ACF < v5 Get Parent Block Data in Inner Block Template

// Get parent block data
function get_parent_block_data($needle, $haystacks, $name, &$block_data = array()) {
  foreach ($haystacks as $haystack) {
    if (!empty($haystack['attrs']['id']) && $haystack['attrs']['id'] == $needle) {
      return $block_data;
    }
  }

  foreach ($haystacks as $haystack)  {
    if (!empty($haystack['innerBlocks']) && $haystack['blockName'] !== $name) {

      $block_data = array();
      foreach ($haystack['attrs']['data'] as $key => $value) {
        if (substr($key, 0, 1) !== '_') {
          $block_data[$key] = $value;
        }
      }
      get_parent_block_data($needle, $haystack['innerBlocks'], $name, $block_data);
    } else if (!empty($haystack['innerBlocks'])) {
      get_parent_block_data($needle, $haystack['innerBlocks'], $name, $block_data);
    }
  }
}

function get_parent_block($id, $name) {
  $blocks = parse_blocks(get_post()->post_content);
  get_parent_block_data($id, $blocks, $name, $block_data);
  return $block_data;
}

// Usage inside innerblock template
$parent = get_parent_block(block['id'], block['name']);
print_r($parent['FIELD_NAME']);