When a defendant knowingly and intelligently waives jail-time custody credits in order to be placed on probation, the waiver applies to any future use of such credits, including a prison sentence following a later violation of probation. At the time of his original plea, the defendant signed a waiver in which he agreed to waive all credits for jail time served up to that point, pursuant to People v. Johnson (1978) 82 Cal.App.3rd 183. Following a violation of probation, the defendant was reinstated on probation on condition of serving an additional 90 days in county jail; he again entered a Johnson waiver, and this time was expressly advised that the waiver would apply to any future prison sentence that might be imposed. On appeal after he was later sentenced to prison, the defendant argued that he was entitled the credits earned up to the point of the first Johnson waiver. The Court of Appeal held that the waiver of time credits was not knowing and intelligent because there was no explicit advisement that the waiver would apply to the state prison sentence if appellants probation were later revoked. The Supreme Court reversed, finding the waiver to be knowing and intelligent, and holding that when a defendant so waives jail-time custody credits, the waiver applies to any future use of such credits should the court later revoke probation and sentence the defendant to prison. The court found nothing in the original plea hearing to suggest that the waiver was anything other than a full relinquishment of the statutory right to section 2900.5 credits for all purposes.