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

[Danilo Krummrich <dakr@redhat.com>]

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@amd.com>
>> Signed-off-by: Danilo Krummrich <dakr@redhat.com>
>> ---
>>   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
>