linux-kernel - Re: [PATCH v1 1/2] drm/amdgpu: make non-NULL out fence mandatory

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Message-ID: <9e1964bf-7748-4e41-9048-b1a5ad63a8c9@damsy.net>
Date: Tue, 16 Sep 2025 11:46:56 +0200
From: Pierre-Eric Pelloux-Prayer <pierre-eric@...sy.net>
To: Christian König <christian.koenig@....com>,
 Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>,
 Alex Deucher <alexander.deucher@....com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Sumit Semwal <sumit.semwal@...aro.org>
Cc: amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v1 1/2] drm/amdgpu: make non-NULL out fence mandatory



Le 16/09/2025 à 11:25, Christian König a écrit :
> On 16.09.25 09:08, Pierre-Eric Pelloux-Prayer wrote:
>> amdgpu_ttm_copy_mem_to_mem has a single caller, make sure the out
>> fence is non-NULL to simplify the code.
>> Since none of the pointers should be NULL, we can enable
>> __attribute__((nonnull))__.
>>
>> While at it make the function static since it's only used from
>> amdgpuu_ttm.c.
>>
>> Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 17 ++++++++---------
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h |  6 ------
>>   2 files changed, 8 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> index 27ab4e754b2a..70b817b5578d 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> @@ -284,12 +284,13 @@ static int amdgpu_ttm_map_buffer(struct ttm_buffer_object *bo,
>>    * move and different for a BO to BO copy.
>>    *
>>    */
>> -int amdgpu_ttm_copy_mem_to_mem(struct amdgpu_device *adev,
>> -			       const struct amdgpu_copy_mem *src,
>> -			       const struct amdgpu_copy_mem *dst,
>> -			       uint64_t size, bool tmz,
>> -			       struct dma_resv *resv,
>> -			       struct dma_fence **f)
>> +__attribute__((nonnull))
> 
> That looks fishy.
> 
>> +static int amdgpu_ttm_copy_mem_to_mem(struct amdgpu_device *adev,
>> +				      const struct amdgpu_copy_mem *src,
>> +				      const struct amdgpu_copy_mem *dst,
>> +				      uint64_t size, bool tmz,
>> +				      struct dma_resv *resv,
>> +				      struct dma_fence **f)
> 
> I'm not an expert for those, but looking at other examples that should be here and look something like:
> 
> __attribute__((nonnull(7)))

Both syntax are valid. The GCC docs says:

    If no arg-index is given to the nonnull attribute, all pointer arguments are 
marked as non-null


> 
> But I think for this case here it is also not a must have to have that.

I can remove it if you prefer, but it doesn't hurt to have the compiler validate 
usage of the functions.

Pierre-Eric


> 
> Regards,
> Christian.
> 
>>   {
>>   	struct amdgpu_ring *ring = adev->mman.buffer_funcs_ring;
>>   	struct amdgpu_res_cursor src_mm, dst_mm;
>> @@ -363,9 +364,7 @@ int amdgpu_ttm_copy_mem_to_mem(struct amdgpu_device *adev,
>>   	}
>>   error:
>>   	mutex_unlock(&adev->mman.gtt_window_lock);
>> -	if (f)
>> -		*f = dma_fence_get(fence);
>> -	dma_fence_put(fence);
>> +	*f = fence;
>>   	return r;
>>   }
>>   
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
>> index bb17987f0447..07ae2853c77c 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
>> @@ -170,12 +170,6 @@ int amdgpu_copy_buffer(struct amdgpu_ring *ring, uint64_t src_offset,
>>   		       struct dma_resv *resv,
>>   		       struct dma_fence **fence, bool direct_submit,
>>   		       bool vm_needs_flush, uint32_t copy_flags);
>> -int amdgpu_ttm_copy_mem_to_mem(struct amdgpu_device *adev,
>> -			       const struct amdgpu_copy_mem *src,
>> -			       const struct amdgpu_copy_mem *dst,
>> -			       uint64_t size, bool tmz,
>> -			       struct dma_resv *resv,
>> -			       struct dma_fence **f);
>>   int amdgpu_ttm_clear_buffer(struct amdgpu_bo *bo,
>>   			    struct dma_resv *resv,
>>   			    struct dma_fence **fence);