drm/i915: fix up tiling/fence reg setup on i8xx class hw

This fixes all the tiling problems with the 2d ddx. glxgears still doesn't work.
Changes:

- fix a copy&paste error in i8xx fence reg setup. It resulted in an at most a
  512KB offset of the fence reg window, so was only visible sometimes.
- add tests for stride and object size constrains (also for i915 and 1965 class
  hw). Userspace seems to have an of-by-one bug there, which changes the fence
  size by at most 512KB due to an overflow.
- because i8xx hw is quite old (and therefore not as well-tested) I left 2 debug
  WARN_ONs in the i8xx fence reg setup code to hopefully catch any further
  overflows in the bit-fields. Lastly there's one small change to make the
  alignment checks more consistent.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=20289
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_gem_tiling.c

@@ -216,6 +216,22 @@ i915_tiling_ok(struct drm_device *dev, int stride, int size, int tiling_mode)
 	else
 		tile_width = 512;
 
+	/* check maximum stride & object size */
+	if (IS_I965G(dev)) {
+		/* i965 stores the end address of the gtt mapping in the fence
+		 * reg, so dont bother to check the size */
+		if (stride / 128 > I965_FENCE_MAX_PITCH_VAL)
+			return false;
+	} else if (IS_I9XX(dev)) {
+		if (stride / tile_width > I830_FENCE_MAX_PITCH_VAL ||
+		    size > (I830_FENCE_MAX_SIZE_VAL << 20))
+			return false;
+	} else {
+		if (stride / 128 > I830_FENCE_MAX_PITCH_VAL ||
+		    size > (I830_FENCE_MAX_SIZE_VAL << 19))
+			return false;
+	}
+
 	/* 965+ just needs multiples of tile width */
 	if (IS_I965G(dev)) {
 		if (stride & (tile_width - 1))