Attaching comments to blog post promoted to front page
The reason you do not see comment form on content promoted to front page is because by default comment form shows on full node view.So following code may help you.

function mymodulename_node_view($node, $view_mode, $langcode) {
  if(drupal_is_front_page() &amp;&amp; $node-&gt;type == "your_content_type") {
      $node-&gt;content['comments'] = comment_node_page_additions($node);
  } 
}