Re: [Qemu-devel] [PATCH] q35/mch: implement extended TSEG sizes

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> To be specific, what I meant is a bit that tells guest that a
> config space register is available, and lets host find out
> that guest is going to use it.
> 
> This to ensure full forward and backward compatibility.
> 
> I agree a fw cfg file for a single bit seems like an overkill, that's
> why I thought sharing feature files with SMI would be a good idea.
> 
> Do you see an issue with that?

The point of placing the extended-tseg-size register in mch pci config
is that the firmware can figure this easily *without* looking somewhere
else, as all the other tseg (and smram) config bits are in mch pci
config space too.

When involving fw_cfg there is no reason to keep the extended-tseg-size 
register in mch.  We can simply place a "etc/q35-extended-tseg-size"
file in fw_cfg then (which is either not present or contains the
extended tseg size).  So a feature bit in fw_cfg looks absolutely
pointless to me.

I still think the approach and patch by Laszlo is perfectly fine. 
While being at it:

Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>

cheers,
  Gerd