binary intended to run on real hardware?

It's common to build seabios with all options enabled and let seabios
auto-detect what it can use.  That's the intent of QEMU_HARDWARE - it
allows one to compile in more drivers and seabios will use them if it
detects the corresponding hardware.  This does not obviate the need
for proper hardware detection though.

If this goes wrong on real hardware, it could require a lengthy
session with a soldering iron to fix it.  People don't like that.

[...]
> What if we replace the inb() in the proposed patch with a cpuid call
> that detects only KVM, as first step? On KVM it would do the right
> thing, on bare metal, ditto. On other hypervisors it would err towards
> safety and could be extended later. What do you think?

The plan was to detect qemu on coreboot via the mainboard vendor/part
info that coreboot generates.  The plan on uefi was to use the smbios
tables to detect qemu.  Once detection is in place, the DEBUG_IO
support could be made dependent on QEMU_HARDWARE and only activated
after detection succeeds.

-Kevin