intel-gem: Disable tiling if we get junk from the MCHBAR read.

One of our systems has been returning 0xffffffff from all MCHBAR reads, which
means we'll need to figure out why, or add an alternate detection method.

diff --git a/linux-core/i915_gem_tiling.c b/linux-core/i915_gem_tiling.c
index d66276d61618076b4b79c48b0c4189bcac770626..ddf83ce4f6b5ade955c482e7cb9a36a0524b5579 100644 (file)
--- a/linux-core/i915_gem_tiling.c
+++ b/linux-core/i915_gem_tiling.c
@@ -155,7 +155,10 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
                 */
                chdecmisc = readb(mchbar + CHDECMISC);
 
-               if (chdecmisc & CHDECMISC_FLEXMEMORY) {
+               if (chdecmisc == 0xff) {
+                       DRM_ERROR("Couldn't read from MCHBAR.  "
+                                 "Disabling tiling.\n");
+               } else if (chdecmisc & CHDECMISC_FLEXMEMORY) {
                        swizzle_x = I915_BIT_6_SWIZZLE_NONE;
                        swizzle_y = I915_BIT_6_SWIZZLE_NONE;
                } else {
@@ -197,6 +200,12 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
                        }
                        break;
                }
+               if (dcc == 0xffffffff) {
+                       DRM_ERROR("Couldn't read from MCHBAR.  "
+                                 "Disabling tiling.\n");
+                       swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
+                       swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
+               }
        }
 
        iounmap(mchbar);