drm: add option to force writeback off.

In order to get some better debugging from people about certain hangs/crashes
we need to be able to turn AGP writeback off permanently...

Signed-off-by: Dave Airlie <airlied@linux.ie>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/char/drm/radeon_cp.c b/drivers/char/drm/radeon_cp.c
index 447bfbe0da8a..e64d680899f5 100644
--- a/drivers/char/drm/radeon_cp.c
+++ b/drivers/char/drm/radeon_cp.c
@@ -1205,6 +1205,10 @@ static void radeon_cp_init_ring_buffer(drm_device_t * dev,
                 dev_priv->writeback_works = 0;
                 DRM_DEBUG("writeback test failed\n");
         }
+        if (radeon_no_wb == 1) {
+                dev_priv->writeback_works = 0;
+                DRM_DEBUG("writeback forced off\n");
+        }
 
         dev_priv->sarea_priv->last_frame = dev_priv->scratch[0] = 0;
         RADEON_WRITE(RADEON_LAST_FRAME_REG, dev_priv->sarea_priv->last_frame);