[PATCH] dma-fence: add get_signaled_timestamp to fence ops

[Veera Sundaram Sankaran]

Add an optional fence ops to allow drivers to be able to set the
timestamp for a fence. Some drivers have hardware capability to get
the precise timestamp of certain events based on which the fences
are triggered. This allows it to set accurate timestamp factoring
out any software and IRQ latencies. The get_signaled_timestamp ops,
if defined by the driver would be used during fence signaling to set
the timestamp, before setting the flag DMA_FENCE_FLAG_TIMESTAMP_BIT.
If the callback is not defined, ktime_get is used to set the fence
timestamp.

Signed-off-by: Veera Sundaram Sankaran <veeras at codeaurora.org>
---
 drivers/dma-buf/dma-fence.c |  6 +++++-
 include/linux/dma-fence.h   | 13 +++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 43624b4..95c6ab0 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -4,6 +4,7 @@
  *
  * Copyright (C) 2012 Canonical Ltd
  * Copyright (C) 2012 Texas Instruments
+ * Copyright (c) 2020 The Linux Foundation. All rights reserved.
  *
  * Authors:
  * Rob Clark <robdclark at gmail.com>
@@ -340,7 +341,10 @@ 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();
+	if (fence->ops->get_signaled_timestamp)
+		fence->timestamp = fence->ops->get_signaled_timestamp(fence);
+	else
+		fence->timestamp = ktime_get();
 	set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
 	trace_dma_fence_signaled(fence);
 
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 09e23ad..ce73aba 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -4,6 +4,7 @@
  *
  * Copyright (C) 2012 Canonical Ltd
  * Copyright (C) 2012 Texas Instruments
+ * Copyright (c) 2020 The Linux Foundation. All rights reserved.
  *
  * Authors:
  * Rob Clark <robdclark at gmail.com>
@@ -261,6 +262,18 @@ struct dma_fence_ops {
 	 */
 	void (*timeline_value_str)(struct dma_fence *fence,
 				   char *str, int size);
+
+	/**
+	 * @get_signaled_timestamp:
+	 *
+	 * Allows the driver to fill in precise timestamp for a fence.
+	 * This ops would be used during fence signalling to set the timestamp,
+	 * before setting the flag DMA_FENCE_FLAG_TIMESTAMP_BIT.
+	 *
+	 * This callback is optional. If this callback is not present,
+	 * ktime_get is used to fill in the timestamp.
+	 */
+	ktime_t (*get_signaled_timestamp)(struct dma_fence *fence);
 };
 
 void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
-- 
2.7.4