linux-kernel - [RFC 1/4] dma-fence: Add deadline awareness

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Date:   Mon, 26 Jul 2021 16:38:48 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Matthew Brost <matthew.brost@...el.com>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
        Rob Clark <robdclark@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Christian König <christian.koenig@....com>,
        linux-media@...r.kernel.org (open list:SYNC FILE FRAMEWORK),
        linaro-mm-sig@...ts.linaro.org (moderated list:DMA BUFFER SHARING
        FRAMEWORK), linux-kernel@...r.kernel.org (open list)
Subject: [RFC 1/4] dma-fence: Add deadline awareness

From: Rob Clark <robdclark@...omium.org>

Add a way to hint to the fence signaler of an upcoming deadline, such as
vblank, which the fence waiter would prefer not to miss.  This is to aid
the fence signaler in making power management decisions, like boosting
frequency as the deadline approaches and awareness of missing deadlines
so that can be factored in to the frequency scaling.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/dma-buf/dma-fence.c | 39 +++++++++++++++++++++++++++++++++++++
 include/linux/dma-fence.h   | 17 ++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index ce0f5eff575d..2e0d25ab457e 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -910,6 +910,45 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count,
 }
 EXPORT_SYMBOL(dma_fence_wait_any_timeout);
 
+
+/**
+ * dma_fence_set_deadline - set desired fence-wait deadline
+ * @fence:    the fence that is to be waited on
+ * @deadline: the time by which the waiter hopes for the fence to be
+ *            signaled
+ *
+ * Inform the fence signaler of an upcoming deadline, such as vblank, by
+ * which point the waiter would prefer the fence to be signaled by.  This
+ * is intended to give feedback to the fence signaler to aid in power
+ * management decisions, such as boosting GPU frequency if a periodic
+ * vblank deadline is approaching.
+ */
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
+{
+	unsigned long flags;
+
+	if (dma_fence_is_signaled(fence))
+		return;
+
+	spin_lock_irqsave(fence->lock, flags);
+
+	/* If we already have an earlier deadline, keep it: */
+	if (test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &fence->flags) &&
+	    ktime_before(fence->deadline, deadline)) {
+		spin_unlock_irqrestore(fence->lock, flags);
+		return;
+	}
+
+	fence->deadline = deadline;
+	set_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &fence->flags);
+
+	spin_unlock_irqrestore(fence->lock, flags);
+
+	if (fence->ops->set_deadline)
+		fence->ops->set_deadline(fence, deadline);
+}
+EXPORT_SYMBOL(dma_fence_set_deadline);
+
 /**
  * dma_fence_init - Initialize a custom fence.
  * @fence: the fence to initialize
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 6ffb4b2c6371..4e6cfe4e6fbc 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -88,6 +88,7 @@ struct dma_fence {
 		/* @timestamp replaced by @rcu on dma_fence_release() */
 		struct rcu_head rcu;
 	};
+	ktime_t deadline;
 	u64 context;
 	u64 seqno;
 	unsigned long flags;
@@ -99,6 +100,7 @@ enum dma_fence_flag_bits {
 	DMA_FENCE_FLAG_SIGNALED_BIT,
 	DMA_FENCE_FLAG_TIMESTAMP_BIT,
 	DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
+	DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
 	DMA_FENCE_FLAG_USER_BITS, /* must always be last member */
 };
 
@@ -261,6 +263,19 @@ struct dma_fence_ops {
 	 */
 	void (*timeline_value_str)(struct dma_fence *fence,
 				   char *str, int size);
+
+	/**
+	 * @set_deadline:
+	 *
+	 * Callback to allow a fence waiter to inform the fence signaler of an
+	 * upcoming deadline, such as vblank, by which point the waiter would
+	 * prefer the fence to be signaled by.  This is intended to give feedback
+	 * to the fence signaler to aid in power management decisions, such as
+	 * boosting GPU frequency.
+	 *
+	 * This callback is optional.
+	 */
+	void (*set_deadline)(struct dma_fence *fence, ktime_t deadline);
 };
 
 void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
@@ -586,6 +601,8 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
 	return ret < 0 ? ret : 0;
 }
 
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
+
 struct dma_fence *dma_fence_get_stub(void);
 struct dma_fence *dma_fence_allocate_private_stub(void);
 u64 dma_fence_context_alloc(unsigned num);
-- 
2.31.1