sna: Reset the source counter if we completely dirty the CPU pixmap

For a long lived pixmap which we are repeatedly using for upload and
copying to other pixmaps, we don't want to keep to maintain a GPU
buffer. So instead, reset the source counter if we discard the GPU bo
and treat the pixmap as purely CPU.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/sna/sna_accel.c

@@ -166,6 +166,9 @@ static void sna_pixmap_destroy_gpu_bo(struct sna *sna, struct sna_pixmap *priv)
 {
 	kgem_bo_destroy(&sna->kgem, priv->gpu_bo);
 	priv->gpu_bo = NULL;
+
+	/* and reset the upload counter */
+	priv->source_count = SOURCE_BIAS;
 }
 
 static Bool sna_destroy_private(PixmapPtr pixmap, struct sna_pixmap *priv)