Re: [PATCH v5 8/8] docs/system: Expand the virtio-gpu documentation

[Akihiko Odaki <akihiko.odaki@daynix.com>]

On 2025/02/06 2:40, Dmitry Osipenko wrote:
> On 2/3/25 08:31, Akihiko Odaki wrote:
> ...
>>> Requirements don't vary much. For example virglrenderer minigbm support
>>> is mandatory for crosvm, while for QEMU it's not.
>>
>> Is that true? It seems that virglrenderer uses builds without minigbm
>> support to run tests on GitLab CI.
> 
> CI is running in a headless mode using software renderer. For a
> full-featured crosvm support running on a baremetal, minigbm should be
> needed, along with other downstream features.

That makes sense.

Based on your input, for QEMU, I don't think we need a separate 
documentation to describe libvirglrenderer's build flags though crosvm 
should have some documentation saying it requires minigbm.

> 
>> Anyway, if there is any variance in the build procedure, that may
>> justify having a separate build instruction in QEMU tree to avoid
>> confusion. Otherwise, it's better to have a documentation shared with
>> other VMMs.
>>
>>>
>>>> I'm not entirely sure the documentation will stay as is for that long.
>>>> The requirements of Intel native context refer to merge requests that
>>>> can be merged sooner or later. Asahi may need more updates if you
>>>> document it too because its DRM ABI is still unstable.
>>>
>>> The unstable parts of course will need to be updated sooner, but the
>>> stable should be solid for years. I expect that about a year later
>>> requirements will need to be revisited.
>>>
>>
>> It will be some burden in the future. Now you are adding this
>> documentation just for QEMU, but crosvm and libkrun may gain similar
>> documentation. The DRM native context support for Intel and Asahi is in
>> development, and I guess nvk will support it someday.
>>
>> So, a very rough estimation of future documentation updates will be:
>> (number of VMMs) * (number of DRM native contexts in development)
>> = 3 * 3
>> = 9
>>
>> That's manageable but suboptimal.
> 
> I don't mind deferring the doc addition if that's preferred. Either way
> is fine with me. Yet it's better to have doc than not.

My suggestion is not to defer the addition, but to add it to Mesa, which 
does not require deferring.

> 
> In my view crosvm and libkrun exist separately from QEMU, they serve a
> different purpose. Majority of QEMU users likely never heard about those
> other VMMs. A unified doc won't be a worthwhile effort, IMO.
> 

When evaluating the utility of a unified documentation, Whether the 
majority of Mesa/Virgl users care VMMs other than QEMU matters more. And 
I think it is true; libkrun and crosvm are excellent options for 
graphics-accelerated VMs.

If we have a unified documentation, any VM can point to it for the build 
instruction of Mesa and virglrenderer. Once that's done, QEMU users who 
want graphics acceleration can take the following steps:
1. See docs/system/devices/virtio-gpu.rst
2. Figure out that they need Mesa and virglrenderer
3. Click the link to the unified documentation
4. Build Mesa and virglrenderer accordingly

No other VMMs will bother them in this procedure.

Regards,
Akihiko Odaki