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Re: [Qemu-devel] [PATCH] cirrus_vga: adding sanity check for vram size

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH] cirrus_vga: adding sanity check for vram size
Date: Mon, 12 May 2014 11:05:24 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

[adding libvirt]

On 05/09/2014 05:54 AM, Gerd Hoffmann wrote:
>   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.

Then we should probably re-evaluate what libvirt does with the
parameters, which avoids breaking any guest that happens to be
pre-existing with the odd 9MB sizing in the XML.

>> 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

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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