drm/i915: Limit fb x offset due to fences

If there's a fence on the object it will be aligned to the start
of the object, and hence CPU rendering to any fb that straddles
the fence edge will come out wrong due to lines wrapping at the
wrong place.

We have no API to manage fences on a sub-object level, so we can't
really fix this in any way. Additonally gen2/3 fences are rather
coarse grained so adjusting the offset migth not even be possible.

Avoid these problems by requiring the fb layout to agree with the
fence layout (if present).

v2: Rebase due to i915_gem_object_get_tiling() & co.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470821001-25272-8-git-send-email-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -2472,6 +2472,22 @@ intel_fill_fb_info(struct drm_i915_private *dev_priv,
 
 		intel_fb_offset_to_xy(&x, &y, fb, i);
 
+		/*
+		 * The fence (if used) is aligned to the start of the object
+		 * so having the framebuffer wrap around across the edge of the
+		 * fenced region doesn't really work. We have no API to configure
+		 * the fence start offset within the object (nor could we probably
+		 * on gen2/3). So it's just easier if we just require that the
+		 * fb layout agrees with the fence layout. We already check that the
+		 * fb stride matches the fence stride elsewhere.
+		 */
+		if (i915_gem_object_is_tiled(intel_fb->obj) &&
+		    (x + width) * cpp > fb->pitches[i]) {
+			DRM_DEBUG("bad fb plane %d offset: 0x%x\n",
+				  i, fb->offsets[i]);
+			return -EINVAL;
+		}
+
 		/*
 		 * First pixel of the framebuffer from
 		 * the start of the normal gtt mapping.