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    Subject[PATCH 1/2] dma-buf/dma-fence: Add dma_fence_init_noref()
    Date
    From: Rob Clark <robdclark@chromium.org>

    Add a way to initialize a fence without touching the refcount. This is
    useful, for example, if the fence is embedded in a drm_sched_job. In
    this case the refcount will be initialized before the job is queued.
    But the seqno of the hw_fence is not known until job_run().

    Signed-off-by: Rob Clark <robdclark@chromium.org>
    ---
    drivers/dma-buf/dma-fence.c | 43 ++++++++++++++++++++++++++++---------
    include/linux/dma-fence.h | 2 ++
    2 files changed, 35 insertions(+), 10 deletions(-)

    diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
    index 74e36f6d05b0..97c05a465cb4 100644
    --- a/drivers/dma-buf/dma-fence.c
    +++ b/drivers/dma-buf/dma-fence.c
    @@ -989,28 +989,27 @@ void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq)
    EXPORT_SYMBOL(dma_fence_describe);

    /**
    - * dma_fence_init - Initialize a custom fence.
    + * dma_fence_init_noref - Initialize a custom fence without initializing refcount.
    * @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().
    + * Like &dma_fence_init but does not initialize the refcount. Suitable
    + * for cases where the fence is embedded in another struct which has it's
    + * refcount initialized before the fence is initialized. Such as embedding
    + * in a &drm_sched_job, where the job is created before knowing the seqno
    + * of the hw_fence.
    */
    void
    -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
    - spinlock_t *lock, u64 context, u64 seqno)
    +dma_fence_init_noref(struct dma_fence *fence, const struct dma_fence_ops *ops,
    + spinlock_t *lock, u64 context, u64 seqno)
    {
    BUG_ON(!lock);
    BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name);
    + BUG_ON(!kref_read(&fence->refcount));

    - kref_init(&fence->refcount);
    fence->ops = ops;
    INIT_LIST_HEAD(&fence->cb_list);
    fence->lock = lock;
    @@ -1021,4 +1020,28 @@ dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,

    trace_dma_fence_init(fence);
    }
    +EXPORT_SYMBOL(dma_fence_init_noref);
    +
    +/**
    + * 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)
    +{
    + kref_init(&fence->refcount);
    + dma_fence_init_noref(fence, ops, lock, context, seqno);
    +}
    EXPORT_SYMBOL(dma_fence_init);
    diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
    index d54b595a0fe0..f617c78a2e0a 100644
    --- a/include/linux/dma-fence.h
    +++ b/include/linux/dma-fence.h
    @@ -279,6 +279,8 @@ struct dma_fence_ops {
    void (*set_deadline)(struct dma_fence *fence, ktime_t deadline);
    };

    +void dma_fence_init_noref(struct dma_fence *fence, const struct dma_fence_ops *ops,
    + spinlock_t *lock, u64 context, u64 seqno);
    void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
    spinlock_t *lock, u64 context, u64 seqno);

    --
    2.39.2
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