Re: SMRAM sizes on large hosts

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > The problem with this is that I need the TSEG size in another module as
> > well, namely PlatformPei. The dispatch order between PlatformPei and
> > SmmAccessPei is unspecified (they have both TRUE for DEPEX). If
> > PlatformPei gets dispatched second, I really wouldn't want to write to
> > MCH_ESMRAMC again, just to query MCH_TSEGMB. (I couldn't just read
> > MCH_TSEGMB because if PlatformPei were dispatched first, then MCH_TSEGMB
> > would still be unset).
> > 
> > In other words, I wouldn't like to write a register just to receive the
> > information; I need the information in two places whose relative
> > ordering is unspecified, and one of those already writes the register in
> > question, genuinely. I guess I could hack it around with another dynamic
> > PCD, but that's kind of ugly.

Hmm, this unspecified ordering works nicely today because tseg size is a
compile time constant.  If we make this dynamic we either need a pcd or
must probe tseg size twice (no matter whenever this is some pci cfg
space register or fw_cfg file), which is kind of ugly too ...

> > If we invented a read-only, side-effect-free PCI config space register
> > that gave me this value plain and simple (similarly to how a new fw_cfg
> > file would do), that would be a lot cleaner for me.

That makes the "probe twice" thing easier indeed.

> > I think this would
> > match your earlier alternative where you wrote "Alternatively we could
> > add some qemu-specific register".

Yes.

cheers,
  Gerd