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

[yuchenlin <yuchenlin@synology.com>]

On 2018-10-23 22:02, Laszlo Ersek wrote:
> On 10/23/18 15:42, Gerd Hoffmann wrote:
>>   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.
> 
> Great, thank you.
> 
>> 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.
> 
> Right, please let us *not* do this.
> 
>> 
>>> 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).
> 
> Great!
> 
>> Didn't test though.
> 
> That's fine; I think I haven't tested VMW SVGA, as in "ever". That's up
> to people that actually use the device model. As I wrote previously,
> it's quite telling that the consequences of QEMU commit 104bd1dc70, 
> from
> release v2.10.0, are reported only now, more than a year after the
> release -- VMW SVGA must not be a very popular device model.
> 
> Yuchenlin, can you then please investigate this approach, including
> testing the reverts (the Bochs-only implementation) against QEMU 
> v2.9.1?
> 

Sure!

Thanks,
yuchenlin

> (FWIW, upstream QEMU doesn't seem to support earlier releases than
> v2.10.2 any longer, according to <https://www.qemu.org/>. So even if 
> the
> v2.9.1 test failed, maybe we shouldn't care, in *upstream* edk2. Still,
> knowing the status would be useful.)
> 
> Thanks!
> Laszlo