Re: [RFC v2 03/13] dma-fence: Use a flag for 64-bit seqnos

["Christian König" <christian.koenig@amd.com>]

On 5/9/25 17:33, Tvrtko Ursulin wrote:
> With the goal of reducing the need for drivers to touch (and dereference)
> fence->ops, we move the 64-bit seqnos flag from struct dma_fence_ops to
> the fence->flags.
> 
> Drivers which were setting this flag are changed to use new
> dma_fence_init64() instead of dma_fence_init().
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>

My idea was to copy the flag from the ops during init, but that should work as well.

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>  drivers/dma-buf/dma-fence-chain.c                | 5 ++---
>  drivers/dma-buf/dma-fence.c                      | 9 +++++++++
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c | 5 ++---
>  include/linux/dma-fence.h                        | 6 +++++-
>  4 files changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
> index 90424f23fd73..a8a90acf4f34 100644
> --- a/drivers/dma-buf/dma-fence-chain.c
> +++ b/drivers/dma-buf/dma-fence-chain.c
> @@ -218,7 +218,6 @@ static void dma_fence_chain_set_deadline(struct dma_fence *fence,
>  }
>  
>  const struct dma_fence_ops dma_fence_chain_ops = {
> -	.use_64bit_seqno = true,
>  	.get_driver_name = dma_fence_chain_get_driver_name,
>  	.get_timeline_name = dma_fence_chain_get_timeline_name,
>  	.enable_signaling = dma_fence_chain_enable_signaling,
> @@ -262,8 +261,8 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
>  			seqno = max(prev->seqno, seqno);
>  	}
>  
> -	dma_fence_init(&chain->base, &dma_fence_chain_ops,
> -		       &chain->lock, context, seqno);
> +	dma_fence_init64(&chain->base, &dma_fence_chain_ops, &chain->lock,
> +			 context, seqno);
>  
>  	/*
>  	 * Chaining dma_fence_chain container together is only allowed through
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index f0cdd3e99d36..33661658f684 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -1023,3 +1023,12 @@ dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
>  	trace_dma_fence_init(fence);
>  }
>  EXPORT_SYMBOL(dma_fence_init);
> +
> +void
> +dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops,
> +		 spinlock_t *lock, u64 context, u64 seqno)
> +{
> +	dma_fence_init(fence, ops, lock, context, seqno);
> +	__set_bit(DMA_FENCE_FLAG_SEQNO64_BIT, &fence->flags);
> +}
> +EXPORT_SYMBOL(dma_fence_init64);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c
> index 51cddfa3f1e8..5d26797356a3 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c
> @@ -71,7 +71,6 @@ static void amdgpu_tlb_fence_work(struct work_struct *work)
>  }
>  
>  static const struct dma_fence_ops amdgpu_tlb_fence_ops = {
> -	.use_64bit_seqno = true,
>  	.get_driver_name = amdgpu_tlb_fence_get_driver_name,
>  	.get_timeline_name = amdgpu_tlb_fence_get_timeline_name
>  };
> @@ -101,8 +100,8 @@ void amdgpu_vm_tlb_fence_create(struct amdgpu_device *adev, struct amdgpu_vm *vm
>  	INIT_WORK(&f->work, amdgpu_tlb_fence_work);
>  	spin_lock_init(&f->lock);
>  
> -	dma_fence_init(&f->base, &amdgpu_tlb_fence_ops, &f->lock,
> -		       vm->tlb_fence_context, atomic64_read(&vm->tlb_seq));
> +	dma_fence_init64(&f->base, &amdgpu_tlb_fence_ops, &f->lock,
> +			 vm->tlb_fence_context, atomic64_read(&vm->tlb_seq));
>  
>  	/* TODO: We probably need a separate wq here */
>  	dma_fence_get(&f->base);
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 48b5202c531d..ac6535716dbe 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -97,6 +97,7 @@ struct dma_fence {
>  };
>  
>  enum dma_fence_flag_bits {
> +	DMA_FENCE_FLAG_SEQNO64_BIT,
>  	DMA_FENCE_FLAG_SIGNALED_BIT,
>  	DMA_FENCE_FLAG_TIMESTAMP_BIT,
>  	DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
> @@ -262,6 +263,9 @@ struct dma_fence_ops {
>  void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
>  		    spinlock_t *lock, u64 context, u64 seqno);
>  
> +void dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops,
> +		      spinlock_t *lock, u64 context, u64 seqno);
> +
>  void dma_fence_release(struct kref *kref);
>  void dma_fence_free(struct dma_fence *fence);
>  void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq);
> @@ -454,7 +458,7 @@ static inline bool __dma_fence_is_later(struct dma_fence *fence, u64 f1, u64 f2)
>  	 * 32bit sequence numbers. Use a 64bit compare when the driver says to
>  	 * do so.
>  	 */
> -	if (fence->ops->use_64bit_seqno)
> +	if (test_bit(DMA_FENCE_FLAG_SEQNO64_BIT, &fence->flags))
>  		return f1 > f2;
>  
>  	return (int)(lower_32_bits(f1) - lower_32_bits(f2)) > 0;