nvc0: enable shader watchdog timer

Prevent infinite loops in shaders from locking up the GPU.

src/gallium/drivers/nvc0/nvc0_3d.xml.h

@@ -315,6 +315,8 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #define NVC0_3D_PATCH_VERTICES					0x00000dcc
 
+#define NVC0_3D_WATCHDOG_TIMER					0x00000de4
+
 #define NVC0_3D_WINDOW_OFFSET_X					0x00000df8
 
 #define NVC0_3D_WINDOW_OFFSET_Y					0x00000dfc

src/gallium/drivers/nvc0/nvc0_screen.c

@@ -466,6 +466,12 @@ nvc0_screen_create(struct nouveau_device *dev)
    BEGIN_RING(chan, RING_3D(COND_MODE), 1);
    OUT_RING  (chan, NVC0_3D_COND_MODE_ALWAYS);
 
+   if (debug_get_bool_option("NOUVEAU_SHADER_WATCHDOG", TRUE)) {
+      /* kill shaders after about 1 second (at 100 MHz) */
+      BEGIN_RING(chan, RING_3D(WATCHDOG_TIMER), 1);
+      OUT_RING  (chan, 0x17);
+   }
+
    BEGIN_RING(chan, RING_3D(RT_CONTROL), 1);
    OUT_RING  (chan, 1);