drm/nv50: fix iommu errors caused by device reading from address 0

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/gpu/drm/nouveau/nv50_fb.c b/drivers/gpu/drm/nouveau/nv50_fb.c
index a95e6941ba88..32611bd30e6d 100644
--- a/drivers/gpu/drm/nouveau/nv50_fb.c
+++ b/drivers/gpu/drm/nouveau/nv50_fb.c
@@ -6,10 +6,16 @@
 int
 nv50_fb_init(struct drm_device *dev)
 {
-        /* This is needed to get meaningful information from 100c90
-         * on traps. No idea what these values mean exactly. */
         struct drm_nouveau_private *dev_priv = dev->dev_private;
 
+        /* Not a clue what this is exactly.  Without pointing it at a
+         * scratch page, VRAM->GART blits with M2MF (as in DDX DFS)
+         * cause IOMMU "read from address 0" errors (rh#561267)
+         */
+        nv_wr32(dev, 0x100c08, dev_priv->gart_info.sg_dummy_bus >> 8);
+
+        /* This is needed to get meaningful information from 100c90
+         * on traps. No idea what these values mean exactly. */
         switch (dev_priv->chipset) {
         case 0x50:
                 nv_wr32(dev, 0x100c90, 0x0707ff);