More specific provisions:

Art. 6 II: "Member States may maintain or introduce more specific provisions [...] with regard to processing for compliance with points (c) and (e) of paragraph 1 by determining more precisely specific requirements [...] including for other specific processing situations as provided for in Chapter IX." ► Art. 90 is in Chapter IX.

Reconciling:

Art. 90 I 1: "Member States may adopt specific rules to set out the powers of the supervisory authorities [...  ]that are subject, under Union or Member State law or rules established by national competent bodies, to an obligation of professional secrecy or other equivalent obligations of secrecy where this is necessary and proportionate to reconcile the right of the protection of personal data with the obligation of secrecy."