Some drivers have hardware capability to get the precise HW timestamp
of certain events based on which the fences are triggered. The delta
between the event HW timestamp & current HW reference timestamp can
be used to calculate the timestamp in kernel's CLOCK_MONOTONIC time
domain. This allows it to set accurate timestamp factoring out any
software and IRQ latencies. Add a timestamp variant of fence signal
function, dma_fence_signal_timestamp to allow drivers to update the
precise timestamp for fences.
Changes in v2:
- Add a new fence signal variant instead of modifying fence struct
Changes in v3:
- Add timestamp domain information to commit-text and
dma_fence_signal_timestamp documentation
Signed-off-by: Veera Sundaram Sankaran <veeras@xxxxxxxxxxxxxx>
---
drivers/dma-buf/dma-fence.c | 70 ++++++++++++++++++++++++++++++++++++++++-----
include/linux/dma-fence.h | 3 ++
2 files changed, 66 insertions(+), 7 deletions(-)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 7475e09..b83e9fa 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -312,22 +312,25 @@ void __dma_fence_might_wait(void)
/**
- * dma_fence_signal_locked - signal completion of a fence
+ * dma_fence_signal_timestamp_locked - signal completion of a fence
* @fence: the fence to signal
+ * @timestamp: fence signal timestamp in kernel's CLOCK_MONOTONIC time domain
*
* 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 the unsignaled to the signaled state and not back, it will
- * only be effective the first time.
+ * only be effective the first time. Set the timestamp provided as the fence
+ * signal timestamp.
*
- * Unlike dma_fence_signal(), this function must be called with &dma_fence.lock
- * held.
+ * Unlike dma_fence_signal_timestamp(), 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)
+int dma_fence_signal_timestamp_locked(struct dma_fence *fence,
+ ktime_t timestamp)
{
struct dma_fence_cb *cur, *tmp;
struct list_head cb_list;
@@ -341,7 +344,7 @@ int dma_fence_signal_locked(struct dma_fence *fence)
/* Stash the cb_list before replacing it with the timestamp */
list_replace(&fence->cb_list, &cb_list);
- fence->timestamp = ktime_get();
+ fence->timestamp = timestamp;
set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
trace_dma_fence_signaled(fence);
@@ -352,6 +355,59 @@ int dma_fence_signal_locked(struct dma_fence *fence)
return 0;
}
+EXPORT_SYMBOL(dma_fence_signal_timestamp_locked);
+
+/**
+ * dma_fence_signal_timestamp - signal completion of a fence
+ * @fence: the fence to signal
+ * @timestamp: fence signal timestamp in kernel's CLOCK_MONOTONIC time domain
+ *
+ * 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 the unsignaled to the signaled state and not back, it will
+ * only be effective the first time. Set the timestamp provided as the fence
+ * signal timestamp.
+ *
+ * Returns 0 on success and a negative error value when @fence has been
+ * signalled already.
+ */
+int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp)
+{
+ unsigned long flags;
+ int ret;
+
+ if (!fence)
+ return -EINVAL;
+
+ spin_lock_irqsave(fence->lock, flags);
+ ret = dma_fence_signal_timestamp_locked(fence, timestamp);
+ spin_unlock_irqrestore(fence->lock, flags);
+
+ return ret;
+}
+EXPORT_SYMBOL(dma_fence_signal_timestamp);
+
+/**
+ * dma_fence_signal_locked - signal completion of a fence
+ * @fence: the fence to signal
+ *
+ * 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 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.
+ *
+ * Returns 0 on success and a negative error value when @fence has been
+ * signalled already.
+ */
+int dma_fence_signal_locked(struct dma_fence *fence)
+{
+ return dma_fence_signal_timestamp_locked(fence, ktime_get());
+}
EXPORT_SYMBOL(dma_fence_signal_locked);
/**
@@ -379,7 +435,7 @@ int dma_fence_signal(struct dma_fence *fence)
tmp = dma_fence_begin_signalling();
spin_lock_irqsave(fence->lock, flags);
- ret = dma_fence_signal_locked(fence);
+ ret = dma_fence_signal_timestamp_locked(fence, ktime_get());
spin_unlock_irqrestore(fence->lock, flags);
dma_fence_end_signalling(tmp);
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 09e23ad..9f12efa 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -372,6 +372,9 @@ static inline void __dma_fence_might_wait(void) {}
int dma_fence_signal(struct dma_fence *fence);
int dma_fence_signal_locked(struct dma_fence *fence);
+int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
+int dma_fence_signal_timestamp_locked(struct dma_fence *fence,
+ ktime_t timestamp);
signed long dma_fence_default_wait(struct dma_fence *fence,
bool intr, signed long timeout);
int dma_fence_add_callback(struct dma_fence *fence,
--
2.7.4
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