From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752645AbeEKJZX (ORCPT ); Fri, 11 May 2018 05:25:23 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:38586 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752272AbeEKJZW (ORCPT ); Fri, 11 May 2018 05:25:22 -0400 Subject: Re: [PATCH 0/2] Allwinner A64 timer workaround To: Samuel Holland , Maxime Ripard , Chen-Yu Tsai , Catalin Marinas , Will Deacon , Daniel Lezcano , Thomas Gleixner , Marc Zyngier Cc: linux-sunxi@googlegroups.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org References: <20180511022751.9096-1-samuel@sholland.org> From: Andre Przywara Message-ID: <9d12075e-745d-b7d7-9847-f1493fc8647e@arm.com> Date: Fri, 11 May 2018 10:24:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180511022751.9096-1-samuel@sholland.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 11/05/18 03:27, Samuel Holland wrote: > Hello, > > Several people (including me) have experienced extremely large system > clock jumps on their A64-based devices, apparently due to the > architectural timer going backward, which is interpreted by Linux as > the timer wrapping around after 2^56 cycles. So I experienced this before, though I didn't see actual clock jumps, only that subsequent reads of CNTVCT_EL0, both directly via mrs and indirectly via CLOCK_MONOTONIC, from userland (triggered by a directed test) *sometimes* went backwards, with a number of '1's in the lower bits. But that didn't happen on every boot, and I was suspecting that some timer setup was missing on the hardware/firmware side. And later on I failed to reproduce it anymore. So do you see it on every boot, with recent U-Boot/ATF? Cheers, Andre. > Investigation led to discovery of some obvious problems with this SoC's > architectural timer, and this patch series introduces what I believe is > the simplest workaround. More details are in the commit message for > patch 1. Patch 2 simply enables the workaround in the device tree. > > Thanks, > Samuel > > Samuel Holland (2): > arm64: arch_timer: Workaround for Allwinner A64 timer instability > arm64: dts: allwinner: a64: Enable A64 timer workaround > > arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 1 + > drivers/clocksource/Kconfig | 11 ++++++++ > drivers/clocksource/arm_arch_timer.c | 39 +++++++++++++++++++++++++++ > 3 files changed, 51 insertions(+) > > -- > 2.16.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >