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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Gerd Hoffmann (kraxel@redhat.com) 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.

Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK