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

From: Dr. David Alan Gilbert
Subject: Re: [Qemu-devel] [PATCH] cirrus_vga: adding sanity check for vram size
Date: Fri, 9 May 2014 13:02:25 +0100
User-agent: Mutt/1.5.23 (2014-03-12)

* Gerd Hoffmann (address@hidden) 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.

Yeuch messy.

> > 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 ;)

OK, so checking for 4MB/8MB/16MB is probably safe, and it also would
have the benefit of shouting if someone fixed libvirt and it started
trying to configure a 9MB version.

Dr. David Alan Gilbert / address@hidden / Manchester, UK

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