Re: [PATCH 1/6] fence: dma-buf cross-device synchronization (v17)

[Rob Clark]

On Mon, Feb 17, 2014 at 10:55 AM, Maarten Lankhorst
<maarten.lankhorst@xxxxxxxxxxxxx> wrote:
> A fence can be attached to a buffer which is being filled or consumed
> by hw, to allow userspace to pass the buffer without waiting to another
> device.  For example, userspace can call page_flip ioctl to display the
> next frame of graphics after kicking the GPU but while the GPU is still
> rendering.  The display device sharing the buffer with the GPU would
> attach a callback to get notified when the GPU's rendering-complete IRQ
> fires, to update the scan-out address of the display, without having to
> wake up userspace.
>
> A driver must allocate a fence context for each execution ring that can
> run in parallel. The function for this takes an argument with how many
> contexts to allocate:
>   + fence_context_alloc()
>
> A fence is transient, one-shot deal.  It is allocated and attached
> to one or more dma-buf's.  When the one that attached it is done, with
> the pending operation, it can signal the fence:
>   + fence_signal()
>
> To have a rough approximation whether a fence is fired, call:
>   + fence_is_signaled()
>
> The dma-buf-mgr handles tracking, and waiting on, the fences associated
> with a dma-buf.
>
> The one pending on the fence can add an async callback:
>   + fence_add_callback()
>
> The callback can optionally be cancelled with:
>   + fence_remove_callback()
>
> To wait synchronously, optionally with a timeout:
>   + fence_wait()
>   + fence_wait_timeout()
>
> When emitting a fence, call:
>   + trace_fence_emit()
>
> To annotate that a fence is blocking on another fence, call:
>   + trace_fence_annotate_wait_on(fence, on_fence)
>
> A default software-only implementation is provided, which can be used
> by drivers attaching a fence to a buffer when they have no other means
> for hw sync.  But a memory backed fence is also envisioned, because it
> is common that GPU's can write to, or poll on some memory location for
> synchronization.  For example:
>
>   fence = custom_get_fence(...);
>   if ((seqno_fence = to_seqno_fence(fence)) != NULL) {
>     dma_buf *fence_buf = seqno_fence->sync_buf;
>     get_dma_buf(fence_buf);
>
>     ... tell the hw the memory location to wait ...
>     custom_wait_on(fence_buf, seqno_fence->seqno_ofs, fence->seqno);
>   } else {
>     /* fall-back to sw sync * /
>     fence_add_callback(fence, my_cb);
>   }
>
> On SoC platforms, if some other hw mechanism is provided for synchronizing
> between IP blocks, it could be supported as an alternate implementation
> with it's own fence ops in a similar way.
>
> enable_signaling callback is used to provide sw signaling in case a cpu
> waiter is requested or no compatible hardware signaling could be used.
>
> The intention is to provide a userspace interface (presumably via eventfd)
> later, to be used in conjunction with dma-buf's mmap support for sw access
> to buffers (or for userspace apps that would prefer to do their own
> synchronization).
>
> v1: Original
> v2: After discussion w/ danvet and mlankhorst on #dri-devel, we decided
>     that dma-fence didn't need to care about the sw->hw signaling path
>     (it can be handled same as sw->sw case), and therefore the fence->ops
>     can be simplified and more handled in the core.  So remove the signal,
>     add_callback, cancel_callback, and wait ops, and replace with a simple
>     enable_signaling() op which can be used to inform a fence supporting
>     hw->hw signaling that one or more devices which do not support hw
>     signaling are waiting (and therefore it should enable an irq or do
>     whatever is necessary in order that the CPU is notified when the
>     fence is passed).
> v3: Fix locking fail in attach_fence() and get_fence()
> v4: Remove tie-in w/ dma-buf..  after discussion w/ danvet and mlankorst
>     we decided that we need to be able to attach one fence to N dma-buf's,
>     so using the list_head in dma-fence struct would be problematic.
> v5: [ Maarten Lankhorst ] Updated for dma-bikeshed-fence and dma-buf-manager.
> v6: [ Maarten Lankhorst ] I removed dma_fence_cancel_callback and some comments
>     about checking if fence fired or not. This is broken by design.
>     waitqueue_active during destruction is now fatal, since the signaller
>     should be holding a reference in enable_signalling until it signalled
>     the fence. Pass the original dma_fence_cb along, and call __remove_wait
>     in the dma_fence_callback handler, so that no cleanup needs to be
>     performed.
> v7: [ Maarten Lankhorst ] Set cb->func and only enable sw signaling if
>     fence wasn't signaled yet, for example for hardware fences that may
>     choose to signal blindly.
> v8: [ Maarten Lankhorst ] Tons of tiny fixes, moved __dma_fence_init to
>     header and fixed include mess. dma-fence.h now includes dma-buf.h
>     All members are now initialized, so kmalloc can be used for
>     allocating a dma-fence. More documentation added.
> v9: Change compiler bitfields to flags, change return type of
>     enable_signaling to bool. Rework dma_fence_wait. Added
>     dma_fence_is_signaled and dma_fence_wait_timeout.
>     s/dma// and change exports to non GPL. Added fence_is_signaled and
>     fence_enable_sw_signaling calls, add ability to override default
>     wait operation.
> v10: remove event_queue, use a custom list, export try_to_wake_up from
>     scheduler. Remove fence lock and use a global spinlock instead,
>     this should hopefully remove all the locking headaches I was having
>     on trying to implement this. enable_signaling is called with this
>     lock held.
> v11:
>     Use atomic ops for flags, lifting the need for some spin_lock_irqsaves.
>     However I kept the guarantee that after fence_signal returns, it is
>     guaranteed that enable_signaling has either been called to completion,
>     or will not be called any more.
>
>     Add contexts and seqno to base fence implementation. This allows you
>     to wait for less fences, by testing for seqno + signaled, and then only
>     wait on the later fence.
>
>     Add FENCE_TRACE, FENCE_WARN, and FENCE_ERR. This makes debugging easier.
>     An CONFIG_DEBUG_FENCE will be added to turn off the FENCE_TRACE
>     spam, and another runtime option can turn it off at runtime.
> v12:
>     Add CONFIG_FENCE_TRACE. Add missing documentation for the fence->context
>     and fence->seqno members.
> v13:
>     Fixup CONFIG_FENCE_TRACE kconfig description.
>     Move fence_context_alloc to fence.
>     Simplify fence_later.
>     Kill priv member to fence_cb.
> v14:
>     Remove priv argument from fence_add_callback, oops!
> v15:
>     Remove priv from documentation.
>     Explicitly include linux/atomic.h.
> v16:
>     Add trace events.
>     Import changes required by android syncpoints.
> v17:
>     Use wake_up_state instead of try_to_wake_up. (Colin Cross)
>     Fix up commit description for seqno_fence. (Rob Clark)
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>

Reviewed-by: Rob Clark <robdclark@xxxxxxxxx>


> ---
>  Documentation/DocBook/device-drivers.tmpl |    2
>  drivers/base/Kconfig                      |    9 +
>  drivers/base/Makefile                     |    2
>  drivers/base/fence.c                      |  415 +++++++++++++++++++++++++++++
>  include/linux/fence.h                     |  329 +++++++++++++++++++++++
>  include/trace/events/fence.h              |  125 +++++++++
>  6 files changed, 881 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/base/fence.c
>  create mode 100644 include/linux/fence.h
>  create mode 100644 include/trace/events/fence.h
>
> diff --git a/Documentation/DocBook/device-drivers.tmpl b/Documentation/DocBook/device-drivers.tmpl
> index f5170082bdb3..7a0c9ddb4818 100644
> --- a/Documentation/DocBook/device-drivers.tmpl
> +++ b/Documentation/DocBook/device-drivers.tmpl
> @@ -129,6 +129,8 @@ X!Edrivers/base/interface.c
>       </sect1>
>       <sect1><title>Device Drivers DMA Management</title>
>  !Edrivers/base/dma-buf.c
> +!Edrivers/base/fence.c
> +!Iinclude/linux/fence.h
>  !Edrivers/base/reservation.c
>  !Iinclude/linux/reservation.h
>  !Edrivers/base/dma-coherent.c
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index ec36e7772e57..b50ad30151ae 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -200,6 +200,15 @@ config DMA_SHARED_BUFFER
>           APIs extension; the file's descriptor can then be passed on to other
>           driver.
>
> +config FENCE_TRACE
> +       bool "Enable verbose FENCE_TRACE messages"
> +       depends on DMA_SHARED_BUFFER
> +       help
> +         Enable the FENCE_TRACE printks. This will add extra
> +         spam to the console log, but will make it easier to diagnose
> +         lockup related problems for dma-buffers shared across multiple
> +         devices.
> +
>  config DMA_CMA
>         bool "DMA Contiguous Memory Allocator"
>         depends on HAVE_DMA_CONTIGUOUS && CMA
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 04b314e0fa51..eb4864aee073 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -10,7 +10,7 @@ obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
>  obj-y                  += power/
>  obj-$(CONFIG_HAS_DMA)  += dma-mapping.o
>  obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
> -obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o reservation.o
> +obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o fence.o reservation.o
>  obj-$(CONFIG_ISA)      += isa.o
>  obj-$(CONFIG_FW_LOADER)        += firmware_class.o
>  obj-$(CONFIG_NUMA)     += node.o
> diff --git a/drivers/base/fence.c b/drivers/base/fence.c
> new file mode 100644
> index 000000000000..12df2bf62034
> --- /dev/null
> +++ b/drivers/base/fence.c
> @@ -0,0 +1,415 @@
> +/*
> + * Fence mechanism for dma-buf and to allow for asynchronous dma access
> + *
> + * Copyright (C) 2012 Canonical Ltd
> + * Copyright (C) 2012 Texas Instruments
> + *
> + * Authors:
> + * Rob Clark <robdclark@xxxxxxxxx>
> + * Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/slab.h>
> +#include <linux/export.h>
> +#include <linux/atomic.h>
> +#include <linux/fence.h>
> +
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/fence.h>
> +
> +EXPORT_TRACEPOINT_SYMBOL(fence_annotate_wait_on);
> +EXPORT_TRACEPOINT_SYMBOL(fence_emit);
> +
> +/**
> + * fence context counter: each execution context should have its own
> + * fence context, this allows checking if fences belong to the same
> + * context or not. One device can have multiple separate contexts,
> + * and they're used if some engine can run independently of another.
> + */
> +static atomic_t fence_context_counter = ATOMIC_INIT(0);
> +
> +/**
> + * fence_context_alloc - allocate an array of fence contexts
> + * @num:       [in]    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.
> + */
> +unsigned fence_context_alloc(unsigned num)
> +{
> +       BUG_ON(!num);
> +       return atomic_add_return(num, &fence_context_counter) - num;
> +}
> +EXPORT_SYMBOL(fence_context_alloc);
> +
> +int __fence_signal(struct fence *fence)
> +{
> +       struct fence_cb *cur, *tmp;
> +       int ret = 0;
> +
> +       if (WARN_ON(!fence))
> +               return -EINVAL;
> +
> +       if (!ktime_to_ns(fence->timestamp)) {
> +               fence->timestamp = ktime_get();
> +               smp_mb__before_clear_bit();
> +       }
> +
> +       if (test_and_set_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> +               ret = -EINVAL;
> +
> +               /*
> +                * we might have raced with the unlocked fence_signal,
> +                * still run through all callbacks
> +                */
> +       } else
> +               trace_fence_signaled(fence);
> +
> +       list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
> +               list_del_init(&cur->node);
> +               cur->func(fence, cur);
> +       }
> +       return ret;
> +}
> +EXPORT_SYMBOL(__fence_signal);
> +
> +/**
> + * fence_signal - signal completion of a fence
> + * @fence: the fence to signal
> + *
> + * Signal completion for software callbacks on a fence, this will unblock
> + * fence_wait() calls and run all the callbacks added with
> + * 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.
> + */
> +int fence_signal(struct fence *fence)
> +{
> +       unsigned long flags;
> +
> +       if (!fence)
> +               return -EINVAL;
> +
> +       if (!ktime_to_ns(fence->timestamp)) {
> +               fence->timestamp = ktime_get();
> +               smp_mb__before_clear_bit();
> +       }
> +
> +       if (test_and_set_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +               return -EINVAL;
> +
> +       trace_fence_signaled(fence);
> +
> +       if (test_bit(FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) {
> +               struct fence_cb *cur, *tmp;
> +
> +               spin_lock_irqsave(fence->lock, flags);
> +               list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
> +                       list_del_init(&cur->node);
> +                       cur->func(fence, cur);
> +               }
> +               spin_unlock_irqrestore(fence->lock, flags);
> +       }
> +       return 0;
> +}
> +EXPORT_SYMBOL(fence_signal);
> +
> +/**
> + * 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
> + *
> + * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
> + * remaining timeout in jiffies on success. Other error values may be
> + * returned on custom implementations.
> + *
> + * Performs a synchronous wait on this fence. It is assumed the caller
> + * 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.
> + */
> +long
> +fence_wait_timeout(struct fence *fence, bool intr, signed long timeout)
> +{
> +       unsigned long ret;
> +
> +       if (WARN_ON(timeout < 0))
> +               return -EINVAL;
> +
> +       trace_fence_wait_start(fence);
> +       ret = fence->ops->wait(fence, intr, timeout);
> +       trace_fence_wait_end(fence);
> +       return ret;
> +}
> +EXPORT_SYMBOL(fence_wait_timeout);
> +
> +void release_fence(struct kref *kref)
> +{
> +       struct fence *fence =
> +                       container_of(kref, struct fence, refcount);
> +
> +       trace_fence_destroy(fence);
> +
> +       BUG_ON(!list_empty(&fence->cb_list));
> +
> +       if (fence->ops->release)
> +               fence->ops->release(fence);
> +       else
> +               kfree(fence);
> +}
> +EXPORT_SYMBOL(release_fence);
> +
> +/**
> + * fence_enable_sw_signaling - enable signaling on fence
> + * @fence:     [in]    the fence to enable
> + *
> + * this will request for sw signaling to be enabled, to make the fence
> + * complete as soon as possible
> + */
> +void fence_enable_sw_signaling(struct fence *fence)
> +{
> +       unsigned long flags;
> +
> +       if (!test_and_set_bit(FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags) &&
> +           !test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> +               trace_fence_enable_signal(fence);
> +
> +               spin_lock_irqsave(fence->lock, flags);
> +
> +               if (!fence->ops->enable_signaling(fence))
> +                       __fence_signal(fence);
> +
> +               spin_unlock_irqrestore(fence->lock, flags);
> +       }
> +}
> +EXPORT_SYMBOL(fence_enable_sw_signaling);
> +
> +/**
> + * 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
> + *
> + * cb will be initialized by 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)
> + *
> + * Add a software callback to the fence. Same restrictions apply to
> + * refcount as it does to 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 fence_signal. The callback itself can be called
> + * from irq context.
> + *
> + */
> +int fence_add_callback(struct fence *fence, struct fence_cb *cb,
> +                      fence_func_t func)
> +{
> +       unsigned long flags;
> +       int ret = 0;
> +       bool was_set;
> +
> +       if (WARN_ON(!fence || !func))
> +               return -EINVAL;
> +
> +       if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> +               INIT_LIST_HEAD(&cb->node);
> +               return -ENOENT;
> +       }
> +
> +       spin_lock_irqsave(fence->lock, flags);
> +
> +       was_set = test_and_set_bit(FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags);
> +
> +       if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +               ret = -ENOENT;
> +       else if (!was_set) {
> +               trace_fence_enable_signal(fence);
> +
> +               if (!fence->ops->enable_signaling(fence)) {
> +                       __fence_signal(fence);
> +                       ret = -ENOENT;
> +               }
> +       }
> +
> +       if (!ret) {
> +               cb->func = func;
> +               list_add_tail(&cb->node, &fence->cb_list);
> +       } else
> +               INIT_LIST_HEAD(&cb->node);
> +       spin_unlock_irqrestore(fence->lock, flags);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL(fence_add_callback);
> +
> +/**
> + * fence_remove_callback - remove a callback from the signaling list
> + * @fence:     [in]    the fence to wait on
> + * @cb:                [in]    the callback to remove
> + *
> + * Remove a previously queued callback from the fence. This function returns
> + * true if the callback is succesfully removed, or false if the fence has
> + * already been signaled.
> + *
> + * *WARNING*:
> + * Cancelling a callback should only be done if you really know what you're
> + * 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.
> + */
> +bool
> +fence_remove_callback(struct fence *fence, struct fence_cb *cb)
> +{
> +       unsigned long flags;
> +       bool ret;
> +
> +       spin_lock_irqsave(fence->lock, flags);
> +
> +       ret = !list_empty(&cb->node);
> +       if (ret)
> +               list_del_init(&cb->node);
> +
> +       spin_unlock_irqrestore(fence->lock, flags);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL(fence_remove_callback);
> +
> +struct default_wait_cb {
> +       struct fence_cb base;
> +       struct task_struct *task;
> +};
> +
> +static void
> +fence_default_wait_cb(struct fence *fence, struct fence_cb *cb)
> +{
> +       struct default_wait_cb *wait =
> +               container_of(cb, struct default_wait_cb, base);
> +
> +       wake_up_state(wait->task, TASK_NORMAL);
> +}
> +
> +/**
> + * 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
> + *
> + * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
> + * remaining timeout in jiffies on success.
> + */
> +long
> +fence_default_wait(struct fence *fence, bool intr, signed long timeout)
> +{
> +       struct default_wait_cb cb;
> +       unsigned long flags;
> +       long ret = timeout;
> +       bool was_set;
> +
> +       if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +               return timeout;
> +
> +       spin_lock_irqsave(fence->lock, flags);
> +
> +       if (intr && signal_pending(current)) {
> +               ret = -ERESTARTSYS;
> +               goto out;
> +       }
> +
> +       was_set = test_and_set_bit(FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags);
> +
> +       if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +               goto out;
> +
> +       if (!was_set) {
> +               trace_fence_enable_signal(fence);
> +
> +               if (!fence->ops->enable_signaling(fence)) {
> +                       __fence_signal(fence);
> +                       goto out;
> +               }
> +       }
> +
> +       cb.base.func = fence_default_wait_cb;
> +       cb.task = current;
> +       list_add(&cb.base.node, &fence->cb_list);
> +
> +       while (!test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags) && ret > 0) {
> +               if (intr)
> +                       __set_current_state(TASK_INTERRUPTIBLE);
> +               else
> +                       __set_current_state(TASK_UNINTERRUPTIBLE);
> +               spin_unlock_irqrestore(fence->lock, flags);
> +
> +               ret = schedule_timeout(ret);
> +
> +               spin_lock_irqsave(fence->lock, flags);
> +               if (ret > 0 && intr && signal_pending(current))
> +                       ret = -ERESTARTSYS;
> +       }
> +
> +       if (!list_empty(&cb.base.node))
> +               list_del(&cb.base.node);
> +       __set_current_state(TASK_RUNNING);
> +
> +out:
> +       spin_unlock_irqrestore(fence->lock, flags);
> +       return ret;
> +}
> +EXPORT_SYMBOL(fence_default_wait);
> +
> +/**
> + * __fence_init - Initialize a custom fence.
> + * @fence:     [in]    the fence to initialize
> + * @ops:       [in]    the 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
> + *
> + * 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 fence_ops.enable_signaling gets called. This can
> + * be used for other implementing other types of fence.
> + *
> + * context and seqno are used for easy comparison between fences, allowing
> + * to check which fence is later by simply using fence_later.
> + */
> +void
> +__fence_init(struct fence *fence, const struct fence_ops *ops,
> +            spinlock_t *lock, unsigned context, unsigned seqno)
> +{
> +       BUG_ON(!lock);
> +       BUG_ON(!ops || !ops->wait || !ops->enable_signaling || !ops->get_driver_name || !ops->get_timeline_name);
> +
> +       kref_init(&fence->refcount);
> +       fence->ops = ops;
> +       INIT_LIST_HEAD(&fence->cb_list);
> +       fence->lock = lock;
> +       fence->context = context;
> +       fence->seqno = seqno;
> +       fence->flags = 0UL;
> +
> +       trace_fence_init(fence);
> +}
> +EXPORT_SYMBOL(__fence_init);
> diff --git a/include/linux/fence.h b/include/linux/fence.h
> new file mode 100644
> index 000000000000..a868eceb7cf5
> --- /dev/null
> +++ b/include/linux/fence.h
> @@ -0,0 +1,329 @@
> +/*
> + * Fence mechanism for dma-buf to allow for asynchronous dma access
> + *
> + * Copyright (C) 2012 Canonical Ltd
> + * Copyright (C) 2012 Texas Instruments
> + *
> + * Authors:
> + * Rob Clark <robdclark@xxxxxxxxx>
> + * Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef __LINUX_FENCE_H
> +#define __LINUX_FENCE_H
> +
> +#include <linux/err.h>
> +#include <linux/wait.h>
> +#include <linux/list.h>
> +#include <linux/bitops.h>
> +#include <linux/kref.h>
> +#include <linux/sched.h>
> +#include <linux/printk.h>
> +
> +struct fence;
> +struct fence_ops;
> +struct fence_cb;
> +
> +/**
> + * struct fence - software synchronization primitive
> + * @refcount: refcount for this fence
> + * @ops: fence_ops associated with this fence
> + * @cb_list: list of all callbacks to call
> + * @lock: spin_lock_irqsave used for locking
> + * @context: execution context this fence belongs to, returned by
> + *           fence_context_alloc()
> + * @seqno: the sequence number of this fence inside the execution context,
> + * can be compared to decide which fence would be signaled later.
> + * @flags: A mask of FENCE_FLAG_* defined below
> + * @timestamp: Timestamp when the fence was signaled.
> + * @status: Optional, only valid if < 0, must be set before calling
> + * fence_signal, indicates that the fence has completed with an error.
> + *
> + * the flags member must be manipulated and read using the appropriate
> + * atomic ops (bit_*), so taking the spinlock will not be needed most
> + * of the time.
> + *
> + * FENCE_FLAG_SIGNALED_BIT - fence is already signaled
> + * FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called*
> + * FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
> + * implementer of the fence for its own purposes. Can be used in different
> + * ways by different fence implementers, so do not rely on this.
> + *
> + * *) Since atomic bitops are used, this is not guaranteed to be the case.
> + * Particularly, if the bit was set, but fence_signal was called right
> + * before this bit was set, it would have been able to set the
> + * FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
> + * Adding a check for FENCE_FLAG_SIGNALED_BIT after setting
> + * FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
> + * after fence_signal was called, any enable_signaling call will have either
> + * been completed, or never called at all.
> + */
> +struct fence {
> +       struct kref refcount;
> +       const struct fence_ops *ops;
> +       struct list_head cb_list;
> +       spinlock_t *lock;
> +       unsigned context, seqno;
> +       unsigned long flags;
> +       ktime_t timestamp;
> +       int status;
> +};
> +
> +enum fence_flag_bits {
> +       FENCE_FLAG_SIGNALED_BIT,
> +       FENCE_FLAG_ENABLE_SIGNAL_BIT,
> +       FENCE_FLAG_USER_BITS, /* must always be last member */
> +};
> +
> +typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb);
> +
> +/**
> + * struct fence_cb - callback for fence_add_callback
> + * @node: used by fence_add_callback to append this struct to fence::cb_list
> + * @func: fence_func_t to call
> + *
> + * This struct will be initialized by fence_add_callback, additional
> + * data can be passed along by embedding fence_cb in another struct.
> + */
> +struct fence_cb {
> +       struct list_head node;
> +       fence_func_t func;
> +};
> +
> +/**
> + * struct fence_ops - operations implemented for fence
> + * @get_driver_name: returns the driver name.
> + * @get_timeline_name: return the name of the context this fence belongs to.
> + * @enable_signaling: enable software signaling of fence.
> + * @signaled: [optional] peek whether the fence is signaled, can be null.
> + * @wait: custom wait implementation, or fence_default_wait.
> + * @release: [optional] called on destruction of fence, can be null
> + * @fill_driver_data: [optional] callback to fill in free-form debug info
> + * Returns amount of bytes filled, or -errno.
> + * @fence_value_str: [optional] fills in the value of the fence as a string
> + * @timeline_value_str: [optional] fills in the current value of the timeline as a string
> + *
> + * Notes on enable_signaling:
> + * For fence implementations that have the capability for hw->hw
> + * signaling, they can implement this op to enable the necessary
> + * irqs, or insert commands into cmdstream, etc.  This is called
> + * in the first wait() or add_callback() path to let the fence
> + * implementation know that there is another driver waiting on
> + * the signal (ie. hw->sw case).
> + *
> + * This function can be called called from atomic context, but not
> + * from irq context, so normal spinlocks can be used.
> + *
> + * A return value of false indicates the fence already passed,
> + * or some failure occured that made it impossible to enable
> + * signaling. True indicates succesful enabling.
> + *
> + * fence->status may be set in enable_signaling, but only when false is returned.
> + *
> + * Calling fence_signal before enable_signaling is called allows
> + * for a tiny race window in which enable_signaling is called during,
> + * before, or after fence_signal. To fight this, it is recommended
> + * that before enable_signaling returns true an extra reference is
> + * taken on the fence, to be released when the fence is signaled.
> + * This will mean fence_signal will still be called twice, but
> + * the second time will be a noop since it was already signaled.
> + *
> + * Notes on signaled:
> + * May set fence->status if returning true.
> + *
> + * Notes on wait:
> + * Must not be NULL, set to fence_default_wait for default implementation.
> + * the fence_default_wait implementation should work for any fence, as long
> + * as enable_signaling works correctly.
> + *
> + * Must return -ERESTARTSYS if the wait is intr = true and the wait was
> + * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
> + * timed out. Can also return other error values on custom implementations,
> + * which should be treated as if the fence is signaled. For example a hardware
> + * lockup could be reported like that.
> + *
> + * Notes on release:
> + * Can be NULL, this function allows additional commands to run on
> + * destruction of the fence. Can be called from irq context.
> + * If pointer is set to NULL, kfree will get called instead.
> + */
> +
> +struct fence_ops {
> +       const char *(*get_driver_name)(struct fence *fence);
> +       const char *(*get_timeline_name)(struct fence *fence);
> +       bool (*enable_signaling)(struct fence *fence);
> +       bool (*signaled)(struct fence *fence);
> +       long (*wait)(struct fence *fence, bool intr, signed long timeout);
> +       void (*release)(struct fence *fence);
> +
> +       int (*fill_driver_data)(struct fence *fence, void *data, int size);
> +       void (*fence_value_str)(struct fence *fence, char *str, int size);
> +       void (*timeline_value_str)(struct fence *fence, char *str, int size);
> +};
> +
> +void __fence_init(struct fence *fence, const struct fence_ops *ops,
> +                 spinlock_t *lock, unsigned context, unsigned seqno);
> +
> +/**
> + * fence_get - increases refcount of the fence
> + * @fence:     [in]    fence to increase refcount of
> + */
> +static inline void fence_get(struct fence *fence)
> +{
> +       if (WARN_ON(!fence))
> +               return;
> +       kref_get(&fence->refcount);
> +}
> +
> +extern void release_fence(struct kref *kref);
> +
> +/**
> + * fence_put - decreases refcount of the fence
> + * @fence:     [in]    fence to reduce refcount of
> + */
> +static inline void fence_put(struct fence *fence)
> +{
> +       if (WARN_ON(!fence))
> +               return;
> +       kref_put(&fence->refcount, release_fence);
> +}
> +
> +int fence_signal(struct fence *fence);
> +int __fence_signal(struct fence *fence);
> +long fence_default_wait(struct fence *fence, bool intr, signed long timeout);
> +int fence_add_callback(struct fence *fence, struct fence_cb *cb,
> +                      fence_func_t func);
> +bool fence_remove_callback(struct fence *fence, struct fence_cb *cb);
> +void fence_enable_sw_signaling(struct fence *fence);
> +
> +static inline bool
> +__fence_is_signaled(struct fence *fence)
> +{
> +       if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +               return true;
> +
> +       if (fence->ops->signaled && fence->ops->signaled(fence)) {
> +               __fence_signal(fence);
> +               return true;
> +       }
> +
> +       return false;
> +}
> +
> +/**
> + * fence_is_signaled - Return an indication if the fence is signaled yet.
> + * @fence:     [in]    the fence to check
> + *
> + * Returns true if the fence was already signaled, false if not. Since this
> + * function doesn't enable signaling, it is not guaranteed to ever return true
> + * If fence_add_callback, fence_wait or fence_enable_sw_signaling
> + * haven't been called before.
> + *
> + * It's recommended for seqno fences to call fence_signal when the
> + * operation is complete, it makes it possible to prevent issues from
> + * wraparound between time of issue and time of use by checking the return
> + * value of this function before calling hardware-specific wait instructions.
> + */
> +static inline bool
> +fence_is_signaled(struct fence *fence)
> +{
> +       if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +               return true;
> +
> +       if (fence->ops->signaled && fence->ops->signaled(fence)) {
> +               fence_signal(fence);
> +               return true;
> +       }
> +
> +       return false;
> +}
> +
> +/**
> + * fence_later - return the chronologically later fence
> + * @f1:        [in]    the first fence from the same context
> + * @f2:        [in]    the second fence from the same context
> + *
> + * Returns NULL if both fences are signaled, otherwise the fence that would be
> + * signaled last. Both fences must be from the same context, since a seqno is
> + * not re-used across contexts.
> + */
> +static inline struct fence *fence_later(struct fence *f1, struct fence *f2)
> +{
> +       BUG_ON(f1->context != f2->context);
> +
> +       /*
> +        * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been
> +        * set called if enable_signaling wasn't, and enabling that here is
> +        * overkill.
> +        */
> +       if (f2->seqno - f1->seqno <= INT_MAX)
> +               return fence_is_signaled(f2) ? NULL : f2;
> +       else
> +               return fence_is_signaled(f1) ? NULL : f1;
> +}
> +
> +long fence_wait_timeout(struct fence *fence, bool intr, signed long timeout);
> +
> +
> +/**
> + * fence_wait - sleep until the fence gets signaled
> + * @fence:     [in]    the fence to wait on
> + * @intr:      [in]    if true, do an interruptible wait
> + *
> + * This function will return -ERESTARTSYS if interrupted by a signal,
> + * or 0 if the fence was signaled. Other error values may be
> + * returned on custom implementations.
> + *
> + * Performs a synchronous wait on this fence. It is assumed the caller
> + * 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.
> + */
> +static inline long fence_wait(struct fence *fence, bool intr)
> +{
> +       long ret;
> +
> +       /* Since fence_wait_timeout cannot timeout with
> +        * MAX_SCHEDULE_TIMEOUT, only valid return values are
> +        * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
> +        */
> +       ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
> +
> +       return ret < 0 ? ret : 0;
> +}
> +
> +unsigned fence_context_alloc(unsigned num);
> +
> +#define FENCE_TRACE(f, fmt, args...) \
> +       do {                                                                    \
> +               struct fence *__ff = (f);                                       \
> +               if (config_enabled(CONFIG_FENCE_TRACE))                 \
> +                       pr_info("f %u#%u: " fmt,                                \
> +                               __ff->context, __ff->seqno, ##args);            \
> +       } while (0)
> +
> +#define FENCE_WARN(f, fmt, args...) \
> +       do {                                                                    \
> +               struct fence *__ff = (f);                                       \
> +               pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno, ##args);   \
> +       } while (0)
> +
> +#define FENCE_ERR(f, fmt, args...) \
> +       do {                                                                    \
> +               struct fence *__ff = (f);                                       \
> +               pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno, ##args);    \
> +       } while (0)
> +
> +#endif /* __LINUX_FENCE_H */
> diff --git a/include/trace/events/fence.h b/include/trace/events/fence.h
> new file mode 100644
> index 000000000000..ce3d83230cff
> --- /dev/null
> +++ b/include/trace/events/fence.h
> @@ -0,0 +1,125 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM fence
> +
> +#if !defined(_TRACE_FENCE_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_FENCE_H
> +
> +#include <linux/tracepoint.h>
> +
> +struct fence;
> +
> +TRACE_EVENT(fence_annotate_wait_on,
> +
> +       /* fence: the fence waiting on f1, f1: the fence to be waited on. */
> +       TP_PROTO(struct fence *fence, struct fence *f1),
> +
> +       TP_ARGS(fence, f1),
> +
> +       TP_STRUCT__entry(
> +               __string(driver, fence->ops->get_driver_name(fence))
> +               __string(timeline, fence->ops->get_driver_name(fence))
> +               __field(unsigned int, context)
> +               __field(unsigned int, seqno)
> +
> +               __string(waiting_driver, f1->ops->get_driver_name(f1))
> +               __string(waiting_timeline, f1->ops->get_timeline_name(f1))
> +               __field(unsigned int, waiting_context)
> +               __field(unsigned int, waiting_seqno)
> +       ),
> +
> +       TP_fast_assign(
> +               __assign_str(driver, fence->ops->get_driver_name(fence))
> +               __assign_str(timeline, fence->ops->get_timeline_name(fence))
> +               __entry->context = fence->context;
> +               __entry->seqno = fence->seqno;
> +
> +               __assign_str(waiting_driver, f1->ops->get_driver_name(f1))
> +               __assign_str(waiting_timeline, f1->ops->get_timeline_name(f1))
> +               __entry->waiting_context = f1->context;
> +               __entry->waiting_seqno = f1->seqno;
> +
> +       ),
> +
> +       TP_printk("driver=%s timeline=%s context=%u seqno=%u "
> +                 "waits on driver=%s timeline=%s context=%u seqno=%u",
> +                 __get_str(driver), __get_str(timeline), __entry->context, __entry->seqno,
> +                 __get_str(waiting_driver), __get_str(waiting_timeline), __entry->waiting_context, __entry->waiting_seqno)
> +);
> +
> +DECLARE_EVENT_CLASS(fence,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence),
> +
> +       TP_STRUCT__entry(
> +               __string(driver, fence->ops->get_driver_name(fence))
> +               __string(timeline, fence->ops->get_timeline_name(fence))
> +               __field(unsigned int, context)
> +               __field(unsigned int, seqno)
> +       ),
> +
> +       TP_fast_assign(
> +               __assign_str(driver, fence->ops->get_driver_name(fence))
> +               __assign_str(timeline, fence->ops->get_timeline_name(fence))
> +               __entry->context = fence->context;
> +               __entry->seqno = fence->seqno;
> +       ),
> +
> +       TP_printk("driver=%s timeline=%s context=%u seqno=%u",
> +                 __get_str(driver), __get_str(timeline), __entry->context, __entry->seqno)
> +);
> +
> +DEFINE_EVENT(fence, fence_emit,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence)
> +);
> +
> +DEFINE_EVENT(fence, fence_init,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence)
> +);
> +
> +DEFINE_EVENT(fence, fence_destroy,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence)
> +);
> +
> +DEFINE_EVENT(fence, fence_enable_signal,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence)
> +);
> +
> +DEFINE_EVENT(fence, fence_signaled,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence)
> +);
> +
> +DEFINE_EVENT(fence, fence_wait_start,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence)
> +);
> +
> +DEFINE_EVENT(fence, fence_wait_end,
> +
> +       TP_PROTO(struct fence *fence),
> +
> +       TP_ARGS(fence)
> +);
> +
> +#endif /*  _TRACE_FENCE_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
>
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