[RFC PATCH 1/2] drm/hyperv: Add DRM driver for hyperv synthetic video device

[Gerd Hoffmann]

  Hi,

> > > > +	msg->vram.user_ctx = msg->vram.vram_gpa = vram_pp;
> > > > +	msg->vram.is_vram_gpa_specified = 1;
> > > > +	synthvid_send(hdev, msg);
> > > 
> > > That suggests it is possible to define multiple framebuffers in vram,
> > > then pageflip by setting vram.vram_gpa.  If that is the case I'm
> > > wondering whenever vram helpers are a better fit maybe?  You don't
> > > have
> > > to blit each and every display update then.
> > 
> > Thanks for the review. Unfortunately only the first vmbus message take
> > effect and subsequent calls are ignored. I originally implemented using
> > vram helpers but I figured out calling this vmbus message again won't
> > change the vram location.

/me notices there also is user_ctx.  What is this?

> I think that needs a very big comment. Maybe even enforce that with a
> "vram_gpa_set" boolean in the device structure, and complain if we try to
> do that twice.
> 
> Also I guess congrats to microsoft for defining things like that :-/

I would be kind of surprised if the virtual device doesn't support
pageflips.  Maybe setting vram_gpa just isn't the correct way to do
it.  Is there a specification available?

There are a number of microsoft folks in Cc:  Anyone willing to comment?

thanks,
  Gerd

PS: And, yes, in case pageflips really don't work going with shmem
    helpers + blits is reasonable.