Re: [PATCH] tools: Remove support for qemu-trad's battery reporting

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Tue, Mar 25, 2025 at 05:41:10PM +0000, Alejandro Vallejo wrote:
> The way this undocumented feature works is via qemu-trad (who nobody
> uses anymore), by intercepting 3 magic PIOs. 0x88 is one of them, and
> it's probed by hvmloader as a means of detecting support for this (so,
> on qemu-upstream this check always fails). If hvmloader detects the
> feature, it appends an SSDT with AML inherited from some laptop ~20y
> ago. QEMU then communicates with a userspace daemon (xenpmd) via an
> undocumented xenstore key ("refreshbatterystatus") in order to report
> battery levels.
> 
> Seeing how no one uses, mantains or cares about qemu-trad anymore, rip
> it all out. The hvmloader check, the SSDT generation logic and xenpmd.

Oh, I didn't know something like this existed!
We needed a feature like this, and solved it via extra kernel module +
PV-like interface to feed it with data from dom0:
https://github.com/QubesOS/qubes-dummy-psu/

I guess it doesn't make much sense for me to resurrect the old interface
and bring it to QEMU upstream, as I need the battery info in PVH too.
So, I'm fine with removing it as is.

> Signed-off-by: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
> ---
> If this feature is truly wanted, it must be implemented in
> qemu-upstream. Ideally in a MUCH less roundabout way. And definitely
> without involving xenstore.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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