See the Advanced Actions section of the Plugin API/Action Reference article.
The hook allows meta box registration for any post type.
Passes two parameters: $post_type and $post.
Note: You can also use add_meta_boxes_{post_type} for best practice, so your hook will only run when editing a specific post type. This will only receive 1 parameter - $post.
function adding_custom_meta_boxes( $post_type, $post ) {
add_meta_box(
'my-meta-box',
__( 'My Meta Box' ),
'render_my_meta_box',
'post',
'normal',
'default'
);
}
add_action( 'add_meta_boxes', 'adding_custom_meta_boxes', 10, 2 );
Now for a post-type specific call.
function adding_custom_meta_boxes( $post ) {
add_meta_box(
'my-meta-box',
__( 'My Meta Box' ),
'render_my_meta_box',
'post',
'normal',
'default'
);
}
add_action( 'add_meta_boxes_post', 'adding_custom_meta_boxes' );
Both will accomplish the same thing. Best practice is to use add_meta_boxes_{post-type} to create less unnecessary hooks for other post types.