[PATCH v4 2/9] dma-fence: Use a flag for 64-bit seqnos

Tvrtko Ursulin tvrtko.ursulin at igalia.com
Mon Jun 2 15:25:02 UTC 2025


On 02/06/2025 15:42, Christian König wrote:
> On 6/2/25 15:05, Tvrtko Ursulin wrote:
>>
>> Hi,
>>
>> On 15/05/2025 14:15, Christian König wrote:
>>> Hey drm-misc maintainers,
>>>
>>> can you guys please backmerge drm-next into drm-misc-next?
>>>
>>> I want to push this patch here but it depends on changes which are partially in drm-next and partially in drm-misc-next.
>>
>> Looks like the backmerge is still pending?
> 
> Yes, @Maarten, @Maxime and @Thomas ping on this.
> 
>> In the meantime, Christian, any chance you will have some bandwith to think about the tail end of the series? Specifically patch 6 and how that is used onward.
> 
> Well the RCU grace period is quite a nifty hack. I wanted to go over it again after merging the first patches from this series.
> 
> In general looks like a good idea to me, I just don't like that we explicitely need to expose dma_fence_access_begin() and dma_fence_access_end().
> 
> Especially we can't do that while calling fence->ops->release.

Hm why not? You think something will take offence of the rcu_read_lock()?

Regards,

Tvrtko

>>> On 5/15/25 11:49, 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().
>>>>
>>>> v2:
>>>>    * Streamlined init and added kerneldoc.
>>>>    * Rebase for amdgpu userq which landed since.
>>>>
>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>>>> Reviewed-by: Christian König <christian.koenig at amd.com> # v1
>>>> ---
>>>>    drivers/dma-buf/dma-fence-chain.c             |  5 +-
>>>>    drivers/dma-buf/dma-fence.c                   | 69 ++++++++++++++-----
>>>>    .../drm/amd/amdgpu/amdgpu_eviction_fence.c    |  7 +-
>>>>    .../gpu/drm/amd/amdgpu/amdgpu_userq_fence.c   |  5 +-
>>>>    .../gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c  |  5 +-
>>>>    include/linux/dma-fence.h                     | 14 ++--
>>>>    6 files changed, 64 insertions(+), 41 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..705b59787731 100644
>>>> --- a/drivers/dma-buf/dma-fence.c
>>>> +++ b/drivers/dma-buf/dma-fence.c
>>>> @@ -989,24 +989,9 @@ void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq)
>>>>    }
>>>>    EXPORT_SYMBOL(dma_fence_describe);
>>>>    -/**
>>>> - * dma_fence_init - Initialize a custom fence.
>>>> - * @fence: the fence to initialize
>>>> - * @ops: the dma_fence_ops for operations on this fence
>>>> - * @lock: the irqsafe spinlock to use for locking this fence
>>>> - * @context: the execution context this fence is run on
>>>> - * @seqno: a linear increasing sequence number for this context
>>>> - *
>>>> - * Initializes an allocated fence, the caller doesn't have to keep its
>>>> - * refcount after committing with this fence, but it will need to hold a
>>>> - * refcount again if &dma_fence_ops.enable_signaling gets called.
>>>> - *
>>>> - * context and seqno are used for easy comparison between fences, allowing
>>>> - * to check which fence is later by simply using dma_fence_later().
>>>> - */
>>>> -void
>>>> -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
>>>> -           spinlock_t *lock, u64 context, u64 seqno)
>>>> +static void
>>>> +__dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
>>>> +             spinlock_t *lock, u64 context, u64 seqno, unsigned long flags)
>>>>    {
>>>>        BUG_ON(!lock);
>>>>        BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name);
>>>> @@ -1017,9 +1002,55 @@ dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
>>>>        fence->lock = lock;
>>>>        fence->context = context;
>>>>        fence->seqno = seqno;
>>>> -    fence->flags = 0UL;
>>>> +    fence->flags = flags;
>>>>        fence->error = 0;
>>>>          trace_dma_fence_init(fence);
>>>>    }
>>>> +
>>>> +/**
>>>> + * dma_fence_init - Initialize a custom fence.
>>>> + * @fence: the fence to initialize
>>>> + * @ops: the dma_fence_ops for operations on this fence
>>>> + * @lock: the irqsafe spinlock to use for locking this fence
>>>> + * @context: the execution context this fence is run on
>>>> + * @seqno: a linear increasing sequence number for this context
>>>> + *
>>>> + * Initializes an allocated fence, the caller doesn't have to keep its
>>>> + * refcount after committing with this fence, but it will need to hold a
>>>> + * refcount again if &dma_fence_ops.enable_signaling gets called.
>>>> + *
>>>> + * context and seqno are used for easy comparison between fences, allowing
>>>> + * to check which fence is later by simply using dma_fence_later().
>>>> + */
>>>> +void
>>>> +dma_fence_init(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, 0UL);
>>>> +}
>>>>    EXPORT_SYMBOL(dma_fence_init);
>>>> +
>>>> +/**
>>>> + * dma_fence_init64 - Initialize a custom fence with 64-bit seqno support.
>>>> + * @fence: the fence to initialize
>>>> + * @ops: the dma_fence_ops for operations on this fence
>>>> + * @lock: the irqsafe spinlock to use for locking this fence
>>>> + * @context: the execution context this fence is run on
>>>> + * @seqno: a linear increasing sequence number for this context
>>>> + *
>>>> + * Initializes an allocated fence, the caller doesn't have to keep its
>>>> + * refcount after committing with this fence, but it will need to hold a
>>>> + * refcount again if &dma_fence_ops.enable_signaling gets called.
>>>> + *
>>>> + * Context and seqno are used for easy comparison between fences, allowing
>>>> + * to check which fence is later by simply using dma_fence_later().
>>>> + */
>>>> +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,
>>>> +             BIT(DMA_FENCE_FLAG_SEQNO64_BIT));
>>>> +}
>>>> +EXPORT_SYMBOL(dma_fence_init64);
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c
>>>> index 1a7469543db5..79713421bffe 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c
>>>> @@ -134,7 +134,6 @@ static bool amdgpu_eviction_fence_enable_signaling(struct dma_fence *f)
>>>>    }
>>>>      static const struct dma_fence_ops amdgpu_eviction_fence_ops = {
>>>> -    .use_64bit_seqno = true,
>>>>        .get_driver_name = amdgpu_eviction_fence_get_driver_name,
>>>>        .get_timeline_name = amdgpu_eviction_fence_get_timeline_name,
>>>>        .enable_signaling = amdgpu_eviction_fence_enable_signaling,
>>>> @@ -160,9 +159,9 @@ amdgpu_eviction_fence_create(struct amdgpu_eviction_fence_mgr *evf_mgr)
>>>>        ev_fence->evf_mgr = evf_mgr;
>>>>        get_task_comm(ev_fence->timeline_name, current);
>>>>        spin_lock_init(&ev_fence->lock);
>>>> -    dma_fence_init(&ev_fence->base, &amdgpu_eviction_fence_ops,
>>>> -               &ev_fence->lock, evf_mgr->ev_fence_ctx,
>>>> -               atomic_inc_return(&evf_mgr->ev_fence_seq));
>>>> +    dma_fence_init64(&ev_fence->base, &amdgpu_eviction_fence_ops,
>>>> +             &ev_fence->lock, evf_mgr->ev_fence_ctx,
>>>> +             atomic_inc_return(&evf_mgr->ev_fence_seq));
>>>>        return ev_fence;
>>>>    }
>>>>    diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
>>>> index 029cb24c28b3..5e92d00a591f 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
>>>> @@ -239,8 +239,8 @@ static int amdgpu_userq_fence_create(struct amdgpu_usermode_queue *userq,
>>>>        fence = &userq_fence->base;
>>>>        userq_fence->fence_drv = fence_drv;
>>>>    -    dma_fence_init(fence, &amdgpu_userq_fence_ops, &userq_fence->lock,
>>>> -               fence_drv->context, seq);
>>>> +    dma_fence_init64(fence, &amdgpu_userq_fence_ops, &userq_fence->lock,
>>>> +             fence_drv->context, seq);
>>>>          amdgpu_userq_fence_driver_get(fence_drv);
>>>>        dma_fence_get(fence);
>>>> @@ -334,7 +334,6 @@ static void amdgpu_userq_fence_release(struct dma_fence *f)
>>>>    }
>>>>      static const struct dma_fence_ops amdgpu_userq_fence_ops = {
>>>> -    .use_64bit_seqno = true,
>>>>        .get_driver_name = amdgpu_userq_fence_get_driver_name,
>>>>        .get_timeline_name = amdgpu_userq_fence_get_timeline_name,
>>>>        .signaled = amdgpu_userq_fence_signaled,
>>>> 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..a34a0dcdc446 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,
>>>> @@ -124,14 +125,6 @@ struct dma_fence_cb {
>>>>     *
>>>>     */
>>>>    struct dma_fence_ops {
>>>> -    /**
>>>> -     * @use_64bit_seqno:
>>>> -     *
>>>> -     * True if this dma_fence implementation uses 64bit seqno, false
>>>> -     * otherwise.
>>>> -     */
>>>> -    bool use_64bit_seqno;
>>>> -
>>>>        /**
>>>>         * @get_driver_name:
>>>>         *
>>>> @@ -262,6 +255,9 @@ 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 +450,7 @@ 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;
>>>
>>
> 



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