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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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.

(Am I alone in thinking that "thru" is a horrible alternative to
through?)

>  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"?

> +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.

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
(or better yet somebody could finally submit the patches for inclusion).

> +gfx_passthru is currently only supported with the qemu-xen-traditional
> +device-model. Upstream qemu-xen device-model currently doesn't have
> +support for gfx_passthru.
> +
> +Note that some graphics adapters (AMD/ATI cards, for example) don't
> +necessarily require gfx_passthru option, so you can use the normal
> +Xen PCI passthru to assign the graphics card as a secondary graphics card
> +to the VM. Qemu emulated graphics card stays as the primary graphics card, 
> +and you get VNC output from the Qemu-emulated primary adapter.
> +
>  
>  =item B<nomigrate=BOOLEAN>
> 



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