drm/i915: Introduce accurate frontbuffer tracking

So from just a quick look we seem to have enough information to
accurately figure out whether a given gem bo is used as a frontbuffer
and where exactly: We have obj->pin_count as a first check with no
false negatives and only negligible false positives. And then we can
just walk the modeset objects and figure out where exactly a buffer is
used as scanout.

Except that we can't due to locking order: If we already hold
dev->struct_mutex we can't acquire any modeset locks, so could
potential chase freed pointers and other evil stuff.

So we need something else. For that introduce a new set of bits
obj->frontbuffer_bits to track where a buffer object is used. That we
can then chase without grabbing any modeset locks.

Of course the consumers of this (DRRS, PSR, FBC, ...) still need to be
able to do their magic both when called from modeset and from gem
code. But that can be easily achieved by adding locks for these
specific subsystems which always nest within either kms or gem
locking.

This patch just adds the relevant update code to all places.

Note that if we ever support multi-planar scanout targets then we need
one frontbuffer tracking bit per attachment point that we expose to
userspace.

v2:
- Fix more oopsen. Oops.
- WARN if we leak obj->frontbuffer_bits when freeing a gem buffer. Fix
  the bugs this brought to light.
- s/update_frontbuffer_bits/update_fb_bits/. More consistent with the
  fb tracking functions (fb for gem object, frontbuffer for raw bits).
  And the function name was way too long.

v3: Size obj->frontbuffer_bits correctly so that all pipes fit in.

v4: Don't update fb bits in set_base on failure. Noticed by Chris.

v5: s/i915_gem_update_fb_bits/i915_gem_track_fb/ Also remove a few
local enum pipe variables which are now no longer needed to make the
function arguments no drop over the 80 char limit.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1593,6 +1593,26 @@ struct drm_i915_gem_object_ops {
 	void (*release)(struct drm_i915_gem_object *);
 };
 
+/*
+ * Frontbuffer tracking bits. Set in obj->frontbuffer_bits while a gem bo is
+ * considered to be the frontbuffer for the given plane interface-vise. This
+ * doesn't mean that the hw necessarily already scans it out, but that any
+ * rendering (by the cpu or gpu) will land in the frontbuffer eventually.
+ *
+ * We have one bit per pipe and per scanout plane type.
+ */
+#define INTEL_FRONTBUFFER_BITS_PER_PIPE 4
+#define INTEL_FRONTBUFFER_BITS \
+	(INTEL_FRONTBUFFER_BITS_PER_PIPE * I915_MAX_PIPES)
+#define INTEL_FRONTBUFFER_PRIMARY(pipe) \
+	(1 << (INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe)))
+#define INTEL_FRONTBUFFER_CURSOR(pipe) \
+	(1 << (1 +(INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe))))
+#define INTEL_FRONTBUFFER_SPRITE(pipe) \
+	(1 << (2 +(INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe))))
+#define INTEL_FRONTBUFFER_OVERLAY(pipe) \
+	(1 << (3 +(INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe))))
+
 struct drm_i915_gem_object {
 	struct drm_gem_object base;
 
@@ -1680,6 +1700,8 @@ struct drm_i915_gem_object {
 	unsigned int has_global_gtt_mapping:1;
 	unsigned int has_dma_mapping:1;
 
+	unsigned int frontbuffer_bits:INTEL_FRONTBUFFER_BITS;
+
 	struct sg_table *pages;
 	int pages_pin_count;
 
@@ -1726,6 +1748,10 @@ struct drm_i915_gem_object {
 };
 #define to_intel_bo(x) container_of(x, struct drm_i915_gem_object, base)
 
+void i915_gem_track_fb(struct drm_i915_gem_object *old,
+		       struct drm_i915_gem_object *new,
+		       unsigned frontbuffer_bits);
+
 /**
  * Request queue structure.
  *

drivers/gpu/drm/i915/i915_gem.c

@@ -4452,6 +4452,8 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	if (obj->stolen)
 		i915_gem_object_unpin_pages(obj);
 
+	WARN_ON(obj->frontbuffer_bits);
+
 	if (WARN_ON(obj->pages_pin_count))
 		obj->pages_pin_count = 0;
 	if (discard_backing_storage(obj))
@@ -4996,6 +4998,23 @@ int i915_gem_open(struct drm_device *dev, struct drm_file *file)
 	return ret;
 }
 
+void i915_gem_track_fb(struct drm_i915_gem_object *old,
+		       struct drm_i915_gem_object *new,
+		       unsigned frontbuffer_bits)
+{
+	if (old) {
+		WARN_ON(!mutex_is_locked(&old->base.dev->struct_mutex));
+		WARN_ON(!(old->frontbuffer_bits & frontbuffer_bits));
+		old->frontbuffer_bits &= ~frontbuffer_bits;
+	}
+
+	if (new) {
+		WARN_ON(!mutex_is_locked(&new->base.dev->struct_mutex));
+		WARN_ON(new->frontbuffer_bits & frontbuffer_bits);
+		new->frontbuffer_bits |= frontbuffer_bits;
+	}
+}
+
 static bool mutex_is_locked_by(struct mutex *mutex, struct task_struct *task)
 {
 	if (!mutex_is_locked(mutex))

drivers/gpu/drm/i915/intel_display.c

@@ -2351,6 +2351,7 @@ static bool intel_alloc_plane_obj(struct intel_crtc *crtc,
 		goto out_unref_obj;
 	}
 
+	obj->frontbuffer_bits = INTEL_FRONTBUFFER_PRIMARY(crtc->pipe);
 	mutex_unlock(&dev->struct_mutex);
 
 	DRM_DEBUG_KMS("plane fb obj %p\n", obj);
@@ -2396,6 +2397,7 @@ static void intel_find_plane_obj(struct intel_crtc *intel_crtc,
 		if (i915_gem_obj_ggtt_offset(fb->obj) == plane_config->base) {
 			drm_framebuffer_reference(c->primary->fb);
 			intel_crtc->base.primary->fb = c->primary->fb;
+			fb->obj->frontbuffer_bits |= INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe);
 			break;
 		}
 	}
@@ -2684,7 +2686,9 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 	struct drm_device *dev = crtc->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	enum pipe pipe = intel_crtc->pipe;
 	struct drm_framebuffer *old_fb;
+	struct drm_i915_gem_object *obj = to_intel_framebuffer(fb)->obj;
 	int ret;
 
 	if (intel_crtc_has_pending_flip(crtc)) {
@@ -2705,10 +2709,13 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 		return -EINVAL;
 	}
 
+	old_fb = crtc->primary->fb;
+
 	mutex_lock(&dev->struct_mutex);
-	ret = intel_pin_and_fence_fb_obj(dev,
-					 to_intel_framebuffer(fb)->obj,
-					 NULL);
+	ret = intel_pin_and_fence_fb_obj(dev, obj, NULL);
+	if (ret == 0)
+		i915_gem_track_fb(to_intel_framebuffer(old_fb)->obj, obj,
+				  INTEL_FRONTBUFFER_PRIMARY(pipe));
 	mutex_unlock(&dev->struct_mutex);
 	if (ret != 0) {
 		DRM_ERROR("pin & fence failed\n");
@@ -2748,7 +2755,6 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 
 	dev_priv->display.update_primary_plane(crtc, fb, x, y);
 
-	old_fb = crtc->primary->fb;
 	crtc->primary->fb = fb;
 	crtc->x = x;
 	crtc->y = y;
@@ -4922,6 +4928,8 @@ static void intel_crtc_disable(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct drm_connector *connector;
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_i915_gem_object *old_obj;
+	enum pipe pipe = to_intel_crtc(crtc)->pipe;
 
 	/* crtc should still be enabled when we disable it. */
 	WARN_ON(!crtc->enabled);
@@ -4931,12 +4939,15 @@ static void intel_crtc_disable(struct drm_crtc *crtc)
 	dev_priv->display.off(crtc);
 
 	assert_plane_disabled(dev->dev_private, to_intel_crtc(crtc)->plane);
-	assert_cursor_disabled(dev_priv, to_intel_crtc(crtc)->pipe);
-	assert_pipe_disabled(dev->dev_private, to_intel_crtc(crtc)->pipe);
+	assert_cursor_disabled(dev_priv, pipe);
+	assert_pipe_disabled(dev->dev_private, pipe);
 
 	if (crtc->primary->fb) {
+		old_obj = to_intel_framebuffer(crtc->primary->fb)->obj;
 		mutex_lock(&dev->struct_mutex);
-		intel_unpin_fb_obj(to_intel_framebuffer(crtc->primary->fb)->obj);
+		intel_unpin_fb_obj(old_obj);
+		i915_gem_track_fb(old_obj, NULL,
+				  INTEL_FRONTBUFFER_PRIMARY(pipe));
 		mutex_unlock(&dev->struct_mutex);
 		crtc->primary->fb = NULL;
 	}
@@ -8103,6 +8114,7 @@ static int intel_crtc_cursor_set_obj(struct drm_crtc *crtc,
 	struct drm_device *dev = crtc->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	enum pipe pipe = intel_crtc->pipe;
 	unsigned old_width;
 	uint32_t addr;
 	int ret;
@@ -8182,6 +8194,8 @@ static int intel_crtc_cursor_set_obj(struct drm_crtc *crtc,
 			i915_gem_object_unpin_from_display_plane(intel_crtc->cursor_bo);
 	}
 
+	i915_gem_track_fb(intel_crtc->cursor_bo, obj,
+			  INTEL_FRONTBUFFER_CURSOR(pipe));
 	mutex_unlock(&dev->struct_mutex);
 
 	old_width = intel_crtc->cursor_width;
@@ -9404,6 +9418,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 	struct drm_framebuffer *old_fb = crtc->primary->fb;
 	struct drm_i915_gem_object *obj = to_intel_framebuffer(fb)->obj;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	enum pipe pipe = intel_crtc->pipe;
 	struct intel_unpin_work *work;
 	struct intel_engine_cs *ring;
 	unsigned long flags;
@@ -9475,7 +9490,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
 
 	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
-		work->flip_count = I915_READ(PIPE_FLIPCOUNT_GM45(intel_crtc->pipe)) + 1;
+		work->flip_count = I915_READ(PIPE_FLIPCOUNT_GM45(pipe)) + 1;
 
 	if (IS_VALLEYVIEW(dev)) {
 		ring = &dev_priv->ring[BCS];
@@ -9503,6 +9518,9 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 	if (ret)
 		goto cleanup_unpin;
 
+	i915_gem_track_fb(work->old_fb_obj, obj,
+			  INTEL_FRONTBUFFER_PRIMARY(pipe));
+
 	intel_disable_fbc(dev);
 	intel_mark_fb_busy(obj, NULL);
 	mutex_unlock(&dev->struct_mutex);
@@ -9534,7 +9552,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 		intel_crtc_wait_for_pending_flips(crtc);
 		ret = intel_pipe_set_base(crtc, crtc->x, crtc->y, fb);
 		if (ret == 0 && event)
-			drm_send_vblank_event(dev, intel_crtc->pipe, event);
+			drm_send_vblank_event(dev, pipe, event);
 	}
 	return ret;
 }
@@ -10569,10 +10587,13 @@ static int __intel_set_mode(struct drm_crtc *crtc,
 	 */
 	for_each_intel_crtc_masked(dev, modeset_pipes, intel_crtc) {
 		struct drm_framebuffer *old_fb;
+		struct drm_i915_gem_object *old_obj = NULL;
+		struct drm_i915_gem_object *obj =
+			to_intel_framebuffer(fb)->obj;
 
 		mutex_lock(&dev->struct_mutex);
 		ret = intel_pin_and_fence_fb_obj(dev,
-						 to_intel_framebuffer(fb)->obj,
+						 obj,
 						 NULL);
 		if (ret != 0) {
 			DRM_ERROR("pin & fence failed\n");
@@ -10580,8 +10601,12 @@ static int __intel_set_mode(struct drm_crtc *crtc,
 			goto done;
 		}
 		old_fb = crtc->primary->fb;
-		if (old_fb)
-			intel_unpin_fb_obj(to_intel_framebuffer(old_fb)->obj);
+		if (old_fb) {
+			old_obj = to_intel_framebuffer(old_fb)->obj;
+			intel_unpin_fb_obj(old_obj);
+		}
+		i915_gem_track_fb(old_obj, obj,
+				  INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe));
 		mutex_unlock(&dev->struct_mutex);
 
 		crtc->primary->fb = fb;
@@ -11196,8 +11221,9 @@ intel_primary_plane_disable(struct drm_plane *plane)
 	intel_crtc_wait_for_pending_flips(plane->crtc);
 	intel_disable_primary_hw_plane(dev_priv, intel_plane->plane,
 				       intel_plane->pipe);
-
 disable_unpin:
+	i915_gem_track_fb(to_intel_framebuffer(plane->fb)->obj, NULL,
+			  INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe));
 	intel_unpin_fb_obj(to_intel_framebuffer(plane->fb)->obj);
 	plane->fb = NULL;
 
@@ -11215,6 +11241,7 @@ intel_primary_plane_setplane(struct drm_plane *plane, struct drm_crtc *crtc,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
 	struct intel_plane *intel_plane = to_intel_plane(plane);
+	struct drm_i915_gem_object *obj, *old_obj = NULL;
 	struct drm_rect dest = {
 		/* integer pixels */
 		.x1 = crtc_x,
@@ -11246,6 +11273,10 @@ intel_primary_plane_setplane(struct drm_plane *plane, struct drm_crtc *crtc,
 	if (ret)
 		return ret;
 
+	if (plane->fb)
+		old_obj = to_intel_framebuffer(plane->fb)->obj;
+	obj = to_intel_framebuffer(fb)->obj;
+
 	/*
 	 * If the CRTC isn't enabled, we're just pinning the framebuffer,
 	 * updating the fb pointer, and returning without touching the
@@ -11258,12 +11289,13 @@ intel_primary_plane_setplane(struct drm_plane *plane, struct drm_crtc *crtc,
 		 * we may have an fb pinned; unpin it.
 		 */
 		if (plane->fb)
-			intel_unpin_fb_obj(to_intel_framebuffer(plane->fb)->obj);
+			intel_unpin_fb_obj(old_obj);
+
+		i915_gem_track_fb(old_obj, obj,
+				  INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe));
 
 		/* Pin and return without programming hardware */
-		return intel_pin_and_fence_fb_obj(dev,
-						  to_intel_framebuffer(fb)->obj,
-						  NULL);
+		return intel_pin_and_fence_fb_obj(dev, obj, NULL);
 	}
 
 	intel_crtc_wait_for_pending_flips(crtc);
@@ -11280,13 +11312,14 @@ intel_primary_plane_setplane(struct drm_plane *plane, struct drm_crtc *crtc,
 		 * fail.
 		 */
 		if (plane->fb != fb) {
-			ret = intel_pin_and_fence_fb_obj(dev,
-							 to_intel_framebuffer(fb)->obj,
-							 NULL);
+			ret = intel_pin_and_fence_fb_obj(dev, obj, NULL);
 			if (ret)
 				return ret;
 		}
 
+		i915_gem_track_fb(old_obj, obj,
+				  INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe));
+
 		if (intel_crtc->primary_enabled)
 			intel_disable_primary_hw_plane(dev_priv,
 						       intel_plane->plane,
@@ -11295,7 +11328,7 @@ intel_primary_plane_setplane(struct drm_plane *plane, struct drm_crtc *crtc,
 
 		if (plane->fb != fb)
 			if (plane->fb)
-				intel_unpin_fb_obj(to_intel_framebuffer(plane->fb)->obj);
+				intel_unpin_fb_obj(old_obj);
 
 		return 0;
 	}

drivers/gpu/drm/i915/intel_overlay.c

@@ -415,6 +415,10 @@ static int intel_overlay_release_old_vid(struct intel_overlay *overlay)
 	}
 
 	intel_overlay_release_old_vid_tail(overlay);
+
+
+	i915_gem_track_fb(overlay->old_vid_bo, NULL,
+			  INTEL_FRONTBUFFER_OVERLAY(overlay->crtc->pipe));
 	return 0;
 }
 
@@ -686,6 +690,7 @@ static int intel_overlay_do_put_image(struct intel_overlay *overlay,
 	bool scale_changed = false;
 	struct drm_device *dev = overlay->dev;
 	u32 swidth, swidthsw, sheight, ostride;
+	enum pipe pipe = overlay->crtc->pipe;
 
 	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
 	BUG_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
@@ -713,7 +718,7 @@ static int intel_overlay_do_put_image(struct intel_overlay *overlay,
 		oconfig = OCONF_CC_OUT_8BIT;
 		if (IS_GEN4(overlay->dev))
 			oconfig |= OCONF_CSC_MODE_BT709;
-		oconfig |= overlay->crtc->pipe == 0 ?
+		oconfig |= pipe == 0 ?
 			OCONF_PIPE_A : OCONF_PIPE_B;
 		iowrite32(oconfig, &regs->OCONFIG);
 		intel_overlay_unmap_regs(overlay, regs);
@@ -776,6 +781,9 @@ static int intel_overlay_do_put_image(struct intel_overlay *overlay,
 	if (ret)
 		goto out_unpin;
 
+	i915_gem_track_fb(overlay->vid_bo, new_bo,
+			  INTEL_FRONTBUFFER_OVERLAY(pipe));
+
 	overlay->old_vid_bo = overlay->vid_bo;
 	overlay->vid_bo = new_bo;
 

drivers/gpu/drm/i915/intel_sprite.c

@@ -811,6 +811,7 @@ intel_update_plane(struct drm_plane *plane, struct drm_crtc *crtc,
 	struct drm_device *dev = plane->dev;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
 	struct intel_plane *intel_plane = to_intel_plane(plane);
+	enum pipe pipe = intel_crtc->pipe;
 	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
 	struct drm_i915_gem_object *obj = intel_fb->obj;
 	struct drm_i915_gem_object *old_obj = intel_plane->obj;
@@ -998,6 +999,8 @@ intel_update_plane(struct drm_plane *plane, struct drm_crtc *crtc,
 	 */
 	ret = intel_pin_and_fence_fb_obj(dev, obj, NULL);
 
+	i915_gem_track_fb(old_obj, obj,
+			  INTEL_FRONTBUFFER_SPRITE(pipe));
 	mutex_unlock(&dev->struct_mutex);
 
 	if (ret)
@@ -1062,6 +1065,7 @@ intel_disable_plane(struct drm_plane *plane)
 	struct drm_device *dev = plane->dev;
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 	struct intel_crtc *intel_crtc;
+	enum pipe pipe;
 
 	if (!plane->fb)
 		return 0;
@@ -1070,6 +1074,7 @@ intel_disable_plane(struct drm_plane *plane)
 		return -EINVAL;
 
 	intel_crtc = to_intel_crtc(plane->crtc);
+	pipe = intel_crtc->pipe;
 
 	if (intel_crtc->active) {
 		bool primary_was_enabled = intel_crtc->primary_enabled;
@@ -1088,6 +1093,8 @@ intel_disable_plane(struct drm_plane *plane)
 
 		mutex_lock(&dev->struct_mutex);
 		intel_unpin_fb_obj(intel_plane->obj);
+		i915_gem_track_fb(intel_plane->obj, NULL,
+				  INTEL_FRONTBUFFER_SPRITE(pipe));
 		mutex_unlock(&dev->struct_mutex);
 
 		intel_plane->obj = NULL;