Re: [PATCH drm-misc-next v7 4/7] drm/gpuvm: add an abstraction for a VM / BO combination

[Danilo Krummrich]

On 10/31/23 12:25, Thomas Hellström wrote:
> On Mon, 2023-10-23 at 22:16 +0200, Danilo Krummrich wrote:
> > Add an abstraction layer between the drm_gpuva mappings of a
> > particular
> > drm_gem_object and this GEM object itself. The abstraction represents
> > a
> > combination of a drm_gem_object and drm_gpuvm. The drm_gem_object
> > holds
> > a list of drm_gpuvm_bo structures (the structure representing this
> > abstraction), while each drm_gpuvm_bo contains list of mappings of
> > this
> > GEM object.
> >
> > This has multiple advantages:
> >
> > 1) We can use the drm_gpuvm_bo structure to attach it to various
> > lists
> >     of the drm_gpuvm. This is useful for tracking external and evicted
> >     objects per VM, which is introduced in subsequent patches.
> >
> > 2) Finding mappings of a certain drm_gem_object mapped in a certain
> >     drm_gpuvm becomes much cheaper.
> >
> > 3) Drivers can derive and extend the structure to easily represent
> >     driver specific states of a BO for a certain GPUVM.
> >
> > The idea of this abstraction was taken from amdgpu, hence the credit
> > for
> > this idea goes to the developers of amdgpu.
> >
> > Cc: Christian König <christian.koenig@xxxxxxx>
> > Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_gpuvm.c            | 335 +++++++++++++++++++++--
> > --
> >   drivers/gpu/drm/nouveau/nouveau_uvmm.c |  64 +++--
> >   include/drm/drm_gem.h                  |  32 +--
> >   include/drm/drm_gpuvm.h                | 188 +++++++++++++-
> >   4 files changed, 533 insertions(+), 86 deletions(-)
>
> That checkpatch.pl error still remains as well.

I guess you refer to:

ERROR: do not use assignment in if condition
#633: FILE: drivers/gpu/drm/nouveau/nouveau_uvmm.c:1165:
+                       if (!(op->gem.obj = obj))

This was an intentional decision, since in this specific case it seems to
be more readable than the alternatives.

However, if we consider this to be a hard rule, which we never ever break,
I'm fine changing it too.

> Thanks,
> Thomas