Re: [Qemu-devel] [PATCH v2 1/5] fw_cfg: document fw_cfg_modify_iXX() update functions

[Gerd Hoffmann]

On Di, 2015-09-01 at 21:10 +0100, Peter Maydell wrote:
> On 1 September 2015 at 20:13, Gabriel L. Somlo <address@hidden> wrote:
> > Also, since I'll be tinkering with fw_cfg again, and you mentioned
> > using DT on arm and ACPI on x86 to auto-detect the presence (and location)
> > of fw_cfg from the guest-side in a related thread:
> 
> I meant DT or ACPI on ARM, actually. I don't know what the x86
> approach is for fw_cfg but I think it's just "known address".

Yes, "known address".  And given that the firmware actually loads the
acpi tables via fw_cfg that is very unlikely to change.  Adding it to
the acpi tables might be useful nevertheless so the guest os knows the
ioports are in use.

I think on arm the acpi situation is the same, but I think firmware
detecting the location via DT should work without chicken&egg problems.

cheers,
  Gerd