Sub-site logo points to the sub-site's home page by default...and the requirement is to point it to the top level site's.
Solution:
We can not change Master Page in Office365/SharePoint Online site so we need to embed/inject the following JavaScript:
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script language="javascript" type="text/javascript">
$(document).ready(function () {
$('#ctl00_onetidProjectPropertyTitleGraphic').attr('href','/sites/Portal');
$('#ctl00_onetidProjectPropertyTitleGraphic').removeAttr('id');
});
</script>
