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

[Gabriel L. Somlo]

On Tue, Sep 01, 2015 at 09:10:23PM +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".
> (For ARM we don't I think currently expose fw_cfg in the ACPI
> tables, but we probably ought to; only needed for the edge
> case where you actually wanted to read fw_cfg in the guest
> kernel rather than just the guest firmware, though.)

Right, that's what I'm trying to do -- expose fw_cfg in
/sys/firmware/... on the guest -- which involves figuring out how
to determine if it is present (DT on ARM, blindly poking port 0x510
on x86 for now, hence my interest in having it listed in ACPI).

Now, if we did expose fw_cfg in ACPI on *both* ARM and x86, I wonder
I could get away with an ACPI-only detection scheme across both
architectures... But ACPI is all we have on x86, so on the QEMU side
of things it looks like I'll have to add it regardless...

Thanks,
--Gabriel