linux-kernel - Re: [virtio-dev] Re: [PATCH] Add virtio gpu driver.

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Date:	Thu, 26 Mar 2015 16:07:16 +0100
From:	Gerd Hoffmann <kraxel@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	virtio-dev@...ts.oasis-open.org, Dave Airlie <airlied@...il.com>,
	Dave Airlie <airlied@...hat.com>,
	David Airlie <airlied@...ux.ie>,
	Rusty Russell <rusty@...tcorp.com.au>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
	"open list:VIRTIO CORE, NET..." 
	<virtualization@...ts.linux-foundation.org>,
	"open list:ABI/API" <linux-api@...r.kernel.org>
Subject: Re: [virtio-dev] Re: [PATCH] Add virtio gpu driver.

  Hi,

> I don't know. This seems exactly like the kind of thing
> we had in mind when we added the virtio pci capability.
> For example, we have text in spec that requires drivers
> to skip unknown capabilities.
> 
> And yes, if bios pokes at a specific bar then we do
> need to list this info in the virtio spec so this makes
> it an issue that is virtio related.

Hmm, virtio-vga is a two-in-one device basically.  When virtio is
enabled it behaves like virtio-gpu-pci, otherwise it behaves very
simliar to stdvga.  So you need to know nothing about virtio to handle
the vga side, and I want keep it that way.

When no vga compatibility is needed there always is the option to just
use virtio-gpu-pci instead.

> Yes, it's not about what we put there now. It's about being able
> to move things about in the future without breaking guests.

We don't have that today for stdvga, and I still fail to see what this
buys us.

Completely different thing crossing my mind:  I think we can make
virtio-vga fully compatible with stdvga.  stdvga has two bars, memory
(#0) and mmio (#2).  We can make the mmio bar larger and place all the
virtio regions there.

I think in any case I'll go split off the vga compatibility bits to a
different patch (and possible a separate patch series).

cheers,
  Gerd

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