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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Tue, 02 Feb 2016 15:23:32 +0100
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Subject: Re: [Qemu-devel] [PATCH v4] Add optionrom compatible with fw_cfg
	DMA version
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To: Marc =?ISO-8859-1?Q?Mar=ED?= <marc.mari.barcelo@gmail.com>
Cc: "Gabriel L. Somlo" <somlo@cmu.edu>, qemu-devel@nongnu.org, Kevin O'Connor <kevin@koconnor.net>, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Marc =?ISO-8859-1?Q?Mar=ED?= <markmb@redhat.com>, Laszlo <lersek@redhat.com>

  Hi,

> I don't remember discussing the topic of machine types when touching
> fw_cfg DMA. Which means, it probably slipped amongst the other details.
> But it is now merged and in stable, so it should probably be left as it
> is now.

We have to fix it, it breaks live migration.  With fw_cfg_dma turned on
we send an extra vmstate section.  qemu 2.4 (+older) will not understand
it.  So we have to turn it off for those machine types.

dma_enabled property is there already, but the logic is wrong.  It
defaults to false, but is flipped to true when the arch supports dma
(i.e. on x86 and arm), unconditionally.  Instead it should default to
true.  When set to false by the user or compat properties don't enable
fw_cfg dma (and also flip it to false when dma is not supported by the
arch).

> Should this optionrom be enabled only with the latest machine type?

The logic to pick the correct rom is fine.

cheers,
  Gerd