[PATCH 2/4] drm/i915: fixup seqno allocation logic for lazy_request

[Daniel Vetter <daniel.vetter@ffwll.ch>]

Currently we reserve seqnos only when we emit the request to the ring
(by bumping dev_priv->next_seqno), but start using it much earlier for
ring->oustanding_lazy_request. When 2 threads compete for the gpu and
run on two different rings (e.g. ddx on blitter vs. compositor)
hilarity ensued, especially when we get constantly interrupted while
reserving buffers.

Breakage seems to have been introduced in

commit 6f392d548658a17600da7faaf8a5df25ee5f01f6
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Sat Aug 7 11:01:22 2010 +0100

    drm/i915: Use a common seqno for all rings.

This patch fixes up the seqno reservation logic by moving it into
i915_gem_next_request_seqno. The ring->add_request functions now
superflously still return the new seqno through a pointer, that will
be refactored in the next patch.

v2: Keep i915_gem_get_seqno (but move it to i915_gem.c) to make it
clear that we only have one seqno counter for all rings. Suggested by
Chris Wilson.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45181
Tested-by: Nicolas Kalkhof nkalkhof()at()web.de
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_drv.h         |    7 +------
 drivers/gpu/drm/i915/i915_gem.c         |   23 +++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_ringbuffer.c |   24 ++++--------------------
 3 files changed, 28 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 32737a3..2f102ad 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1159,12 +1159,7 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
 	return (int32_t)(seq1 - seq2) >= 0;
 }
 
-static inline u32
-i915_gem_next_request_seqno(struct intel_ring_buffer *ring)
-{
-	drm_i915_private_t *dev_priv = ring->dev->dev_private;
-	return ring->outstanding_lazy_request = dev_priv->next_seqno;
-}
+u32 i915_gem_next_request_seqno(struct intel_ring_buffer *ring);
 
 int __must_check i915_gem_object_get_fence(struct drm_i915_gem_object *obj,
 					   struct intel_ring_buffer *pipelined);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8f01c3d..dc8e45f 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1647,6 +1647,28 @@ i915_gem_process_flushing_list(struct intel_ring_buffer *ring,
 	}
 }
 
+static u32
+i915_gem_get_seqno(struct drm_device *dev)
+{
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	u32 seqno = dev_priv->next_seqno;
+
+	/* reserve 0 for non-seqno */
+	if (++dev_priv->next_seqno == 0)
+		dev_priv->next_seqno = 1;
+
+	return seqno;
+}
+
+u32
+i915_gem_next_request_seqno(struct intel_ring_buffer *ring)
+{
+	if (ring->outstanding_lazy_request == 0)
+		ring->outstanding_lazy_request = i915_gem_get_seqno(ring->dev);
+
+	return ring->outstanding_lazy_request;
+}
+
 int
 i915_add_request(struct intel_ring_buffer *ring,
 		 struct drm_file *file,
@@ -1658,6 +1680,7 @@ i915_add_request(struct intel_ring_buffer *ring,
 	int ret;
 
 	BUG_ON(request == NULL);
+	seqno = i915_gem_next_request_seqno(ring);
 
 	ret = ring->add_request(ring, &seqno);
 	if (ret)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 1ab842c..bc0d791 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -52,20 +52,6 @@ static inline int ring_space(struct intel_ring_buffer *ring)
 	return space;
 }
 
-static u32 i915_gem_get_seqno(struct drm_device *dev)
-{
-	drm_i915_private_t *dev_priv = dev->dev_private;
-	u32 seqno;
-
-	seqno = dev_priv->next_seqno;
-
-	/* reserve 0 for non-seqno */
-	if (++dev_priv->next_seqno == 0)
-		dev_priv->next_seqno = 1;
-
-	return seqno;
-}
-
 static int
 render_ring_flush(struct intel_ring_buffer *ring,
 		  u32	invalidate_domains,
@@ -467,7 +453,7 @@ gen6_add_request(struct intel_ring_buffer *ring,
 	mbox1_reg = ring->signal_mbox[0];
 	mbox2_reg = ring->signal_mbox[1];
 
-	*seqno = i915_gem_get_seqno(ring->dev);
+	*seqno = ring->outstanding_lazy_request;
 
 	update_mboxes(ring, *seqno, mbox1_reg);
 	update_mboxes(ring, *seqno, mbox2_reg);
@@ -565,8 +551,7 @@ static int
 pc_render_add_request(struct intel_ring_buffer *ring,
 		      u32 *result)
 {
-	struct drm_device *dev = ring->dev;
-	u32 seqno = i915_gem_get_seqno(dev);
+	u32 seqno = ring->outstanding_lazy_request;
 	struct pipe_control *pc = ring->private;
 	u32 scratch_addr = pc->gtt_offset + 128;
 	int ret;
@@ -617,8 +602,7 @@ static int
 render_ring_add_request(struct intel_ring_buffer *ring,
 			u32 *result)
 {
-	struct drm_device *dev = ring->dev;
-	u32 seqno = i915_gem_get_seqno(dev);
+	u32 seqno = ring->outstanding_lazy_request;
 	int ret;
 
 	ret = intel_ring_begin(ring, 4);
@@ -792,7 +776,7 @@ ring_add_request(struct intel_ring_buffer *ring,
 	if (ret)
 		return ret;
 
-	seqno = i915_gem_get_seqno(ring->dev);
+	seqno = ring->outstanding_lazy_request;
 
 	intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
 	intel_ring_emit(ring, I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
-- 
1.7.7.5