drm/i915: Replace obj->pin_global with obj->frontbuffer

obj->pin_global was originally used as a means to keep the shrinker off
the active scanout, but we use the vma->pin_count itself for that and
the obj->frontbuffer to delay shrinking active framebuffers. The other
role that obj->pin_global gained was for spotting display objects inside
GEM and working harder to keep those coherent; for which we can again
simply inspect obj->frontbuffer directly.

Coming up next, we will want to manipulate the pin_global counter
outside of the principle locks, so would need to make pin_global atomic.
However, since obj->frontbuffer is already managed atomically, it makes
sense to use that the primary key for display objects instead of having
pin_global.

Ville pointed out the principle difference is that obj->frontbuffer is
set for as long as an intel_framebuffer is attached to an object, but
obj->pin_global was only raised for as long as the object was active. In
practice, this means that we consider the object as being on the scanout
for longer than is strictly required, causing us to be more proactive in
flushing -- though it should be true that we would have flushed
eventually when the back became the front, except that on the flip path
that flush is async but when hit from another ioctl it will be
synchronous.

v2: i915_gem_object_is_framebuffer()

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190902040303.14195-5-chris@chris-wilson.co.uk

1 files changed, 10 insertions, 24 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
index 9c58e8fac1d9..6af740a5e3db 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
@@ -27,7 +27,7 @@ static void __i915_gem_object_flush_for_display(struct drm_i915_gem_object *obj)
 
 void i915_gem_object_flush_if_display(struct drm_i915_gem_object *obj)
 {
-	if (!READ_ONCE(obj->pin_global))
+	if (!i915_gem_object_is_framebuffer(obj))
 		return;
 
 	i915_gem_object_lock(obj);
@@ -422,12 +422,8 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
 
 	assert_object_held(obj);
 
-	/* Mark the global pin early so that we account for the
-	 * display coherency whilst setting up the cache domains.
-	 */
-	obj->pin_global++;
-
-	/* The display engine is not coherent with the LLC cache on gen6.  As
+	/*
+	 * The display engine is not coherent with the LLC cache on gen6.  As
 	 * a result, we make sure that the pinning that is about to occur is
 	 * done with uncached PTEs. This is lowest common denominator for all
 	 * chipsets.
@@ -439,12 +435,11 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
 	ret = i915_gem_object_set_cache_level(obj,
 					      HAS_WT(to_i915(obj->base.dev)) ?
 					      I915_CACHE_WT : I915_CACHE_NONE);
-	if (ret) {
-		vma = ERR_PTR(ret);
-		goto err_unpin_global;
-	}
+	if (ret)
+		return ERR_PTR(ret);
 
-	/* As the user may map the buffer once pinned in the display plane
+	/*
+	 * As the user may map the buffer once pinned in the display plane
 	 * (e.g. libkms for the bootup splash), we have to ensure that we
 	 * always use map_and_fenceable for all scanout buffers. However,
 	 * it may simply be too big to fit into mappable, in which case
@@ -461,22 +456,19 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
 	if (IS_ERR(vma))
 		vma = i915_gem_object_ggtt_pin(obj, view, 0, alignment, flags);
 	if (IS_ERR(vma))
-		goto err_unpin_global;
+		return vma;
 
 	vma->display_alignment = max_t(u64, vma->display_alignment, alignment);
 
 	__i915_gem_object_flush_for_display(obj);
 
-	/* It should now be out of any other write domains, and we can update
+	/*
+	 * It should now be out of any other write domains, and we can update
 	 * the domain values for our changes.
 	 */
 	obj->read_domains |= I915_GEM_DOMAIN_GTT;
 
 	return vma;
-
-err_unpin_global:
-	obj->pin_global--;
-	return vma;
 }
 
 static void i915_gem_object_bump_inactive_ggtt(struct drm_i915_gem_object *obj)
@@ -514,12 +506,6 @@ i915_gem_object_unpin_from_display_plane(struct i915_vma *vma)
 
 	assert_object_held(obj);
 
-	if (WARN_ON(obj->pin_global == 0))
-		return;
-
-	if (--obj->pin_global == 0)
-		vma->display_alignment = I915_GTT_MIN_ALIGNMENT;
-
 	/* Bump the LRU to try and avoid premature eviction whilst flipping  */
 	i915_gem_object_bump_inactive_ggtt(obj);