intel: Do temporary CPU maps of textures that are too big to GTT map.

This still fails, since 8192*4bpp == 32768, which is too big to use the
blitter on.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

src/mesa/drivers/dri/intel/intel_mipmap_tree.c

@@ -1703,6 +1703,23 @@ intel_miptree_map_singlesample(struct intel_context *intel,
 {
    struct intel_miptree_map *map;
 
+   /* Estimate the size of the mappable aperture into the GTT.  There's an
+    * ioctl to get the whole GTT size, but not one to get the mappable subset.
+    * It turns out it's basically always 256MB, though some ancient hardware
+    * was smaller.
+    */
+   uint32_t gtt_size = 256 * 1024 * 1024;
+   if (intel->gen == 2)
+      gtt_size = 128 * 1024 * 1024;
+
+   /* We don't want to map two objects such that a memcpy between them would
+    * just fault one mapping in and then the other over and over forever.  So
+    * we would need to divide the GTT size by 2.  Additionally, some GTT is
+    * taken up by things like the framebuffer and the ringbuffer and such, so
+    * be more conservative.
+    */
+   uint32_t max_gtt_map_object_size = gtt_size / 4;
+
    assert(mt->num_samples <= 1);
 
    map = intel_miptree_attach_map(mt, level, slice, x, y, w, h, mode);
@@ -1749,6 +1766,10 @@ intel_miptree_map_singlesample(struct intel_context *intel,
             mt->region->tiling == I915_TILING_X &&
             mt->region->pitch < 32768) {
       intel_miptree_map_blit(intel, mt, map, level, slice);
+   } else if (mt->region->tiling != I915_TILING_NONE &&
+              mt->region->bo->size >= max_gtt_map_object_size) {
+      assert(mt->region->pitch < 32768);
+      intel_miptree_map_blit(intel, mt, map, level, slice);
    } else {
       intel_miptree_map_gtt(intel, mt, map, level, slice);
    }