Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932564Ab3IMNKE (ORCPT ); Fri, 13 Sep 2013 09:10:04 -0400 Received: from mail-bk0-f42.google.com ([209.85.214.42]:58852 "EHLO mail-bk0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932073Ab3IMNJ4 (ORCPT ); Fri, 13 Sep 2013 09:09:56 -0400 MIME-Version: 1.0 In-Reply-To: <5232DB49.4050701@arm.com> References: <1378968687-8200-1-git-send-email-cinifr@gmail.com> <1378968687-8200-4-git-send-email-cinifr@gmail.com> <20130912112452.GA22013@e106331-lin.cambridge.arm.com> <5231EE43.5090900@arm.com> <5232DB49.4050701@arm.com> Date: Fri, 13 Sep 2013 21:09:55 +0800 Message-ID: Subject: Re: [PATCH 3/4] Add physical count arch timer support for clocksource in ARMv7. From: cinifr To: Marc Zyngier Cc: Mark Rutland , "coosty@163.com" , "maxime.ripard@free-electrons.com" , "daniel.lezcano@linaro.org" , "linux@arm.linux.org.uk" , "tglx@linutronix.de" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "pawel.moll@arm.co" , "rob.herring@calxeda.com" , "linux-sunxi@googlegroups.com" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1723 Lines: 36 > I urge you to read the ARM ARM, and specifically the section dedicated > to trapping access to CP15 operations. If you do, you'll quickly notice > that you *cannot* trap accesses to the timer subsystem. > I read it again. The ARMv7 manual said "Is accessible from Non-secure PL1 modes only when CNTHCTL.PL1PCTEN is set to 1. When CNTHCTL.PL1PCTEN is set to 0, any attempt to access CNTPCT from a Non-secure PL1 mode ***generates a Hyp Trap exception***, see Hyp Trap exception on page B1-1206" in B8.1.2. but I dont find a special hyp trap control for accessing CNTPCT in manual. As you said HSTR cannot trap accessing of CP15 c14. What happer when OS access CNTPCT from PL1 NS=1 mode with CNTHCTL.PL1PCTEN=0 ??? AmI wrong for understanding the manual? Thanks. BTW: And I fond xen have support to trap accessing CNTPCT by this patch on http://lists.xen.org/archives/html/xen-devel/2012-08/msg00452.html. > All you can do is disable access to the physical timer/counter, > resulting in an UNDEF in the *guest*. > > Additionally, please realise the overhead of trapping is enormous, and > that we do try very hard to minimise it. Why do you think we went out of > our way to ensure that host and guest would use different timers, always? > > CNTVOFF can only be setup from either HYP or Secure Monitor mode with > SCR.NS == 1, so if you run your kernel in secure mode, it is always best > to do it in the bootloader. I agree it, Bootloader do it better. Fan -- 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/