drm/vmwgfx: fix lock breakage

After:

commit d059f652e73c35678d28d4cd09ab2cec89696af9
Author:     Daniel Vetter <daniel.vetter@ffwll.ch>
AuthorDate: Fri Jul 25 18:07:40 2014 +0200

    drm: Handle legacy per-crtc locking with full acquire ctx

drm_mode_cursor_common() was switched to use drm_modeset_(un)lock_crtc()
which uses full aquire ctx.  So dropping/reaquiring the lock via
drm_modeset_(un)lock() directly isn't the right thing to do, as lockdep
kindly points out.

The 'FIXME's about sorting out whether vmwgfx *really* needs to lock-all
for cursor updates still apply.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Tested-by: Thomas Hellstrom <thellstrom@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_kms.c

@@ -187,7 +187,7 @@ int vmw_du_crtc_cursor_set(struct drm_crtc *crtc, struct drm_file *file_priv,
 	 * can do this since the caller in the drm core doesn't check anything
 	 * which is protected by any looks.
 	 */
-	drm_modeset_unlock(&crtc->mutex);
+	drm_modeset_unlock_crtc(crtc);
 	drm_modeset_lock_all(dev_priv->dev);
 
 	/* A lot of the code assumes this */
@@ -252,7 +252,7 @@ int vmw_du_crtc_cursor_set(struct drm_crtc *crtc, struct drm_file *file_priv,
 	ret = 0;
 out:
 	drm_modeset_unlock_all(dev_priv->dev);
-	drm_modeset_lock(&crtc->mutex, NULL);
+	drm_modeset_lock_crtc(crtc);
 
 	return ret;
 }
@@ -273,7 +273,7 @@ int vmw_du_crtc_cursor_move(struct drm_crtc *crtc, int x, int y)
 	 * can do this since the caller in the drm core doesn't check anything
 	 * which is protected by any looks.
 	 */
-	drm_modeset_unlock(&crtc->mutex);
+	drm_modeset_unlock_crtc(crtc);
 	drm_modeset_lock_all(dev_priv->dev);
 
 	vmw_cursor_update_position(dev_priv, shown,
@@ -281,7 +281,7 @@ int vmw_du_crtc_cursor_move(struct drm_crtc *crtc, int x, int y)
 				   du->cursor_y + du->hotspot_y);
 
 	drm_modeset_unlock_all(dev_priv->dev);
-	drm_modeset_lock(&crtc->mutex, NULL);
+	drm_modeset_lock_crtc(crtc);
 
 	return 0;
 }