drm/i915: fix the CFB size check

In function find_compression_threshold() we try to over-allocate CFB
space in order to reduce reallocations and fragmentation, and we're
not considering that at the CFB size check. Consider it.

There is also a longer-term plan to kill
dev_priv->fbc.uncompressed_size, but this will come later.

v2: Use drm_mm_node_allocated() (Chris).
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/

drivers/gpu/drm/i915/intel_fbc.c

@@ -720,7 +720,8 @@ static int intel_fbc_setup_cfb(struct intel_crtc *crtc)
 	size = intel_fbc_calculate_cfb_size(crtc);
 	cpp = drm_format_plane_cpp(fb->pixel_format, 0);
 
-	if (size <= dev_priv->fbc.uncompressed_size)
+	if (drm_mm_node_allocated(&dev_priv->fbc.compressed_fb) &&
+	    size <= dev_priv->fbc.compressed_fb.size * dev_priv->fbc.threshold)
 		return 0;
 
 	/* Release any current block */