From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753131AbcJKAq7 (ORCPT ); Mon, 10 Oct 2016 20:46:59 -0400 Received: from mail-pf0-f177.google.com ([209.85.192.177]:34269 "EHLO mail-pf0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753063AbcJKAqy (ORCPT ); Mon, 10 Oct 2016 20:46:54 -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: <53745281-AF17-4A3A-8BB5-63EED3563298@gmail.com> Date: Tue, 11 Oct 2016 09:46:49 +0900 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 , kgene.kim@samsung.com Message-Id: <50A42280-0A39-44E3-8E35-C24031EB4DF0@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> <53745281-AF17-4A3A-8BB5-63EED3563298@gmail.com> 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 u9B0lAqJ005166 2016. 10. 3. 21:19 Kukjin Kim wrote: + my samsung email > 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