title: Unable to mount /dev/pmem0 with 'dax' option
body: <p>I am upgrading the kernel version from 4.14 to 5.4.103.</p>
  <p>We have /dev/pmem0 created with the following command line:  memmap=0x1000000!0x10000000</p>
  <p>As a result /dev/pmem0 has been created. But, the mount command is failing with errors.</p>
  <pre><code>mount -o dax /dev/pmem0 /mnt/data1
  
  [   28.920384] squashfs: Unknown parameter 'dax'
  [   28.945516] EXT4-fs (pmem0): DAX unsupported by block device.
  [   28.951523] squashfs: Unknown parameter 'dax'
    mount: mounting /dev/pmem0 on /mnt/data1 failed: Invalid argument
  </code></pre>
  <p>Can someone tell me whether something got changed with 5.4.x kernel version?</p>
  <p>PS: If I remove the 'dax' option, mount becomes successful.</p>