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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Fri, 09 May 2014 13:54:39 +0200
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Subject: Re: [Qemu-devel] [PATCH] cirrus_vga: adding sanity check for vram
 size
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To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: weidong.huang@huawei.com, mst@redhat.com, qemu-devel@nongnu.org, arei.gonglei@huawei.com, pbonzini@redhat.com, afaerber@suse.de

  Hi,

> virt-manager/libvirt seems to default to 9 MByte of Vram for cirrus,
> so this would break a lot of setups.

It wouldn't.  libvirt sticks that into the xml, but it doesn't set any
qemu parameters.  The libvirt parameter actually predates the qemu
property for setting the size.

> Looking at datasheets on the web seems to say the chips actually went
> down to 1 MB or less.

I have my doubts we emulate that correctly (register telling the guest
how much memory is actually there etc.).  Also it is pretty much useless
these days, even the 4MB imply serious constrains when FullHD displays
are commonplace.  Newer cirrus drivers such as the kernel's drm driver
are specifically written to qemu's cirrus cards, I have my doubs that
they are prepared to handle 1MB cirrus cards correctly.

Bottom line: Allowing less than 4MB is asking for trouble for no good
reason ;)

cheers,
  Gerd