Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753318AbbG1PY3 (ORCPT ); Tue, 28 Jul 2015 11:24:29 -0400 Received: from mail-wi0-f171.google.com ([209.85.212.171]:34598 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751785AbbG1PY1 (ORCPT ); Tue, 28 Jul 2015 11:24:27 -0400 MIME-Version: 1.0 In-Reply-To: <1438032507.17734.46.camel@gmail.com> References: <1438032507.17734.46.camel@gmail.com> Date: Tue, 28 Jul 2015 08:24:26 -0700 X-Google-Sender-Auth: 8KFmXbhr2_tynNmBP642oRAFVyk Message-ID: Subject: Re: [RFC PATCH 0/3] clocksource: exynos_mct: allow mct to use 64-bit counter from coprocessor From: Doug Anderson To: Alexey Klimov Cc: linux-samsung-soc , Daniel Lezcano , Chirantan Ekbote , t.dakhran@gmail.com, =?UTF-8?Q?Krzysztof_Koz=C5=82owski?= , kgene , Thomas Gleixner , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , yury.norov@gmail.com, Alim Akhtar Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1653 Lines: 41 Alexey, On Mon, Jul 27, 2015 at 2:28 PM, Alexey Klimov wrote: > Hi all, > > year(s) ago it was discovered that MCT timer and ARM architectured > timer > are the same hardware with different interface. Here [1]. > > I followed mail-list discussions about removing MCT and using arch > timer for Exynos5-based SoCs but things aren't moving at least latest > upstream kernel on odroid-xu3 will use MCT as default timers. > Maybe the reason are some power-management related things that very > specific to Samsung. I don't know. > > > Idea of this draft patchset comes from Doug patches when he tried to > optimize read of 64-bit counter located in mmio. [2] > Why not using cp15 counter instead if possible? I hate to burst your bubble here, but... ...I think it would be a bad idea to use the cp15 counter on exynos 5422. According to Samsung, there are issues where using cp15 could sometimes return the wrong value, especially if you happen to read it while on an A7 instead of an A15. It will tend to work pretty well, but Samsung claimed that it might not work right on some CPUs or at some temperatures. I've added Alim who provided this information to me (in the private http://crosbug.com/p/29556). He may be able to elaborate more. Generally I'd say that if the arch timer works for you: use the arch timer. If the arch timer doesn't work for you, use the MCT. -Doug -- 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/