Re: [Qemu-devel] [PATCH 7/8] virtio-vga: v1

[Dave Airlie <airlied@gmail.com>]

On Thu, Nov 21, 2013 at 9:06 PM, Gerd Hoffmann <kraxel@redhat.com> wrote:
> On Do, 2013-11-21 at 13:12 +1000, Dave Airlie wrote:
>> On Wed, Nov 20, 2013 at 10:02 PM, Gerd Hoffmann <kraxel@redhat.com> wrote:
>> > On Mi, 2013-11-20 at 15:52 +1000, Dave Airlie wrote:
>> >> From: Dave Airlie <airlied@redhat.com>
>> >>
>> >> This is a virtio-vga device built on top of the virtio-gpu device.
>> >
>> > Ah, I see what you use the wrapping for.  Hmm.  I think you should use a
>> > common base class instead, i.e. something like virtio-gpu-base which
>> > holds all the common stuff.  Both virtio-gpu and virtio-vga can use that
>> > as TypeInfo->parent then.  This way virtio-vga doesn't have to muck with
>> > virtio-gpu internals.  virtio-gpu-base can be tagged as abstract class
>> > (using .abstract = true) so it will not be instantiated directly.
>> >
>>
>> I'm not sure what that buys me here, I need the virtio-vga to attach
>> the vga ops the first console that the virtio-gpu registers, it can't
>> be a separate console, and since virtio-gpu initialises before
>> virtio-vga I can't tell it to not register the console.
>
> virtio-gpu-core registers no consoles.  It just export the hw_ops
> functions.   virtio-gpu-core inly initializes the stuff which is
> identical for both virtio-gpu and virtio-vga, everything else is left to
> the init functions of the subclasses.
>
> virtio-gpu uses virtio-gpu-core as parent.  Registers the the consoles,
> using the hw_ops functions exported by virtio-gpu-core.  Also sets the
> pci class to DISPLAY_OTHER.
>
> virtio-vga uses virtio-gpu-core as parent too.  Registers the consoles,
> using functions basically doing "if vgamode then call vga hw_ops else
> call virtio-gpu-core hw_ops".  Simliar to what you have today but
> without the funky wrapping.  Sets pci class to DISPLAY_VGA and
> initializes vga stuff.
>
> cheers,
>   Gerd

Okay I'm really missing something here and I think I've confused
myself completely.

My plan was

virtio-gpu-base - VirtIOGPUBase object - VirtIODevice parent_obj -
abstract class - contains vqs + exposes ops

virtio-gpu - virtio-gpu-base wrapper with init sequence for non-VGA
virtio gpus (mmio + pci)
virtio-gpu-pci - VirtIOPCIProxy parent_obj - contains a VirtIOGPU vdev
that it instantiates in its instance init like all the PCI wrappers

Now the advice given was to have virtio-vga wrap virtio-gpu-base but
from what I can see it really can't. Since it needs to act and look
like a PCI device

virtio-vga: Also has a VirtIOPCIProxy parent_obj, however as
virtio-gpu-base is abstract I can't directly instantiate it, and I
can't instantiate virtio-gpu as its the wrong thing,

so do I really need to add another class? rename virtio-vga to
virtio-pci-vga and add a new virtio-vga that just wraps
virtio-gpu-base?

This is getting a lot messier than the code I had, and the benefits
are escaping me, which must mean I'm misinterpreting the instructions
given.

This then led to another question how do I call the virtio-gpu-base
init functions? directly? as I can't use qdev as they are abstract
from what I can see.

Dave.