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Re: [Qemu-devel] vga-pci and MMIO BAR

From: Benjamin Herrenschmidt
Subject: Re: [Qemu-devel] vga-pci and MMIO BAR
Date: Wed, 25 Jul 2012 20:53:38 +1000

On Wed, 2012-07-25 at 13:27 +0300, Avi Kivity wrote:
> On 07/25/2012 06:57 AM, Benjamin Herrenschmidt wrote:
> > Hi folks !
> > 
> > Would there be any objection to adding a second MMIO BAR to qemu-vga
> > which mirrors the bochs magic VBE ports ?
> > 
> > Support for IO space is optional in PCIe and can be problematic on some
> > architectures, it would be nice to be able to program the card entirely
> > using mmio.
> Can we choose a PCIe chipset that does support IO space?

Why bother ? It's not like mode setting is performance critical and IO
space is always going to be a pain on non-x86 ...

> If not, we can add a second BAR, but it should disappear when running an
> older machine type.

Well, the IO ports in legacy space are still there. We can also make the
"register BAR" exist in both mode or we can add a second BAR and have
x86 "prefer" IO... whatever rocks your boat as long as it's a BAR, it's
the legacy hole that's annoying for me :-)

> > Once done, I'd like to look into doing a qemudrmfb similar to the cirrus
> > one that pretty much gives you generic KMS support (with RandR) on top
> > of vga-pci. This would have the advantage of potentially lifting the
> > pitch and size limitations that plague cirrus.
> Have a look at qxl.

No I haven't :-) I'll have a look, thanks.


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