johnlanglois on "How to Check cart for Simple Product"

In WooCommerce 2.0.12 I have a filter, add_filter( 'woocommerce_add_to_cart_validation), that does not need to run if the product being added is a simple product.

Is there a variable I could check or a function call that would let me know that the product being added is a simple product so that I could just return?

Thanks