Re: [Qemu-devel] [Intel-gfx] [Announcement] 2015-Q3 release of XenGT - a Mediated Graphics Passthrough Solution from Intel

[Zhiyuan Lv]

On Fri, Nov 20, 2015 at 04:36:15PM +0800, Tian, Kevin wrote:
> > From: Gerd Hoffmann [mailto:address@hidden
> > Sent: Friday, November 20, 2015 4:26 PM
> > 
> >   Hi,
> > 
> > > > iGVT-g_Setup_Guide.txt mentions a "Indirect Display Mode", but doesn't
> > > > explain how the guest framebuffer can be accessed then.
> > >
> > > You can check "fb_decoder.h". One thing to clarify. Its format is
> > > actually based on drm definition, instead of OpenGL. Sorry for
> > > that.
> > 
> > drm is fine.  That header explains the format, but not how it can be
> > accessed.  Is the guest fb exported as dma-buf?
> 
> Currently not, but per our previous discussion we should move to use
> dma-buf. We have some demo code in user space. Not sure whether
> they're public now. Jike could you help do a check?

Our current implementation did not use dma-buf yet, still based on DRM_FLINK
interface. We will switch to dma-buf. Thanks!

Regards,
-Zhiyuan

> 
> > 
> > > > So, for non-opengl rendering qemu needs the guest framebuffer data so it
> > > > can feed it into the vnc server.  The vfio framebuffer region is meant
> > > > to support this use case.
> > >
> > > what's the format requirement on that framebuffer? If you are familiar
> > > with Intel Graphics, there's a so-called tiling feature applied on frame
> > > buffer so it can't be used as a raw input to vnc server. w/o opengl you
> > > need do some conversion on CPU first.
> > 
> > Yes, that conversion needs to happen, qemu can't deal with tiled
> > graphics.  Anything which pixman can handle will work.  Prefered would
> > be PIXMAN_x8r8g8b8 (aka DRM_FORMAT_XRGB8888 on little endian host) which
> > is the format used by the vnc server (and other places in qemu)
> > internally.
> > 
> > qemu can also use the opengl texture for the guest fb, then fetch the
> > data with glReadPixels().  Which will probably do exactly the same
> > conversion.  But it'll add a opengl dependency to the non-opengl
> > rendering path in qemu, would be nice if we can avoid that.
> > 
> > While being at it:  When importing a dma-buf with a tiled framebuffer
> > into opengl (via eglCreateImageKHR + EGL_LINUX_DMA_BUF_EXT) I suspect we
> > have to pass in the tile size as attribute to make it work.  Is that
> > correct?
> > 
> 
> I'd guess so, but need double confirm later when reaching that level of 
> detail. 
> some homework on dma-buf is required first. :-)
> 
> Thanks
> Kevin