Re: [Xen-devel] [PATCH] xl.cfg: gfx_passthru documentation improvements

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-09-04 at 20:12 +0100, Pasi KÃrkkÃinen wrote:
> On Mon, Sep 03, 2012 at 11:10:53AM +0100, Ian Campbell wrote:
> > On Sun, 2012-09-02 at 06:35 +0100, Pasi KÃrkkÃinen wrote:
> > > Hello,
> > > 
> > > xl.cfg.pod.5 documentation improvements:
> > > 
> > > - gfx_passthru: Document gfx_passthru makes the GPU become primary in the 
> > > guest
> > >   and other generic info about gfx_passthru.
> > > 
> > > 
> > > Signed-off-by: Pasi KÃrkkÃinen <pasik@xxxxxx>
> > > --- docs/man/xl.cfg.pod.5.orig1 2012-09-02 07:16:39.316782158 +0300
> > > +++ docs/man/xl.cfg.pod.5       2012-09-02 08:26:40.081639087 +0300
> > > @@ -968,7 +968,43 @@
> > >  
> > >  =item B<gfx_passthru=BOOLEAN>
> > >  
> > > -Enable graphics device PCI passthrough. XXX which device is passed 
> > > through ?
> > > +Enable graphics device PCI passthrough. This option makes the passthru
> > > +graphics card become primary graphics card in the VM,
> > 
> > The option is slightly misnamed then I guess, a better name would have
> > been gfx_passthru_primary? oh well, we are stuck with it now.
> > 
> 
> Yeah.. I think earlier gfx_passthru wasn't a boolean, but an integer, to 
> choose the mode.

Oh, do you happen to know what the meanings were?

> > >  so the Qemu emulated 
> > > +graphics adapter is disabled, and the VNC console for the VM won't have
> > > +any graphics output. All graphics output, including boot time Qemu BIOS
> > > +messages from the VM, will go to the physical outputs of the passed thru
> > > +physical graphics card.
> > > +
> > > +Graphics card PCI device to passthru is chosen with B<pci> option, 
> > > +exactly in the same way as normal Xen PCI device passthru/assignment is 
> > > done. 
> > > +Note that gfx_passthru doesn't do any kind of sharing
> > > +of the GPU, so you can only assign the GPU to one single VM at a time.
> > > +
> > > +gfx_passthru also enables various legacy VGA memory ranges, BARs, MMIOs, 
> > > +and ioports to be passed thru to the VM, since those are required
> > > +for correct operation of things like VGA BIOS, text mode, VBE, etc.
> > > +
> > > +Enabling gfx_passthru option also copies the physical graphics card 
> > > +video bios to the guest memory, and executes the vbios in the guest 
> > 
> > "BIOS" and (I expect) "VBIOS"?
> > 
> 
> video bios == vbios, or did you ask something else? 

I was just commenting on the capitalisation differing from other
mentions of the BIOS.

> > > +to get the graphics card initialized.
> > > +
> > > +Most graphics adapters require vendor specific tweaks for properly
> > > +working graphics passthru. Xen currently includes necessary tweaks
> > > +for Intel IGD (Integrated Graphics Device) GPUs.  
> > > +
> > > +Support for AMD/Nvidia gfx_passthru is not yet merged to Xen,
> > > +but there are out-of-tree patches available.
> > 
> > If there is a comprehensive list of supported/not-supported devices on
> > the wiki then I think a reference here would be more useful than these
> > two brief paragraphs.
> > 
> 
> We have a list, but it's not up-to-date unfortunately:
> http://wiki.xen.org/wiki/XenVGAPassthroughTestedAdapters

I think it is worth referencing it, and perhaps adding a note to the
page itself regarding its freshness (and then working to improve it, of
course ;-))

> > In particular the second isn't very useful without links and those tend
> > to become out of date in docs IME, I would tend to omit this from here
> > and instead include them in the wiki where they can be kept up to date
> >
> 
> Ok. I'll fix that, and add a link to:
> http://wiki.xen.org/wiki/XenVGAPassthrough

Thanks.

Ian.


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