All grounds for relief available to an applicant under this chapter must be raised in the applicant's original, supplemental or amended application. Any ground finally adjudicated or not raised, or knowingly, voluntarily, and intelligently waived in the proceeding that resulted in the conviction or sentence, or in any other proceeding the applicant has taken to secure relief, may not be the basis for a subsequent application, unless the court finds a ground for relief asserted which for sufficient reason was not asserted or was inadequately raised in the original, supplemental, or amended application.
Iowa Code § 822.8