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

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Message-ID: <3b4f8837-e0a8-4e8c-9d33-5f107e41c55d@damsy.net>
Date: Tue, 16 Sep 2025 13:58:04 +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 12:52, Christian König a écrit :
> On 16.09.25 11:46, Pierre-Eric Pelloux-Prayer wrote:
>>
>>
>> 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
> 
> Never seen that before. Is that gcc specifc or standardized?

clang supports it:

https://clang.llvm.org/docs/AttributeReference.html#id10

And both syntaxes are already used in the drm subtree by i915.

Pierre-Eric

> 
>>
>>
>>>
>>> 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.
> 
> Yeah it's clearly useful, but I'm worried that clang won't like it.
> 
> Christian.
> 
>>
>> 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);
>