drm/915: fix relaxed tiling on gen2: tile height

A tile on gen2 has a size of 2kb, stride of 128 bytes and 16 rows.

Userspace was broken and assumed 8 rows. Chris Wilson noted that the
kernel unfortunately can't reliable check that because libdrm rounds
up the size to the next bucket.
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NKeith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -1449,8 +1449,9 @@ i915_gem_get_unfenced_gtt_alignment(struct drm_i915_gem_object *obj)
 	 * edge of an even tile row (where tile rows are counted as if the bo is
 	 * placed in a fenced gtt region).
 	 */
-	if (IS_GEN2(dev) ||
-	    (obj->tiling_mode == I915_TILING_Y && HAS_128_BYTE_Y_TILING(dev)))
+	if (IS_GEN2(dev))
+		tile_height = 16;
+	else if (obj->tiling_mode == I915_TILING_Y && HAS_128_BYTE_Y_TILING(dev))
 		tile_height = 32;
 	else
 		tile_height = 8;