Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934726AbdC3TzB (ORCPT ); Thu, 30 Mar 2017 15:55:01 -0400 Received: from mail-wr0-f196.google.com ([209.85.128.196]:34051 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934152AbdC3TzA (ORCPT ); Thu, 30 Mar 2017 15:55:00 -0400 From: Nicolai Stange To: Martin Schwidefsky , Heiko Carstens Cc: John Stultz , linux-kernel@vger.kernel.org, Nicolai Stange , David Hildenbrand , linux-s390@vger.kernel.org Subject: [PATCH] s390/time: set ->min_delta_ticks and ->max_delta_ticks Date: Thu, 30 Mar 2017 21:54:55 +0200 Message-Id: <20170330195455.7393-1-nicstange@gmail.com> X-Mailer: git-send-email 2.12.0 In-Reply-To: <20170326134403.16226-1-nicstange@gmail.com> References: <20170326134403.16226-1-nicstange@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2692 Lines: 76 In preparation for making the clockevents core NTP correction aware, all clockevent device drivers must set ->min_delta_ticks and ->max_delta_ticks rather than ->min_delta_ns and ->max_delta_ns: a clockevent device's rate is going to change dynamically and thus, the ratio of ns to ticks ceases to stay invariant. Currently, the s390's CPU timer clockevent device is initialized as follows: cd->min_delta_ns = 1; cd->max_delta_ns = LONG_MAX; Note that the device's time to cycle conversion factor, i.e. cd->mult / (2^cd->shift), is approx. equal to 4. Hence, this would translate to cd->min_delta_ticks = 4; cd->max_delta_ticks = 4 * LONG_MAX; However, a minimum value of 1ns is in the range of noise anyway and the clockevent core will take care of this by increasing it to 1us or so. Furthermore, 4*LONG_MAX would overflow the unsigned long argument the clockevent devices gets programmed with. Thus, initialize ->min_delta_ticks with 1 and ->max_delta_ticks with ULONG_MAX. This patch alone doesn't introduce any change in functionality as the clockevents core still looks exclusively at the (untouched) ->min_delta_ns and ->max_delta_ns. As soon as this has changed, a followup patch will purge the initialization of ->min_delta_ns and ->max_delta_ns from this driver. Signed-off-by: Nicolai Stange --- Notes: This prerequisite patch is part of a larger effort to feed NTP corrections into the clockevent devices' frequencies and thus avoiding their notion of time to diverge from the system's one. If you're interested, the current state of the whole series can be found at [1]. If you haven't got any objections and these prerequisites get merged by 4.12 everywhere, I'll proceed with the remainder of this series in 4.13. Applicable to next-20170324 as well as to John' Stultz tree [2]. [1] git://nicst.de/linux.git cev-freq-adj.v10.fortglx-4.12-time https://nicst.de/git/?p=linux.git;a=shortlog;h=refs/heads/cev-freq-adj.v10.fortglx-4.12-time [2] https://git.linaro.org/people/john.stultz/linux.git fortglx/4.12/time arch/s390/kernel/time.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c index c31da46bc037..c3a52f9a69a0 100644 --- a/arch/s390/kernel/time.c +++ b/arch/s390/kernel/time.c @@ -158,7 +158,9 @@ void init_cpu_timer(void) cd->mult = 16777; cd->shift = 12; cd->min_delta_ns = 1; + cd->min_delta_ticks = 1; cd->max_delta_ns = LONG_MAX; + cd->max_delta_ticks = ULONG_MAX; cd->rating = 400; cd->cpumask = cpumask_of(cpu); cd->set_next_event = s390_next_event; -- 2.12.0