Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753123AbcJCMUD (ORCPT ); Mon, 3 Oct 2016 08:20:03 -0400 Received: from mail-pa0-f54.google.com ([209.85.220.54]:33575 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751479AbcJCMTy (ORCPT ); Mon, 3 Oct 2016 08:19:54 -0400 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (1.0) Subject: Re: [GIT PULL 1/3] ARM: soc: exynos: Drivers for v4.9 From: Kukjin Kim X-Mailer: iPhone Mail (14A456) In-Reply-To: <20161003074825.GA2724@kozik-lap> Date: Mon, 3 Oct 2016 20:19:48 +0800 Cc: Olof Johansson , Arnd Bergmann , Kevin Hilman , "arm@kernel.org" , Krzysztof Kozlowski , Kukjin Kim , "linux-arm-kernel@lists.infradead.org" , "linux-samsung-soc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Bartlomiej Zolnierkiewicz , Javier Martinez Canillas , Daniel Lezcano Message-Id: <53745281-AF17-4A3A-8BB5-63EED3563298@gmail.com> References: <1474216788-17282-1-git-send-email-krzk@kernel.org> <1474216788-17282-2-git-send-email-krzk@kernel.org> <2663426.T8oUku18qe@wuerfel> <20160919155302.GA4447@kozik-book> <20161003074825.GA2724@kozik-lap> To: Krzysztof Kozlowski Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id u93CK7Un002582 Content-Length: 3085 Lines: 62 2016. 10. 3. 15:48 Krzysztof Kozlowski wrote: >> On Sun, Oct 02, 2016 at 05:25:07PM -0700, Olof Johansson wrote: >>> On Mon, Sep 19, 2016 at 8:53 AM, Krzysztof Kozlowski wrote: >>>> On Mon, Sep 19, 2016 at 05:02:40PM +0200, Arnd Bergmann wrote: >>>>> On Sunday, September 18, 2016 6:39:46 PM CEST Krzysztof Kozlowski wrote: >>>>> Samsung drivers/soc update for v4.9: >>>>> 1. Allow compile testing of exynos-mct clocksource driver on ARM64. >>>>> 2. Document Exynos5433 PMU compatible (already used by clkout driver and more >>>>> will be coming soon). >>>> >>>> Pulled into next/drivers, thanks >>>> >>>> Just for my understanding: why do we need the exynos-mct driver on ARM64 >>>> but not the delay-timer portion of it? >>> >>> I think we want all of it but Doug's optimization 3252a646aa2c >>> ("clocksource: exynos_mct: Only use 32-bits where possible") is not >>> ARM64 friendly. One way of dealing with it would be to prepare two >>> versions of exynos4_read_current_timer(). One reading only lower 32-bit >>> value for ARMv7 and second (slow) reading lower and upper for ARMv8. >>> >>>> >>>> Is there an advantage in using MCT over the architected timer on these >>>> chips? If so, should we also have a way to use it as the delay timer? >>> >>> No, there is no real advantage... except that the SoC has some >>> interesting "characteristics"... The timers are tightly coupled. Very >>> tightly. I spent a lot of time and failed to boot my ARMv8 board without >>> some MCT magic. >> >> What kind of magic is that? > > Most notably: the arch timer starts when MCT forward running counter > starts. Without kicking MCT, the arch timer seems to be frozen. > >> I can understand that needing the MCT for >> some system-level timer functionality might be true (wakeups, etc), >> but for system timesource avoiding the MMIO timer and using the arch >> ones is a substantial performance improvement for gettimeofday() and >> friends. >> >> There was extensive discussion last year over using arch timers on >> 5420/5422, and it fizzled out with vague comments about something not >> working right between A15/A7 on b.L. hardware. I'm presuming whatever >> implementation details of that SoC has since been fixed on later chips >> (including v8). Any chance you can confirm? It'd be very nice to leave >> MCT behind on v8 as a system time source. > > Unfortunately, I cannot confirm this, at least on Exynos5433 (ARMv8). I > played with arch and MCT timers on it and failed to get the > arch-timer-only setup working. I did not have access to newer Exynos > designs (Exynos 7) so I do not know how it works there. Hi guys, I know what Olof want to know and actually several days ago someone asked me about that. As you guys talked, a couple of years ago there were some discussions...BTW I need to contact to hardware designer before let you guys know because something needs to be confirmed by them even I know roughly. Note I'm in vacation with my family. Will be back on this in several days with exact information. BRs, Kukjin