Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751428AbaKFSOv (ORCPT ); Thu, 6 Nov 2014 13:14:51 -0500 Received: from mail-vc0-f177.google.com ([209.85.220.177]:33764 "EHLO mail-vc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750970AbaKFSOu (ORCPT ); Thu, 6 Nov 2014 13:14:50 -0500 MIME-Version: 1.0 In-Reply-To: References: <1415296639-40203-1-git-send-email-anatol.pomozov@gmail.com> Date: Thu, 6 Nov 2014 10:14:49 -0800 Message-ID: Subject: Re: [PATCH] clocksource: arch_timer: Mark ARMv8 system timer as 'always-on' From: Anatol Pomozov To: Marc Zyngier Cc: daniel.lezcano@linaro.org, lorenzo.pieralisi@arm.com, tglx@linutronix.de, LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi On Thu, Nov 6, 2014 at 10:09 AM, Marc Zyngier wrote: > Hi Anatol, > > On 2014-11-06 17:57, Anatol Pomozov wrote: >> >> Quoting ARMv8 Reference Manual section D6.1: >> "The system counter must be implemented in an always-on power domain." > > > Yes. And the key words here are "system counter". That's the global counter, > not the per-cpu view of that, and critically nor comparators. > > The timers (per-cpu counter+comparator) will happily go down with the CPU, > and won't be able to wake it up. Exactly like ARMv7, by the way. > >> There is no need to keep 'always-on' configurable on ARMv8. We ignore >> this dts property value and unconditionally set it to true. >> >> The issue was discovered while working on ARMv8 board with only one timer >> (arm arch timer). If 'always-on' is false then it disables high-resolution >> timer functionality. > > > Yup, and that's by design (see above). The *only* case where it is really > "always-on" is when a virtual machine is running (if the vcpu is running > then the physical CPU is, and so is the timer). > > If your system really never does any form of PM, then fine, just put the DT > property in. Removing it is, I'm sorry to say, a bit short sighted. Thanks for the clarification Marc. I will look if it possible to get the other (always-on) timer back. Ignore my patch. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/