drm/nv50: implement possible workaround for NV86 PGRAPH TLB flush hang

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nouveau_state.c b/drivers/gpu/drm/nouveau/nouveau_state.c
index ea34521..049f755 100644
--- a/drivers/gpu/drm/nouveau/nouveau_state.c
+++ b/drivers/gpu/drm/nouveau/nouveau_state.c
@@ -354,6 +354,15 @@
 		engine->graph.destroy_context	= nv50_graph_destroy_context;
 		engine->graph.load_context	= nv50_graph_load_context;
 		engine->graph.unload_context	= nv50_graph_unload_context;
+		if (dev_priv->chipset != 0x86)
+			engine->graph.tlb_flush	= nv50_graph_tlb_flush;
+		else {
+			/* from what i can see nvidia do this on every
+			 * pre-NVA3 board except NVAC, but, we've only
+			 * ever seen problems on NV86
+			 */
+			engine->graph.tlb_flush	= nv86_graph_tlb_flush;
+		}
 		engine->fifo.channels		= 128;
 		engine->fifo.init		= nv50_fifo_init;
 		engine->fifo.takedown		= nv50_fifo_takedown;
@@ -365,6 +374,7 @@
 		engine->fifo.destroy_context	= nv50_fifo_destroy_context;
 		engine->fifo.load_context	= nv50_fifo_load_context;
 		engine->fifo.unload_context	= nv50_fifo_unload_context;
+		engine->fifo.tlb_flush		= nv50_fifo_tlb_flush;
 		engine->display.early_init	= nv50_display_early_init;
 		engine->display.late_takedown	= nv50_display_late_takedown;
 		engine->display.create		= nv50_display_create;