From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 940AAC18DF5 for ; Tue, 20 Nov 2018 14:55:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4F5242147A for ; Tue, 20 Nov 2018 14:55:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F5242147A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730114AbeKUBZA (ORCPT ); Tue, 20 Nov 2018 20:25:00 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:50346 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727466AbeKUBY7 (ORCPT ); Tue, 20 Nov 2018 20:24:59 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4F790EBD; Tue, 20 Nov 2018 06:55:27 -0800 (PST) Received: from [10.1.196.62] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D76C13F5A0; Tue, 20 Nov 2018 06:55:24 -0800 (PST) Subject: Re: [PATCH v1 1/1] arm64: Early boot time stamps To: Pavel Tatashin Cc: catalin.marinas@arm.com, will.deacon@arm.com, Andrew Morton , rppt@linux.vnet.ibm.com, Michal Hocko , Ard Biesheuvel , andrew.murray@arm.com, james.morse@arm.com, sboyd@kernel.org, linux-arm-kernel@lists.infradead.org, LKML References: <20181119214443.25175-1-pasha.tatashin@soleen.com> <20181119214443.25175-2-pasha.tatashin@soleen.com> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/11/2018 14:40, Pavel Tatashin wrote: >>> +static __init void sched_clock_early_init(void) >>> +{ >>> + u64 freq = arch_timer_get_cntfrq(); >>> + u64 (*read_time)(void) = arch_counter_get_cntvct; >> >> We already have arch_timer_read_counter which is exposed from >> arm_arch_timer.h. > > OK > >> >>> + >>> + /* Early clock is available only on platforms with known freqs */ >> >> This comment is misleading. It should read something like: >> >> /* >> * The arm64 boot protocol mandates that CNTFRQ_EL0 reflects >> * the timer frequency. To avoid breakage on misconfigured >> * systems, do not register the early sched_clock if the >> * programmed value if zero. Other random values will just >> * result in random output. >> */ >> > > OK > >>> + if (!freq) >>> + return; >>> + >>> + sched_clock_register(read_time, BITS_PER_LONG, freq); >> >> This doesn't seem right. The counter has an architected minimum of 56 >> bits, and you can't assume that it is going to be more than that. > > Yeah, I saw 56 is used in arm_arch_timer.c, but I could not find where > this minimum is defined in aarch64 specs. I will change it to 56. See D10.1.2 (The system counter) in the ARM ARM[1], which says: The Generic Timer provides a system counter with the following specification: Width At least 56 bits wide. The value returned by any 64-bit read of the counter is zero-extended to 64 bits. This is not AArch64-specific though, and 32bit systems implementing the generic timers have the exact same requirements. > I will send v2 soon. Please wait a bit and give others a chance to review this too. Thanks, M. [1] https://static.docs.arm.com/ddi0487/da/DDI0487D_a_armv8_arm.pdf -- Jazz is not dead. It just smells funny...