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Subject: Re: [Qemu-devel] [PATCH] hda-codec: use smaller dynamic range for
 input amplifier
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To: =?ISO-8859-1?Q?Marc-Andr=E9?= Lureau <mlureau@redhat.com>
Cc: Martin Wilck <martin.wilck@ts.fujitsu.com>, qemu-devel@nongnu.org

  Hi,

> > The "right" solution for this problem would be to implement
> > proper dB scaling in QEMU and the audio backends (such as spice).

Can we try this please?

> > While this clean solution is not available, I suggest to decrease
> > the dynamic range for the the emulated Amps in the QEMU hda codec.
> > Experiments showed that with 32dB dynamic range with a 0.5 dB step,
> > it was possible to set gain values as low as 5 (-29.5dB / 8%).
> > Actual HW seems to use similar ranges for input amplifiers.

> I am afraid guest OS won't like it the card description changes after a migration.
> This will likely need a new VMState field, for the steps, or the amp caps.

Correct.  This is a guest-visible change, so we have to make this
runtime-switchable for compatibility with older qemu versions.  This
quickly becomes a bit messy, so I'd prefer to avoid this.

cheers,
  Gerd