[Nouveau] Trouble with TTM patches w/nouveau in linux-next

[Ilia Mirkin]

GEM init happens here:

https://cgit.freedesktop.org/drm/drm/tree/drivers/gpu/drm/nouveau/nouveau_gem.c#n221

Note the bo alloc / gem init / bo init dance.

I don't think there is a GEM object for internal allocations at all --
we just allocate bo's directly and that's it. Perhaps you meant
something else? I thought GEM was meant for externally-available
objects.

Cheers,

  -ilia

On Wed, Jun 9, 2021 at 10:58 AM Christian König
<christian.koenig at amd.com> wrote:
>
> Good point, but I think that is unrelated.
>
> My suspicion is rather that nouveau is not initializing the underlying
> GEM object for internal allocations.
>
> So what happens is the same as on VMWGFX that TTM doesn't know anything
> about the size to of the BO resulting in a kmalloc() with a random value
> and eventually -ENOMEM.
>
> Good news is that I can reproduce it, so going to look into that later
> today.
>
> Regards,
> Christian.
>
> Am 09.06.21 um 16:52 schrieb Ilia Mirkin:
> > Christian - potentially relevant is that Tegra doesn't have VRAM at
> > all -- all GTT (or GART or whatever it's called nowadays). No
> > fake/stolen VRAM.
> >
> > Cheers,
> >
> >    -ilia
> >
> > On Wed, Jun 9, 2021 at 10:18 AM Christian König
> > <christian.koenig at amd.com> wrote:
> >> Hi Mikko,
> >>
> >> strange sounds like Nouveau was somehow also using the GEM workaround
> >> for VMWGFX as well.
> >>
> >> But -12 means -ENOMEM which doesn't fits into the picture.
> >>
> >> I will try with a G710, but if that doesn't yields anything I need some
> >> more input from you.
> >>
> >> Thanks for the report,
> >> Christian.
> >>
> >>
> >> Am 09.06.21 um 15:47 schrieb Mikko Perttunen:
> >>> Hi,
> >>>
> >>> I'm observing nouveau not initializing recently on linux-next on my
> >>> Tegra186 Jetson TX2 board. Specifically it looks like BO allocation is
> >>> failing when initializing the sync subsystem:
> >>>
> >>> [   21.858149] nouveau 17000000.gpu: DRM: failed to initialise sync
> >>> subsystem, -28
> >>>
> >>> I have been bisecting and I have found two patches that affect this.
> >>> Firstly, things first break on
> >>>
> >>> d02117f8efaa drm/ttm: remove special handling for non GEM drivers
> >>>
> >>> starting to return error code -12. Then, at
> >>>
> >>> d79025c7f5e3 drm/ttm: always initialize the full ttm_resource v2
> >>>
> >>> the error code changes to the above -28.
> >>>
> >>> If I checkout one commit prior to d79025c7f5e3 and revert
> >>> d02117f8efaa, things work again. There are a bunch of other TTM
> >>> commits between this and HEAD, so reverting these on top of HEAD
> >>> doesn't work. However, I checked that both yesterday's and today's
> >>> nexts are also broken.
> >>>
> >>> Thank you,
> >>> Mikko
> >>>
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