Re: [Qemu-devel] [PATCH v13 0/8] pv event interface between host and guest

[Paolo Bonzini]

Il 04/03/2013 11:21, Gleb Natapov ha scritto:
>> > Just to clarify it for Hu Tao, the read from a random ioport is how the
>> > ACPI code will detect presence of the device.
>> > 
> Actually no (at least in the long run, for the first version it may be
> OK).

Agreed.

> Since we want to move DSDT generation into QEMU if device will not
> be present QEMU will not generate corresponded Device() in DSDT, or it
> will generate it with _STA() { Return (0x00)} hard coded.

Yes, this would be good.

> Seabios can do
> the same if we will pass it info about device presence via fw_cfg.

True, but I don't like this a lot.  I don't like splitting decisions
between SeaBIOS and the DSDT, you end up touching code all over the
place and writing ASL is simpler than patching---even with all the
machinery that we have.  It is also simpler to move ASL from SeaBIOS to
OVMF and/or viceversa.  I don't recall what was the opposition to a
fw_cfg driver directly in the DSDT, but I think this would be a good
usage for it.

Splitting it between QEMU and DSDT is a bit better, since you have to
touch QEMU anyway to implement the feature.

Anyhow, this does not apply to the next submission of this series.  I
think we can agree to the compromise of using ACPI but still read the
port in _STA.

Paolo