Hi Mathangi,
Can you try the below piece of code in your get_p method of your text attribute and check about the length.
CASE iv_property.
WHEN if_bsp_wd_model_setter_getter=>fp_fieldtype.
rv_value = cl_bsp_dlc_view_descriptor=>FIELD_TYPE_TEXTAREA.
ENDCASE.
Regards,
Dharmakasi.