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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
This commit is contained in:
Daniel Vetter 2018-07-04 11:29:09 +02:00
parent de10eba0f6
commit 4dd3cdb281
2 changed files with 110 additions and 45 deletions
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6
Documentation/driver-api/dma-buf.rst
View File

@ -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:

149
drivers/dma-buf/dma-fence.c
View File

@ -39,11 +39,42 @@ EXPORT_TRACEPOINT_SYMBOL(dma_fence_enable_signal);
static atomic64_t dma_fence_context_counter = ATOMIC64_INIT(0);
/**
* dma_fence_context_alloc - allocate an array of fence contexts
* @num: [in] amount of contexts to allocate
* DOC: DMA fences overview
*
* 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.
* 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: amount of contexts to allocate
*
* 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 fence->lock held.
* Unlike dma_fence_signal(), this function must be called with &dma_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,