linux-kernel - [RFC 1/3] dma-fence: Add boost fence op

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Date:   Wed, 19 May 2021 11:38:52 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        linux-media@...r.kernel.org (open list:DMA BUFFER SHARING FRAMEWORK),
        linaro-mm-sig@...ts.linaro.org (moderated list:DMA BUFFER SHARING
        FRAMEWORK), linux-kernel@...r.kernel.org (open list)
Subject: [RFC 1/3] dma-fence: Add boost fence op

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

Add a way to hint to the fence signaler that a fence waiter has missed a
deadline waiting on the fence.

In some cases, missing a vblank can result in lower gpu utilization,
when really we want to go in the opposite direction and boost gpu freq.
The boost callback gives some feedback to the fence signaler that we
are missing deadlines, so it can take this into account in it's freq/
utilization calculations.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 include/linux/dma-fence.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 9f12efaaa93a..172702521acc 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -231,6 +231,17 @@ struct dma_fence_ops {
 	signed long (*wait)(struct dma_fence *fence,
 			    bool intr, signed long timeout);
 
+	/**
+	 * @boost:
+	 *
+	 * Optional callback, to indicate that a fence waiter missed a deadline.
+	 * This can serve as a signal that (if possible) whatever signals the
+	 * fence should boost it's clocks.
+	 *
+	 * This can be called in any context that can call dma_fence_wait().
+	 */
+	void (*boost)(struct dma_fence *fence);
+
 	/**
 	 * @release:
 	 *
@@ -586,6 +597,21 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
 	return ret < 0 ? ret : 0;
 }
 
+/**
+ * dma_fence_boost - hint from waiter that it missed a deadline
+ *
+ * @fence: the fence that caused the missed deadline
+ *
+ * This function gives a hint from a fence waiter that a deadline was
+ * missed, so that the fence signaler can factor this in to device
+ * power state decisions
+ */
+static inline void dma_fence_boost(struct dma_fence *fence)
+{
+	if (fence->ops->boost)
+		fence->ops->boost(fence);
+}
+
 struct dma_fence *dma_fence_get_stub(void);
 u64 dma_fence_context_alloc(unsigned num);
 
-- 
2.30.2