Drupal Commerce Get all known product displays

commerce_get_product_display_bundles.php

<?php
/**
 * Get all known product displays.
 *
 * We know they are product displays if they are node and have
 *   commerce_product_reference field type.
 *
 * @return array
 *   Array of bundle.
 */
function _commerce_get_product_display_bundles() {
  $target_bundles = &drupal_static(__FUNCTION__);

  if (!isset($target_bundles)) {
    $target_bundles = array();

    $fields = field_info_fields();
    foreach ($fields as $field) {
      if ($field['type'] == 'commerce_product_reference' && isset($field['bundles']) && isset($field['bundles']['node'])) {
        $target_bundles = array_merge($target_bundles, drupal_map_assoc($field['bundles']['node']));
      }
    }
  }

  return $target_bundles;

}