st/dri: Implement the new dri2 throttling extension

But don't hook it up just yet until we figure out a good way to do that.
Also, we should, in the future, add driconf options to control what
throttling reasons should be honored, and the number of outstanding
swaps allowed.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>

src/gallium/state_trackers/dri/common/dri_drawable.c

@@ -37,7 +37,9 @@
 #include "util/u_format.h"
 #include "util/u_memory.h"
 #include "util/u_inlines.h"
- 
+
+static void
+swap_fences_unref(struct dri_drawable *draw);
 
 static boolean
 dri_st_framebuffer_validate(struct st_framebuffer_iface *stfbi,
@@ -135,6 +137,8 @@ dri_create_buffer(__DRIscreen * sPriv,
    drawable->screen = screen;
    drawable->sPriv = sPriv;
    drawable->dPriv = dPriv;
+   drawable->desired_fences = 2;
+
    dPriv->driverPrivate = (void *)drawable;
    p_atomic_set(&drawable->base.stamp, 1);
 
@@ -155,6 +159,8 @@ dri_destroy_buffer(__DRIdrawable * dPriv)
    for (i = 0; i < ST_ATTACHMENT_COUNT; i++)
       pipe_resource_reference(&drawable->textures[i], NULL);
 
+   swap_fences_unref(drawable);
+
    FREE(drawable);
 }
 
@@ -266,4 +272,122 @@ dri_drawable_get_format(struct dri_drawable *drawable,
    }
 }
 
+
+/**
+ * swap_fences_pop_front - pull a fence from the throttle queue
+ *
+ * If the throttle queue is filled to the desired number of fences,
+ * pull fences off the queue until the number is less than the desired
+ * number of fences, and return the last fence pulled.
+ */
+static struct pipe_fence_handle *
+swap_fences_pop_front(struct dri_drawable *draw)
+{
+   struct pipe_screen *screen = draw->screen->base.screen;
+   struct pipe_fence_handle *fence = NULL;
+
+   if (draw->desired_fences == 0)
+      return NULL;
+
+   if (draw->cur_fences >= draw->desired_fences) {
+      screen->fence_reference(screen, &fence, draw->swap_fences[draw->tail]);
+      screen->fence_reference(screen, &draw->swap_fences[draw->tail++], NULL);
+      draw->tail &= DRI_SWAP_FENCES_MASK;
+      --draw->cur_fences;
+   }
+   return fence;
+}
+
+
+/**
+ * swap_fences_push_back - push a fence onto the throttle queue
+ *
+ * push a fence onto the throttle queue and pull fences of the queue
+ * so that the desired number of fences are on the queue.
+ */
+static void
+swap_fences_push_back(struct dri_drawable *draw,
+		      struct pipe_fence_handle *fence)
+{
+   struct pipe_screen *screen = draw->screen->base.screen;
+
+   if (!fence || draw->desired_fences == 0)
+      return;
+
+   while(draw->cur_fences == draw->desired_fences)
+      swap_fences_pop_front(draw);
+
+   draw->cur_fences++;
+   screen->fence_reference(screen, &draw->swap_fences[draw->head++],
+			   fence);
+   draw->head &= DRI_SWAP_FENCES_MASK;
+}
+
+
+/**
+ * swap_fences_unref - empty the throttle queue
+ *
+ * pulls fences of the throttle queue until it is empty.
+ */
+static void
+swap_fences_unref(struct dri_drawable *draw)
+{
+   struct pipe_screen *screen = draw->screen->base.screen;
+
+   while(draw->cur_fences) {
+      screen->fence_reference(screen, &draw->swap_fences[draw->tail++], NULL);
+      draw->tail &= DRI_SWAP_FENCES_MASK;
+      --draw->cur_fences;
+   }
+}
+
+
+/**
+ * dri_throttle - A DRI2ThrottleExtension throttling function.
+ *
+ * pulls a fence off the throttling queue and waits for it if the
+ * number of fences on the throttling queue has reached the desired
+ * number.
+ *
+ * Then flushes to insert a fence at the current rendering position, and
+ * pushes that fence on the queue. This requires that the st_context_iface
+ * flush method returns a fence even if there are no commands to flush.
+ */
+static void
+dri_throttle(__DRIcontext *driCtx, __DRIdrawable *dPriv,
+	     enum __DRI2throttleReason reason)
+{
+    struct dri_drawable *draw = dri_drawable(dPriv);
+    struct st_context_iface *ctxi;
+    struct pipe_screen *screen = draw->screen->base.screen;
+    struct pipe_fence_handle *fence;
+
+    if (reason != __DRI2_THROTTLE_SWAPBUFFER &&
+	reason != __DRI2_THROTTLE_FLUSHFRONT)
+	return;
+
+    fence = swap_fences_pop_front(draw);
+    if (fence) {
+	(void) screen->fence_finish(screen, fence, PIPE_TIMEOUT_INFINITE);
+	screen->fence_reference(screen, &fence, NULL);
+    }
+
+    if (driCtx == NULL)
+	return;
+
+    ctxi = dri_context(driCtx)->st;
+    ctxi->flush(ctxi, 0, &fence);
+    if (fence) {
+	swap_fences_push_back(draw, fence);
+	screen->fence_reference(screen, &fence, NULL);
+    }
+}
+
+
+const __DRI2throttleExtension dri2ThrottleExtension = {
+    .base = { __DRI2_THROTTLE, __DRI2_THROTTLE_VERSION },
+    .throttle = dri_throttle,
+};
+
+
 /* vim: set sw=3 ts=8 sts=3 expandtab: */

src/gallium/state_trackers/dri/common/dri_drawable.h

@@ -36,6 +36,10 @@ struct pipe_surface;
 struct st_framebuffer;
 struct dri_context;
 
+#define DRI_SWAP_FENCES_MAX 4
+#define DRI_SWAP_FENCES_MASK 3
+#define DRI_SWAP_FENCES_DEFAULT 1
+
 struct dri_drawable
 {
    struct st_framebuffer_iface base;
@@ -55,6 +59,12 @@ struct dri_drawable
    struct pipe_resource *textures[ST_ATTACHMENT_COUNT];
    unsigned int texture_mask, texture_stamp;
 
+   struct pipe_fence_handle *swap_fences[DRI_SWAP_FENCES_MAX];
+   unsigned int cur_fences;
+   unsigned int head;
+   unsigned int tail;
+   unsigned int desired_fences;
+
    /* used only by DRISW */
    struct pipe_surface *drisw_surface;
 
@@ -93,7 +103,7 @@ dri_drawable_get_format(struct dri_drawable *drawable,
                         unsigned *bind);
 
 extern const __DRItexBufferExtension driTexBufferExtension;
-
+extern const __DRI2throttleExtension dri2ThrottleExtension;
 #endif
 
 /* vim: set sw=3 ts=8 sts=3 expandtab: */