WordPress: loop shortcode for pages

wp_functions_loopShortcode.php

// --------------------------------------------------
// ---------- Create custom loop shortcode ----------
// --------------------------------------------------
// usage: [loop cat="17" posts_per_page="6" ]
// --------------------------------------------------
<?php
    add_shortcode('loop', 'shortcode_query');

    function shortcode_query($atts, $content){
        extract(shortcode_atts(array( // a few default values. more query params at http://codex.wordpress.org/Class_Reference/WP_Query
            'posts_per_page'   => 4,
            'caller_get_posts' => 1,
            'post__not_in'     => get_option('sticky_posts'),
        ), $atts));

        global $post;

        $posts = new WP_Query($atts);
        $output = '';
        if ($posts->have_posts())
        while ($posts->have_posts()):
            $posts->the_post();
        ?>

            <article <?php post_class() ?>>
                <footer class="entry-meta">
                    <time datetime="<?php echo date(DATE_W3C); ?>" pubdate class="updated"><?php the_time('F jS, Y') ?></time>
                    <small>in <?php the_category(', ') ?></small>
                </footer>
                
                <?php if ( has_post_thumbnail()) : ?>
                    
                    <a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>" class="" >
                        <?php echo clean_img_width_height(get_the_post_thumbnail(get_the_ID())); ?>
                    </a>
                
                <?php endif; ?>
                
                <h2><a href="<?php the_permalink() ?>"><?php the_title(); ?></a></h2>
                <p><?php the_excerpt(); ?></p>
            </article>

        <?php
        endwhile;
        else
        return; // no posts found

        wp_reset_query();
        return html_entity_decode($output);
    }
?>