title: Erasing Flash NOR: ioctl(MEMUNLOCK) return status?
body: <p>I'm trying to erase a NOR Flash memory with Linux MTD driver in C...</p>
  
  <p>I'm confused about the return status from the <code>ioctl(MEMUNLOCK)</code> call which returns an error even if <code>ioctl(MEMERASE)</code> is successful after it.</p>
  
  <p>The following code displays the warning message but works (i.e. the Flash block has been erased):</p>
  
  <pre class="lang-c prettyprint-override"><code>int erase_MTD_Pages(int fd, size_t size, off_t offset)
  {
      mtd_info_t   mtd_info;
      erase_info_t ei;
  
      ioctl(fd, MEMGETINFO, &amp;mtd_info);
      ei.length = mtd_info.erasesize;
  
      for(ei.start = offset; ei.start &lt; (offset+size); ei.start += mtd_info.erasesize) {
          if(ioctl(fd, MEMUNLOCK, &amp;ei) &lt; 0)
          {
  //          logPrintf(FAILURE, "[Flash] Can not unlock MTD (MEMUNLOCK, errno=%d)!\n", errno);
  //          return RETURN_FILE_ERROR;
              logPrintf(WARNING, "[Flash] Can not unlock MTD (MEMUNLOCK, errno=%d)!\n", errno);
  
          }
          if(ioctl(fd, MEMERASE, &amp;ei) &lt; 0)
          {
              logPrintf(FAILURE, "[Flash] Can not erase MTD (MEMERASE, errno=%d)!\n", errno);
              return RETURN_FILE_ERROR;
          }
      }
      return RETURN_SUCCESS;
  }
  </code></pre>
  
  <p>When I look some C codes on the net, the return status from MEMUNLOCK is not always checked (e.g. from <a href="https://aachen.uni-dsl.de/svn/unidsl_firmware/wr0.9pc/trunk/buildroot/package/mtd/mtd.c" rel="noreferrer">mtc.c</a>):</p>
  
  <pre class="lang-c prettyprint-override"><code>ioctl(fd, MEMUNLOCK, &amp;mtdEraseInfo);
  if(ioctl(fd, MEMERASE, &amp;mtdEraseInfo)) {
      fprintf(stderr, "Could not erase MTD device: %s\n", mtd);
      close(fd);
      exit(1);
  }
  </code></pre>
  
  <p><code>flash_unlock</code> also returns an error:</p>
  
  <pre><code>root $ cat /proc/mtd
  dev:    size   erasesize  name
  mtd0: 00020000 00020000 "X-Loader-NOR"
  mtd1: 000a0000 00020000 "U-Boot-NOR"
  mtd2: 00040000 00020000 "Boot Env-NOR"
  mtd3: 00400000 00020000 "Kernel-NOR"
  mtd4: 03b00000 00020000 "File System-NOR"
  
  root $ mtd_debug info /dev/mtd3
  mtd.type = MTD_NORFLASH
  mtd.flags = MTD_CAP_NORFLASH
  mtd.size = 4194304 (4M)
  mtd.erasesize = 131072 (128K)
  mtd.writesize = 1
  mtd.oobsize = 0
  regions = 0
  
  root $ flash_unlock /dev/mtd3
  Could not unlock MTD device: /dev/mtd3
  </code></pre>
  
  <p>Am I missing something? Is it normal to get an error from MEMUNLOCK with some configurations?</p>
  
  <p>Notes / Environment:</p>
  
  <ul>
  <li>The read-only flag (MTD_WRITEABLE) in <strong>not</strong> set on the <code>mtd3</code> partition (only on <code>mtd0</code> and <code>mtd1</code>).</li>
  <li><code>flash_lock</code> also returns the same error.</li>
  <li>TI AM3505 (ARM Cortex A8, OMAP34).</li>
  <li>Linux 2.6.37.</li>
  <li>Flash NOR Spansion S29GL512S12DHIV1.</li>
  </ul>
  
  <p>Kernel log:</p>
  
  <pre><code>mtdoops: mtd device (mtddev=name/number) must be supplied
  physmap platform flash device: 08000000 at 08000000
  physmap-flash.0: Found 1 x16 devices at 0x0 in 16-bit bank. Manufacturer ID 0x000001 Chip ID 0x002301
  Amd/Fujitsu Extended Query Table at 0x0040
    Amd/Fujitsu Extended Query version 1.5.
    Silicon revision: 14
    Address sensitive unlock: Required
    Erase Suspend: Read/write
    Block protection: 1 sectors per group
    Temporary block unprotect: Not supported
    Block protect/unprotect scheme: 8
    Number of simultaneous operations: 0
    Burst mode: Not supported
    Page mode: 12 word page
    Vpp Supply Minimum Program/Erase Voltage: 0.0 V
    Vpp Supply Maximum Program/Erase Voltage: 0.0 V
    Top/Bottom Boot Block: Uniform, Top WP
  number of CFI chips: 1
  RedBoot partition parsing not available
  Using physmap partition information
  Creating 5 MTD partitions on "physmap-flash.0":
  0x000000000000-0x000000020000 : "X-Loader-NOR"
  0x000000020000-0x0000000c0000 : "U-Boot-NOR"
  0x0000000c0000-0x000000100000 : "Boot Env-NOR"
  0x000000100000-0x000000500000 : "Kernel-NOR"
  0x000000500000-0x000004000000 : "File System-NOR"
  </code></pre>