cara memasukkan hasil penjumlahan ke dalam textfield

//input pesanan
<?php echo form_open_multipart('admin/opesan'); ?>
<td><select name="no_meja" class="form-control">
  <option>Pilih No.Meja</option>
  <option value="1">1</option>
  <option value="2">2</option>
  <option value="3">3</option>
  <option value="4">4</option>
  <option value="5">5</option>
  <option value="6">6</option>
  <option value="7">7</option>
  <option value="8">8</option>
  <option value="9">9</option>
  <option value="10">10</option>
</select></td>

<td><input type="date" name="tgl_order" required></td>
//permasalahannya di subtotal_val
<td><input type="text" name="total" class="subtotal_val" readonly></td>
<td><button type="submit" onClick="return confirm('apakah anda sudah selesai menginput menu?')">Selesai</button></td></tr>
<h4></h4>
</tbody></table><br/>
// hasil data tabel detail pesanan
<h3 class="text-center">Data Pesanan</h3>
<div style="overflow-y: scroll; width: 100%"><table id="example4" class="table table-bordered table-hover table-striped" style="width: 100%">
  <thead>

    <th>ID Produk</th>
    <th>Nama Pesanan</th>
    <th>Harga Satuan</th>
    <th>Jumlah Porsi</th>
    <th>Subtotal</th>
    <th>Aksi</th>
  </thead>
  <tbody>
     <?php
     $no = 1;
     $total = 0;
     foreach ($detail->result() as $row => $r) {

     ?>
    <tr>

      <td><?php echo $r->id_menu; ?></td>
      <td><?php echo $r->nama_pesanan; ?></td>
      <td id="harga_satuan" class="harga_satuan">Rp.<?php echo $r->harga_satuan; ?></td>
      <td id="jml_porsi" class="jml_porsi" onkeyup="total()"><?php echo $r->jml_porsi; ?></td>
      <td id="subtotal" class="subtotal" onkeyup="total()">Rp.<?php echo $r->subtotal; ?></td>
      <td><a href="<?php echo site_url('admin/hapus2/').$r->id_menu?>"
            onClick="return confirm('apakah anda yakin ingin menghapus pesanan?')"><button>Hapus</button></a></td></tr>
       <?php
        $total +=$r->subtotal;
     }

        ?>
// grand total
       <tr style="font-weight: bold;"><td colspan="3"></td><td>Total :</td><td id="total1" name="total1" class="total1">Rp.<?php echo $total; ?></td></tr>


  </tbody></table><br/>