Getting field value that attached to Commerce product field
You should be able to use entity_metadata_wrapper quite nicely for this. Note that it is part of the Entity API, but that is a dependency of Drupal Commerce so you'll be fine in this case.

Something like the following code should do it:

$wrapper = entity_metadata_wrapper('commerce_product', YOUR-REQUIRED-PRODUCT-ID);

$discount = $wrapper-&gt;field_diskon-&gt;value();


You can find out more about how to use entity_metadata_wrapper() here.