dma-fence: Polish kernel-doc for dma-fence.c
- Intro section that links to how this is exposed to userspace. - Lots more hyperlinks. - Minor clarifications and style polish v2: Add misplaced hunk of kerneldoc from a different patch. Reviewed-by: Christian König <christian.koenig@amd.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: Gustavo Padovan <gustavo@padovan.org> Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org Link: https://patchwork.freedesktop.org/patch/msgid/20180704092909.6599-6-daniel.vetter@ffwll.ch
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Daniel Vetter
parent
de10eba0f6
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4dd3cdb281
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@ -130,6 +130,12 @@ Reservation Objects
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DMA Fences
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----------
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.. kernel-doc:: drivers/dma-buf/dma-fence.c
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:doc: DMA fences overview
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DMA Fences Functions Reference
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. kernel-doc:: drivers/dma-buf/dma-fence.c
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:export:
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@ -39,11 +39,42 @@ EXPORT_TRACEPOINT_SYMBOL(dma_fence_enable_signal);
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static atomic64_t dma_fence_context_counter = ATOMIC64_INIT(0);
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/**
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* dma_fence_context_alloc - allocate an array of fence contexts
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* @num: [in] amount of contexts to allocate
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* DOC: DMA fences overview
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*
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* This function will return the first index of the number of fences allocated.
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* The fence context is used for setting fence->context to a unique number.
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* DMA fences, represented by &struct dma_fence, are the kernel internal
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* synchronization primitive for DMA operations like GPU rendering, video
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* encoding/decoding, or displaying buffers on a screen.
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*
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* A fence is initialized using dma_fence_init() and completed using
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* dma_fence_signal(). Fences are associated with a context, allocated through
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* dma_fence_context_alloc(), and all fences on the same context are
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* fully ordered.
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*
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* Since the purposes of fences is to facilitate cross-device and
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* cross-application synchronization, there's multiple ways to use one:
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*
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* - Individual fences can be exposed as a &sync_file, accessed as a file
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* descriptor from userspace, created by calling sync_file_create(). This is
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* called explicit fencing, since userspace passes around explicit
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* synchronization points.
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*
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* - Some subsystems also have their own explicit fencing primitives, like
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* &drm_syncobj. Compared to &sync_file, a &drm_syncobj allows the underlying
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* fence to be updated.
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*
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* - Then there's also implicit fencing, where the synchronization points are
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* implicitly passed around as part of shared &dma_buf instances. Such
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* implicit fences are stored in &struct reservation_object through the
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* &dma_buf.resv pointer.
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*/
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/**
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* dma_fence_context_alloc - allocate an array of fence contexts
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* @num: amount of contexts to allocate
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*
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* This function will return the first index of the number of fence contexts
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* allocated. The fence context is used for setting &dma_fence.context to a
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* unique number by passing the context to dma_fence_init().
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*/
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u64 dma_fence_context_alloc(unsigned num)
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{
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@ -59,10 +90,14 @@ EXPORT_SYMBOL(dma_fence_context_alloc);
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* Signal completion for software callbacks on a fence, this will unblock
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* dma_fence_wait() calls and run all the callbacks added with
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* dma_fence_add_callback(). Can be called multiple times, but since a fence
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* can only go from unsignaled to signaled state, it will only be effective
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* the first time.
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* can only go from the unsignaled to the signaled state and not back, it will
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* only be effective the first time.
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*
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* Unlike dma_fence_signal, this function must be called with fence->lock held.
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* Unlike dma_fence_signal(), this function must be called with &dma_fence.lock
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* held.
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*
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* Returns 0 on success and a negative error value when @fence has been
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* signalled already.
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*/
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int dma_fence_signal_locked(struct dma_fence *fence)
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{
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@ -102,8 +137,11 @@ EXPORT_SYMBOL(dma_fence_signal_locked);
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* Signal completion for software callbacks on a fence, this will unblock
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* dma_fence_wait() calls and run all the callbacks added with
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* dma_fence_add_callback(). Can be called multiple times, but since a fence
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* can only go from unsignaled to signaled state, it will only be effective
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* the first time.
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* can only go from the unsignaled to the signaled state and not back, it will
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* only be effective the first time.
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*
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* Returns 0 on success and a negative error value when @fence has been
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* signalled already.
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*/
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int dma_fence_signal(struct dma_fence *fence)
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{
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@ -136,9 +174,9 @@ EXPORT_SYMBOL(dma_fence_signal);
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/**
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* dma_fence_wait_timeout - sleep until the fence gets signaled
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* or until timeout elapses
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* @fence: [in] the fence to wait on
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* @intr: [in] if true, do an interruptible wait
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* @timeout: [in] timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
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* @fence: the fence to wait on
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* @intr: if true, do an interruptible wait
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* @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
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*
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* Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
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* remaining timeout in jiffies on success. Other error values may be
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@ -148,6 +186,8 @@ EXPORT_SYMBOL(dma_fence_signal);
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* directly or indirectly (buf-mgr between reservation and committing)
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* holds a reference to the fence, otherwise the fence might be
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* freed before return, resulting in undefined behavior.
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*
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* See also dma_fence_wait() and dma_fence_wait_any_timeout().
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*/
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signed long
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dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
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@ -167,6 +207,13 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
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}
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EXPORT_SYMBOL(dma_fence_wait_timeout);
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/**
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* dma_fence_release - default relese function for fences
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* @kref: &dma_fence.recfount
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*
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* This is the default release functions for &dma_fence. Drivers shouldn't call
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* this directly, but instead call dma_fence_put().
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*/
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void dma_fence_release(struct kref *kref)
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{
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struct dma_fence *fence =
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@ -184,6 +231,13 @@ void dma_fence_release(struct kref *kref)
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}
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EXPORT_SYMBOL(dma_fence_release);
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/**
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* dma_fence_free - default release function for &dma_fence.
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* @fence: fence to release
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*
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* This is the default implementation for &dma_fence_ops.release. It calls
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* kfree_rcu() on @fence.
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*/
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void dma_fence_free(struct dma_fence *fence)
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{
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kfree_rcu(fence, rcu);
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@ -192,10 +246,11 @@ EXPORT_SYMBOL(dma_fence_free);
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/**
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* dma_fence_enable_sw_signaling - enable signaling on fence
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* @fence: [in] the fence to enable
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* @fence: the fence to enable
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*
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* this will request for sw signaling to be enabled, to make the fence
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* complete as soon as possible
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* This will request for sw signaling to be enabled, to make the fence
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* complete as soon as possible. This calls &dma_fence_ops.enable_signaling
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* internally.
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*/
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void dma_fence_enable_sw_signaling(struct dma_fence *fence)
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{
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@ -220,24 +275,24 @@ EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
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/**
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* dma_fence_add_callback - add a callback to be called when the fence
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* is signaled
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* @fence: [in] the fence to wait on
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* @cb: [in] the callback to register
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* @func: [in] the function to call
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* @fence: the fence to wait on
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* @cb: the callback to register
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* @func: the function to call
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*
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* cb will be initialized by dma_fence_add_callback, no initialization
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* @cb will be initialized by dma_fence_add_callback(), no initialization
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* by the caller is required. Any number of callbacks can be registered
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* to a fence, but a callback can only be registered to one fence at a time.
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*
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* Note that the callback can be called from an atomic context. If
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* fence is already signaled, this function will return -ENOENT (and
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* *not* call the callback)
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* *not* call the callback).
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*
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* Add a software callback to the fence. Same restrictions apply to
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* refcount as it does to dma_fence_wait, however the caller doesn't need to
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* keep a refcount to fence afterwards: when software access is enabled,
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* the creator of the fence is required to keep the fence alive until
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* after it signals with dma_fence_signal. The callback itself can be called
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* from irq context.
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* refcount as it does to dma_fence_wait(), however the caller doesn't need to
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* keep a refcount to fence afterward dma_fence_add_callback() has returned:
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* when software access is enabled, the creator of the fence is required to keep
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* the fence alive until after it signals with dma_fence_signal(). The callback
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* itself can be called from irq context.
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*
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* Returns 0 in case of success, -ENOENT if the fence is already signaled
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* and -EINVAL in case of error.
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@ -286,7 +341,7 @@ EXPORT_SYMBOL(dma_fence_add_callback);
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/**
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* dma_fence_get_status - returns the status upon completion
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* @fence: [in] the dma_fence to query
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* @fence: the dma_fence to query
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*
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* This wraps dma_fence_get_status_locked() to return the error status
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* condition on a signaled fence. See dma_fence_get_status_locked() for more
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@ -311,8 +366,8 @@ EXPORT_SYMBOL(dma_fence_get_status);
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/**
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* dma_fence_remove_callback - remove a callback from the signaling list
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* @fence: [in] the fence to wait on
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* @cb: [in] the callback to remove
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* @fence: the fence to wait on
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* @cb: the callback to remove
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*
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* Remove a previously queued callback from the fence. This function returns
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* true if the callback is successfully removed, or false if the fence has
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@ -323,6 +378,9 @@ EXPORT_SYMBOL(dma_fence_get_status);
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* doing, since deadlocks and race conditions could occur all too easily. For
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* this reason, it should only ever be done on hardware lockup recovery,
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* with a reference held to the fence.
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*
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* Behaviour is undefined if @cb has not been added to @fence using
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* dma_fence_add_callback() beforehand.
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*/
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bool
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dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *cb)
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@ -359,9 +417,9 @@ dma_fence_default_wait_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
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/**
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* dma_fence_default_wait - default sleep until the fence gets signaled
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* or until timeout elapses
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* @fence: [in] the fence to wait on
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* @intr: [in] if true, do an interruptible wait
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* @timeout: [in] timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
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* @fence: the fence to wait on
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* @intr: if true, do an interruptible wait
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* @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
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*
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* Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
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* remaining timeout in jiffies on success. If timeout is zero the value one is
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@ -454,11 +512,11 @@ dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
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/**
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* dma_fence_wait_any_timeout - sleep until any fence gets signaled
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* or until timeout elapses
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* @fences: [in] array of fences to wait on
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* @count: [in] number of fences to wait on
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* @intr: [in] if true, do an interruptible wait
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* @timeout: [in] timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
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* @idx: [out] the first signaled fence index, meaningful only on
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* @fences: array of fences to wait on
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* @count: number of fences to wait on
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* @intr: if true, do an interruptible wait
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* @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
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* @idx: used to store the first signaled fence index, meaningful only on
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* positive return
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*
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* Returns -EINVAL on custom fence wait implementation, -ERESTARTSYS if
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@ -468,6 +526,8 @@ dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
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* Synchronous waits for the first fence in the array to be signaled. The
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* caller needs to hold a reference to all fences in the array, otherwise a
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* fence might be freed before return, resulting in undefined behavior.
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*
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* See also dma_fence_wait() and dma_fence_wait_timeout().
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*/
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signed long
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dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count,
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@ -540,19 +600,18 @@ EXPORT_SYMBOL(dma_fence_wait_any_timeout);
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/**
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* dma_fence_init - Initialize a custom fence.
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* @fence: [in] the fence to initialize
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* @ops: [in] the dma_fence_ops for operations on this fence
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* @lock: [in] the irqsafe spinlock to use for locking this fence
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* @context: [in] the execution context this fence is run on
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* @seqno: [in] a linear increasing sequence number for this context
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* @fence: the fence to initialize
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* @ops: the dma_fence_ops for operations on this fence
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* @lock: the irqsafe spinlock to use for locking this fence
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* @context: the execution context this fence is run on
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* @seqno: a linear increasing sequence number for this context
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*
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* Initializes an allocated fence, the caller doesn't have to keep its
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* refcount after committing with this fence, but it will need to hold a
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* refcount again if dma_fence_ops.enable_signaling gets called. This can
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* be used for other implementing other types of fence.
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* refcount again if &dma_fence_ops.enable_signaling gets called.
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*
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* context and seqno are used for easy comparison between fences, allowing
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* to check which fence is later by simply using dma_fence_later.
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* to check which fence is later by simply using dma_fence_later().
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*/
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void
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dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
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