Have upgraded HDLC version for 2.4.20 kernel from 1.02 to 1.14.
And recompiled the kernel and HDLC driver.
Also it requires sethdlc utility for configuring HDLC and driver parameters which was found on the internet where the patch for HDLC was found.
Having done that with kernel and driver reloded, when you try to configure HDLC interface for HDLC and physical parameters as follows:

#sethdlc hdlc0 hdlc nrzi no-parity

error is thrown

hdlc0: Unable to set HDLC protocol information: Operation not supported.

Currently the driver doesnt support configuration of physical parameter.

But can you configure the HDLC protocol parameters for the interface having modified the HDLC version in the kernel 2.4.20.
Any support will be highly appriciated.
Thanks in advance.