Re: [PATCH] OvmfPkg: initialize bochs when initializing vmsvga

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> Please help me see the situation better. Here's my current
> understanding.
> 
> (1) QemuVideoDxe doesn't set up the VMW SVGA FIFO, and does not store 1
>     to the SVGA_REG_CONFIG_DONE register. And this is not a "small
>     missing step" -- the FIFO setup can be considered a separate
>     feature.
> 
> (2) We don't intend to implement the FIFO setup feature. (In particular
>     because we don't intend to track changed rectangles and send updates
>     via the FIFO.)
> 
> (3) The intent of the original VMW SVGA enablement patch for
>     QemuVideoDxe, namely commit c137d9508169, was to enable booting some
>     UEFI operating systems on OVMF that had guest drivers only for VMW
>     SVGA.
> 
> (4) The QEMU device model now -- since commit 104bd1dc70 -- falls back
>     to stdvga (that is, Bochs) in response to QemuVideoDxe's actions.
> 
> (5) Your proposal is to set up the Bochs interface in QemuVideoDxe, *in
>     addition* to the -- now dysfunctional! -- VMW SVGA interface.
> 
> Is my understanding correct?

I understand things the same way.

> So, what do you think of the following approach, instead of your
> currently proposed patch:
> 
> - revert commit c137d9508169 ("OvmfPkg/QemuVideoDxe: VMWare SVGA device
>   support", 2017-04-07)
> 
> - revert commit 05a537945872 ("OvmfPkg/QemuVideoDxe: Helper functions
>   for unaligned port I/O.", 2017-04-07)
> 
> - given that QEMU provides the Bochs interface anyway, with the VMW SVGA
>   device model, simply recognize the "QEMU VMWare SVGA" card, in the
>   "gQemuVideoCardList" array, as the QEMU_VIDEO_BOCHS_MMIO variant.

Makes sense to me.

Alternatively write a full-blown vmsvga driver which works simliar to
the virtio-gpu driver.  I have my doubts this is worth the effort
though.

> Before QEMU commit 104bd1dc70, was it really *required* to use the (now
> dead) QemuVideoDxe code for VMW SVGA, or would it always have been
> possible to simply use the Bochs interface, to drive the VMW SVGA
> device?

I think bochs interface works works with all vmsvga version (in qemu).
Didn't test though.

cheers,
  Gerd