[PATCH 5/5] dma-fence: Polish kernel-doc for dma-fence.c
Christian König
ckoenig.leichtzumerken at gmail.com
Wed Jul 4 09:36:26 UTC 2018
Am 04.07.2018 um 11:29 schrieb Daniel Vetter:
> - 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.
>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: Gustavo Padovan <gustavo at padovan.org>
> Cc: linux-media at vger.kernel.org
> Cc: linaro-mm-sig at lists.linaro.org
Reviewed-by: Christian König <christian.koenig at amd.com>
> ---
> Documentation/driver-api/dma-buf.rst | 6 ++
> drivers/dma-buf/dma-fence.c | 147 +++++++++++++++++++--------
> 2 files changed, 109 insertions(+), 44 deletions(-)
>
> diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
> index dc384f2f7f34..b541e97c7ab1 100644
> --- a/Documentation/driver-api/dma-buf.rst
> +++ b/Documentation/driver-api/dma-buf.rst
> @@ -130,6 +130,12 @@ Reservation Objects
> DMA Fences
> ----------
>
> +.. kernel-doc:: drivers/dma-buf/dma-fence.c
> + :doc: DMA fences overview
> +
> +DMA Fences Functions Reference
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> .. kernel-doc:: drivers/dma-buf/dma-fence.c
> :export:
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 7a92f85a4cec..1551ca7df394 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -38,12 +38,43 @@ EXPORT_TRACEPOINT_SYMBOL(dma_fence_enable_signal);
> */
> static atomic64_t dma_fence_context_counter = ATOMIC64_INIT(0);
>
> +/**
> + * DOC: DMA fences overview
> + *
> + * DMA fences, represented by &struct dma_fence, are the kernel internal
> + * synchronization primitive for DMA operations like GPU rendering, video
> + * encoding/decoding, or displaying buffers on a screen.
> + *
> + * A fence is initialized using dma_fence_init() and completed using
> + * dma_fence_signal(). Fences are associated with a context, allocated through
> + * dma_fence_context_alloc(), and all fences on the same context are
> + * fully ordered.
> + *
> + * Since the purposes of fences is to facilitate cross-device and
> + * cross-application synchronization, there's multiple ways to use one:
> + *
> + * - Individual fences can be exposed as a &sync_file, accessed as a file
> + * descriptor from userspace, created by calling sync_file_create(). This is
> + * called explicit fencing, since userspace passes around explicit
> + * synchronization points.
> + *
> + * - Some subsystems also have their own explicit fencing primitives, like
> + * &drm_syncobj. Compared to &sync_file, a &drm_syncobj allows the underlying
> + * fence to be updated.
> + *
> + * - Then there's also implicit fencing, where the synchronization points are
> + * implicitly passed around as part of shared &dma_buf instances. Such
> + * implicit fences are stored in &struct reservation_object through the
> + * &dma_buf.resv pointer.
> + */
> +
> /**
> * dma_fence_context_alloc - allocate an array of fence contexts
> - * @num: [in] amount of contexts to allocate
> + * @num: amount of contexts to allocate
> *
> - * This function will return the first index of the number of fences allocated.
> - * The fence context is used for setting fence->context to a unique number.
> + * This function will return the first index of the number of fence contexts
> + * allocated. The fence context is used for setting &dma_fence.context to a
> + * unique number by passing the context to dma_fence_init().
> */
> u64 dma_fence_context_alloc(unsigned num)
> {
> @@ -59,10 +90,14 @@ EXPORT_SYMBOL(dma_fence_context_alloc);
> * Signal completion for software callbacks on a fence, this will unblock
> * dma_fence_wait() calls and run all the callbacks added with
> * dma_fence_add_callback(). Can be called multiple times, but since a fence
> - * can only go from unsignaled to signaled state, it will only be effective
> - * the first time.
> + * can only go from the unsignaled to the signaled state and not back, it will
> + * only be effective the first time.
> + *
> + * Unlike dma_fence_signal(), this function must be called with &dma_fence.lock
> + * held.
> *
> - * Unlike dma_fence_signal, this function must be called with fence->lock held.
> + * Returns 0 on success and a negative error value when @fence has been
> + * signalled already.
> */
> int dma_fence_signal_locked(struct dma_fence *fence)
> {
> @@ -102,8 +137,11 @@ EXPORT_SYMBOL(dma_fence_signal_locked);
> * Signal completion for software callbacks on a fence, this will unblock
> * dma_fence_wait() calls and run all the callbacks added with
> * dma_fence_add_callback(). Can be called multiple times, but since a fence
> - * can only go from unsignaled to signaled state, it will only be effective
> - * the first time.
> + * can only go from the unsignaled to the signaled state and not back, it will
> + * only be effective the first time.
> + *
> + * Returns 0 on success and a negative error value when @fence has been
> + * signalled already.
> */
> int dma_fence_signal(struct dma_fence *fence)
> {
> @@ -136,9 +174,9 @@ EXPORT_SYMBOL(dma_fence_signal);
> /**
> * dma_fence_wait_timeout - sleep until the fence gets signaled
> * or until timeout elapses
> - * @fence: [in] the fence to wait on
> - * @intr: [in] if true, do an interruptible wait
> - * @timeout: [in] timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
> + * @fence: the fence to wait on
> + * @intr: if true, do an interruptible wait
> + * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
> *
> * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
> * remaining timeout in jiffies on success. Other error values may be
> @@ -148,6 +186,8 @@ EXPORT_SYMBOL(dma_fence_signal);
> * directly or indirectly (buf-mgr between reservation and committing)
> * holds a reference to the fence, otherwise the fence might be
> * freed before return, resulting in undefined behavior.
> + *
> + * See also dma_fence_wait() and dma_fence_wait_any_timeout().
> */
> signed long
> dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
> @@ -167,6 +207,13 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
> }
> EXPORT_SYMBOL(dma_fence_wait_timeout);
>
> +/**
> + * dma_fence_release - default relese function for fences
> + * @kref: &dma_fence.recfount
> + *
> + * This is the default release functions for &dma_fence. Drivers shouldn't call
> + * this directly, but instead call dma_fence_put().
> + */
> void dma_fence_release(struct kref *kref)
> {
> struct dma_fence *fence =
> @@ -184,6 +231,13 @@ void dma_fence_release(struct kref *kref)
> }
> EXPORT_SYMBOL(dma_fence_release);
>
> +/**
> + * dma_fence_free - default release function for &dma_fence.
> + * @fence: fence to release
> + *
> + * This is the default implementation for &dma_fence_ops.release. It calls
> + * kfree_rcu() on @fence.
> + */
> void dma_fence_free(struct dma_fence *fence)
> {
> kfree_rcu(fence, rcu);
> @@ -192,10 +246,11 @@ EXPORT_SYMBOL(dma_fence_free);
>
> /**
> * dma_fence_enable_sw_signaling - enable signaling on fence
> - * @fence: [in] the fence to enable
> + * @fence: the fence to enable
> *
> - * this will request for sw signaling to be enabled, to make the fence
> - * complete as soon as possible
> + * This will request for sw signaling to be enabled, to make the fence
> + * complete as soon as possible. This calls &dma_fence_ops.enable_signaling
> + * internally.
> */
> void dma_fence_enable_sw_signaling(struct dma_fence *fence)
> {
> @@ -220,24 +275,24 @@ EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
> /**
> * dma_fence_add_callback - add a callback to be called when the fence
> * is signaled
> - * @fence: [in] the fence to wait on
> - * @cb: [in] the callback to register
> - * @func: [in] the function to call
> + * @fence: the fence to wait on
> + * @cb: the callback to register
> + * @func: the function to call
> *
> - * cb will be initialized by dma_fence_add_callback, no initialization
> + * @cb will be initialized by dma_fence_add_callback(), no initialization
> * by the caller is required. Any number of callbacks can be registered
> * to a fence, but a callback can only be registered to one fence at a time.
> *
> * Note that the callback can be called from an atomic context. If
> * fence is already signaled, this function will return -ENOENT (and
> - * *not* call the callback)
> + * *not* call the callback).
> *
> * Add a software callback to the fence. Same restrictions apply to
> - * refcount as it does to dma_fence_wait, however the caller doesn't need to
> - * keep a refcount to fence afterwards: when software access is enabled,
> - * the creator of the fence is required to keep the fence alive until
> - * after it signals with dma_fence_signal. The callback itself can be called
> - * from irq context.
> + * refcount as it does to dma_fence_wait(), however the caller doesn't need to
> + * keep a refcount to fence afterward dma_fence_add_callback() has returned:
> + * when software access is enabled, the creator of the fence is required to keep
> + * the fence alive until after it signals with dma_fence_signal(). The callback
> + * itself can be called from irq context.
> *
> * Returns 0 in case of success, -ENOENT if the fence is already signaled
> * and -EINVAL in case of error.
> @@ -286,7 +341,7 @@ EXPORT_SYMBOL(dma_fence_add_callback);
>
> /**
> * dma_fence_get_status - returns the status upon completion
> - * @fence: [in] the dma_fence to query
> + * @fence: the dma_fence to query
> *
> * This wraps dma_fence_get_status_locked() to return the error status
> * condition on a signaled fence. See dma_fence_get_status_locked() for more
> @@ -311,8 +366,8 @@ EXPORT_SYMBOL(dma_fence_get_status);
>
> /**
> * dma_fence_remove_callback - remove a callback from the signaling list
> - * @fence: [in] the fence to wait on
> - * @cb: [in] the callback to remove
> + * @fence: the fence to wait on
> + * @cb: the callback to remove
> *
> * Remove a previously queued callback from the fence. This function returns
> * true if the callback is successfully removed, or false if the fence has
> @@ -323,6 +378,9 @@ EXPORT_SYMBOL(dma_fence_get_status);
> * doing, since deadlocks and race conditions could occur all too easily. For
> * this reason, it should only ever be done on hardware lockup recovery,
> * with a reference held to the fence.
> + *
> + * Behaviour is undefined if @cb has not been added to @fence using
> + * dma_fence_add_callback() beforehand.
> */
> bool
> dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *cb)
> @@ -359,9 +417,9 @@ dma_fence_default_wait_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
> /**
> * dma_fence_default_wait - default sleep until the fence gets signaled
> * or until timeout elapses
> - * @fence: [in] the fence to wait on
> - * @intr: [in] if true, do an interruptible wait
> - * @timeout: [in] timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
> + * @fence: the fence to wait on
> + * @intr: if true, do an interruptible wait
> + * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
> *
> * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
> * remaining timeout in jiffies on success. If timeout is zero the value one is
> @@ -454,12 +512,12 @@ dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
> /**
> * dma_fence_wait_any_timeout - sleep until any fence gets signaled
> * or until timeout elapses
> - * @fences: [in] array of fences to wait on
> - * @count: [in] number of fences to wait on
> - * @intr: [in] if true, do an interruptible wait
> - * @timeout: [in] timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
> - * @idx: [out] the first signaled fence index, meaningful only on
> - * positive return
> + * @fences: array of fences to wait on
> + * @count: number of fences to wait on
> + * @intr: if true, do an interruptible wait
> + * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
> + * @idx: used to store the first signaled fence index, meaningful only on
> + * positive return
> *
> * Returns -EINVAL on custom fence wait implementation, -ERESTARTSYS if
> * interrupted, 0 if the wait timed out, or the remaining timeout in jiffies
> @@ -468,6 +526,8 @@ dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
> * Synchronous waits for the first fence in the array to be signaled. The
> * caller needs to hold a reference to all fences in the array, otherwise a
> * fence might be freed before return, resulting in undefined behavior.
> + *
> + * See also dma_fence_wait() and dma_fence_wait_timeout().
> */
> signed long
> dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count,
> @@ -540,19 +600,18 @@ EXPORT_SYMBOL(dma_fence_wait_any_timeout);
>
> /**
> * dma_fence_init - Initialize a custom fence.
> - * @fence: [in] the fence to initialize
> - * @ops: [in] the dma_fence_ops for operations on this fence
> - * @lock: [in] the irqsafe spinlock to use for locking this fence
> - * @context: [in] the execution context this fence is run on
> - * @seqno: [in] a linear increasing sequence number for this context
> + * @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. This can
> - * be used for other implementing other types of fence.
> + * 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.
> + * 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,
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