drm/i915: Rebind the buffer if its alignment constraints changes with tiling

Early gen3 and gen2 chipset do not have the relaxed per-surface tiling
constraints of the later chipsets, so we need to check that the GTT
alignment is correct for the new tiling. If it is not, we need to
rebind.

Reported-by: Daniel Vetter <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>

drivers/gpu/drm/i915/i915_drv.h

···
 void i915_gem_free_all_phys_object(struct drm_device *dev);
 void i915_gem_release(struct drm_device *dev, struct drm_file *file);
 
+uint32_t
+i915_gem_get_unfenced_gtt_alignment(struct drm_i915_gem_object *obj);
+
 /* i915_gem_gtt.c */
 void i915_gem_restore_gtt_mappings(struct drm_device *dev);
 int __must_check i915_gem_gtt_bind_object(struct drm_i915_gem_object *obj);

drivers/gpu/drm/i915/i915_gem.c

···
  * Return the required GTT alignment for an object, only taking into account
  * unfenced tiled surface requirements.
  */
-static uint32_t
+uint32_t
 i915_gem_get_unfenced_gtt_alignment(struct drm_i915_gem_object *obj)
 {
 	struct drm_device *dev = obj->base.dev;

drivers/gpu/drm/i915/i915_gem_tiling.c

···
 			(obj->gtt_offset + obj->base.size <= dev_priv->mm.gtt_mappable_end &&
 			 i915_gem_object_fence_ok(obj, args->tiling_mode));
 
-		obj->tiling_changed = true;
-		obj->tiling_mode = args->tiling_mode;
-		obj->stride = args->stride;
+		/* Rebind if we need a change of alignment */
+		if (!obj->map_and_fenceable) {
+			u32 unfenced_alignment =
+				i915_gem_get_unfenced_gtt_alignment(obj);
+			if (obj->gtt_offset & (unfenced_alignment - 1))
+				ret = i915_gem_object_unbind(obj);
+		}
+
+		if (ret == 0) {
+			obj->tiling_changed = true;
+			obj->tiling_mode = args->tiling_mode;
+			obj->stride = args->stride;
+		}
 	}
+	/* we have to maintain this existing ABI... */
+	args->stride = obj->stride;
+	args->tiling_mode = obj->tiling_mode;
 	drm_gem_object_unreference(&obj->base);
 	mutex_unlock(&dev->struct_mutex);
 
-	return 0;
+	return ret;
 }
 
 /**