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 <kra...@redhat.com> cheers, Gerd
