Re: [PATCH 2/4] drm/i915: Consolidate get_fence with pin_fence

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On 03/07/2017 11:14, Chris Wilson wrote:
Following the pattern now used for obj->mm.pages, use just pin_fence and
unpin_fence to control access to the fence registers. I.e. instead of
calling get_fence(); pin_fence(), we now just need to call pin_fence().
This will make it easier to reduce the locking requirements around
fence registers.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/i915_drv.h            |  4 ----
  drivers/gpu/drm/i915/i915_gem.c            |  3 ++-
  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 10 +++++-----
  drivers/gpu/drm/i915/i915_gem_fence_reg.c  | 27 ++++++++++++++++++++++-----
  drivers/gpu/drm/i915/i915_vma.c            |  3 +--
  drivers/gpu/drm/i915/i915_vma.h            | 20 ++++++++------------
  drivers/gpu/drm/i915/intel_display.c       |  3 +--
  7 files changed, 39 insertions(+), 31 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 0029bb949e90..b08b56a2e680 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3545,10 +3545,6 @@ i915_vm_to_ppgtt(struct i915_address_space *vm)
  	return container_of(vm, struct i915_hw_ppgtt, base);
  }
-/* i915_gem_fence_reg.c */
-int __must_check i915_vma_get_fence(struct i915_vma *vma);
-int __must_check i915_vma_put_fence(struct i915_vma *vma);
-
  void i915_gem_revoke_fences(struct drm_i915_private *dev_priv);
  void i915_gem_restore_fences(struct drm_i915_private *dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 1b2dfa8bdeef..939a299260e9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1941,7 +1941,7 @@ int i915_gem_fault(struct vm_fault *vmf)
  	if (ret)
  		goto err_unpin;
- ret = i915_vma_get_fence(vma);
+	ret = i915_vma_pin_fence(vma);

Hm, I think fence stealing stops working with this change?

Regards,

Tvrtko

  	if (ret)
  		goto err_unpin;
@@ -1957,6 +1957,7 @@ int i915_gem_fault(struct vm_fault *vmf)
  			       min_t(u64, vma->size, area->vm_end - area->vm_start),
  			       &ggtt->mappable);
+ i915_vma_unpin_fence(vma);
  err_unpin:
  	__i915_vma_unpin(vma);
  err_unlock:
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 929f275e67aa..22a9f5358322 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -365,12 +365,12 @@ eb_pin_vma(struct i915_execbuffer *eb,
  		return;
if (unlikely(entry->flags & EXEC_OBJECT_NEEDS_FENCE)) {
-		if (unlikely(i915_vma_get_fence(vma))) {
+		if (unlikely(i915_vma_pin_fence(vma))) {
  			i915_vma_unpin(vma);
  			return;
  		}
- if (i915_vma_pin_fence(vma))
+		if (vma->fence)
  			entry->flags |= __EXEC_OBJECT_HAS_FENCE;
  	}
@@ -384,7 +384,7 @@ __eb_unreserve_vma(struct i915_vma *vma,
  	GEM_BUG_ON(!(entry->flags & __EXEC_OBJECT_HAS_PIN));
if (unlikely(entry->flags & __EXEC_OBJECT_HAS_FENCE))
-		i915_vma_unpin_fence(vma);
+		__i915_vma_unpin_fence(vma);
__i915_vma_unpin(vma);
  }
@@ -564,13 +564,13 @@ static int eb_reserve_vma(const struct i915_execbuffer *eb,
  	GEM_BUG_ON(eb_vma_misplaced(entry, vma));
if (unlikely(entry->flags & EXEC_OBJECT_NEEDS_FENCE)) {
-		err = i915_vma_get_fence(vma);
+		err = i915_vma_pin_fence(vma);
  		if (unlikely(err)) {
  			i915_vma_unpin(vma);
  			return err;
  		}
- if (i915_vma_pin_fence(vma))
+		if (vma->fence)
  			entry->flags |= __EXEC_OBJECT_HAS_FENCE;
  	}
diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.c b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
index 5fe2cd8c8f28..55ac7bc14fce 100644
--- a/drivers/gpu/drm/i915/i915_gem_fence_reg.c
+++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
@@ -280,8 +280,7 @@ static int fence_update(struct drm_i915_fence_reg *fence,
   *
   * 0 on success, negative error code on failure.
   */
-int
-i915_vma_put_fence(struct i915_vma *vma)
+int i915_vma_put_fence(struct i915_vma *vma)
  {
  	struct drm_i915_fence_reg *fence = vma->fence;
@@ -299,6 +298,8 @@ static struct drm_i915_fence_reg *fence_find(struct drm_i915_private *dev_priv)
  	struct drm_i915_fence_reg *fence;
list_for_each_entry(fence, &dev_priv->mm.fence_list, link) {
+		GEM_BUG_ON(fence->vma && fence->vma->fence != fence);
+
  		if (fence->pin_count)
  			continue;
@@ -313,7 +314,7 @@ static struct drm_i915_fence_reg *fence_find(struct drm_i915_private *dev_priv)
  }
/**
- * i915_vma_get_fence - set up fencing for a vma
+ * i915_vma_pin_fence - set up fencing for a vma
   * @vma: vma to map through a fence reg
   *
   * When mapping objects through the GTT, userspace wants to be able to write
@@ -331,10 +332,11 @@ static struct drm_i915_fence_reg *fence_find(struct drm_i915_private *dev_priv)
   * 0 on success, negative error code on failure.
   */
  int
-i915_vma_get_fence(struct i915_vma *vma)
+i915_vma_pin_fence(struct i915_vma *vma)
  {
  	struct drm_i915_fence_reg *fence;
  	struct i915_vma *set = i915_gem_object_is_tiled(vma->obj) ? vma : NULL;
+	int err;
/* Note that we revoke fences on runtime suspend. Therefore the user
  	 * must keep the device awake whilst using the fence.
@@ -344,6 +346,8 @@ i915_vma_get_fence(struct i915_vma *vma)
  	/* Just update our place in the LRU if our fence is getting reused. */
  	if (vma->fence) {
  		fence = vma->fence;
+		GEM_BUG_ON(fence->vma != vma);
+		fence->pin_count++;
  		if (!fence->dirty) {
  			list_move_tail(&fence->link,
  				       &fence->i915->mm.fence_list);
@@ -353,10 +357,19 @@ i915_vma_get_fence(struct i915_vma *vma)
  		fence = fence_find(vma->vm->i915);
  		if (IS_ERR(fence))
  			return PTR_ERR(fence);
+		fence->pin_count++;
  	} else
  		return 0;
- return fence_update(fence, set);
+	err = fence_update(fence, set);
+	if (err)
+		goto err_unpin;
+
+	return 0;
+
+err_unpin:
+	fence->pin_count--;
+	return err;
  }
/**
@@ -378,6 +391,8 @@ void i915_gem_revoke_fences(struct drm_i915_private *dev_priv)
  	for (i = 0; i < dev_priv->num_fence_regs; i++) {
  		struct drm_i915_fence_reg *fence = &dev_priv->fence_regs[i];
+ GEM_BUG_ON(fence->vma && fence->vma->fence != fence);
+
  		if (fence->vma)
  			i915_gem_release_mmap(fence->vma->obj);
  	}
@@ -399,6 +414,8 @@ void i915_gem_restore_fences(struct drm_i915_private *dev_priv)
  		struct drm_i915_fence_reg *reg = &dev_priv->fence_regs[i];
  		struct i915_vma *vma = reg->vma;
+ GEM_BUG_ON(vma && vma->fence != reg);
+
  		/*
  		 * Commit delayed tiling changes if we have an object still
  		 * attached to the fence, otherwise just clear the fence.
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index d7330d3eeab6..efbfee8eac99 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -303,12 +303,11 @@ void __iomem *i915_vma_pin_iomap(struct i915_vma *vma)
__i915_vma_pin(vma); - ret = i915_vma_get_fence(vma);
+	ret = i915_vma_pin_fence(vma);
  	if (ret) {
  		__i915_vma_unpin(vma);
  		return IO_ERR_PTR(ret);
  	}
-	i915_vma_pin_fence(vma);
return ptr;
  }
diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
index 15e86e50a825..19f58af4f1bf 100644
--- a/drivers/gpu/drm/i915/i915_vma.h
+++ b/drivers/gpu/drm/i915/i915_vma.h
@@ -342,15 +342,13 @@ static inline struct page *i915_vma_first_page(struct i915_vma *vma)
   *
   * True if the vma has a fence, false otherwise.
   */
-static inline bool
-i915_vma_pin_fence(struct i915_vma *vma)
+int i915_vma_pin_fence(struct i915_vma *vma);
+int __must_check i915_vma_put_fence(struct i915_vma *vma);
+
+static inline void __i915_vma_unpin_fence(struct i915_vma *vma)
  {
-	lockdep_assert_held(&vma->obj->base.dev->struct_mutex);
-	if (vma->fence) {
-		vma->fence->pin_count++;
-		return true;
-	} else
-		return false;
+	GEM_BUG_ON(vma->fence->pin_count <= 0);
+	vma->fence->pin_count--;
  }
/**
@@ -365,10 +363,8 @@ static inline void
  i915_vma_unpin_fence(struct i915_vma *vma)
  {
  	lockdep_assert_held(&vma->obj->base.dev->struct_mutex);
-	if (vma->fence) {
-		GEM_BUG_ON(vma->fence->pin_count <= 0);
-		vma->fence->pin_count--;
-	}
+	if (vma->fence)
+		__i915_vma_unpin_fence(vma);
  }
#endif
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 4e03ca6c946f..432bbaf460b4 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2183,8 +2183,7 @@ intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb, unsigned int rotation)
  		 * something and try to run the system in a "less than optimal"
  		 * mode that matches the user configuration.
  		 */
-		if (i915_vma_get_fence(vma) == 0)
-			i915_vma_pin_fence(vma);
+		i915_vma_pin_fence(vma);
  	}
i915_vma_get(vma);

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