I am upgrading the kernel version from 4.14 to 5.4.103.

We have /dev/pmem0 created with the following command line: memmap=0x1000000!0x10000000

As a result /dev/pmem0 has been created. But, the mount command is failing with errors.

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

Can someone tell me whether something got changed with 5.4.x kernel version?

PS: If I remove the 'dax' option, mount becomes successful.