Place for favicon

I´ve read through some topics of using a favicon in the twenty twelve theme. I´ve put the code below in function file. Put the favicon image named favicon.ico both in theme folder and in root of the site. Still doesn´t function. Any ideas?

function favicon_link() {
    echo '<link rel="shortcut icon" type="image/x-icon" href="/favicon.ico" />' . "\n";
}
add_action( 'wp_head', 'favicon_link' );