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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 377D5C3F68F for ; Wed, 12 Feb 2020 10:02:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 150EC20848 for ; Wed, 12 Feb 2020 10:02:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728987AbgBLKCB (ORCPT ); Wed, 12 Feb 2020 05:02:01 -0500 Received: from foss.arm.com ([217.140.110.172]:58362 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728843AbgBLKCB (ORCPT ); Wed, 12 Feb 2020 05:02:01 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 516BF30E; Wed, 12 Feb 2020 02:02:00 -0800 (PST) Received: from [10.37.12.187] (unknown [10.37.12.187]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BCACC3F68F; Wed, 12 Feb 2020 02:01:56 -0800 (PST) Subject: Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate To: Ionela Voinescu , catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, maz@kernel.org, suzuki.poulose@arm.com, sudeep.holla@arm.com, valentin.schneider@arm.com, rjw@rjwysocki.net Cc: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org, viresh.kumar@linaro.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org References: <20200211184542.29585-1-ionela.voinescu@arm.com> <20200211184542.29585-8-ionela.voinescu@arm.com> From: Lukasz Luba Message-ID: <89339501-5ee4-e871-3076-c8b02c6fbf6e@arm.com> Date: Wed, 12 Feb 2020 10:01:54 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200211184542.29585-8-ionela.voinescu@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Ionela, Valentin On 2/11/20 6:45 PM, Ionela Voinescu wrote: > From: Valentin Schneider > > Using an arch timer with a frequency of less than 1MHz can result in an > incorrect functionality of the system which assumes a reasonable rate. > > One example is the use of activity monitors for frequency invariance > which uses the rate of the arch timer as the known rate of the constant > cycle counter in computing its ratio compared to the maximum frequency > of a CPU. For arch timer frequencies less than 1MHz this ratio could > end up being 0 which is an invalid value for its use. > > Therefore, warn if the arch timer rate is below 1MHz which contravenes > the recommended architecture interval of 1 to 50MHz. > > Signed-off-by: Ionela Voinescu > Cc: Mark Rutland > Cc: Marc Zyngier > --- > drivers/clocksource/arm_arch_timer.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > index 9a5464c625b4..4faa930eabf8 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -885,6 +885,17 @@ static int arch_timer_starting_cpu(unsigned int cpu) > return 0; > } > > +static int validate_timer_rate(void) > +{ > + if (!arch_timer_rate) > + return -EINVAL; > + > + /* Arch timer frequency < 1MHz can cause trouble */ > + WARN_ON(arch_timer_rate < 1000000); I don't see a big value of having a patch just to add one extra warning, in a situation which we handle in our code with in 6/7 with: + if (!ratio) { + pr_err("System timer frequency too low.\n"); + return -EINVAL; + } Furthermore, the value '100000' here is because of our code and calculation in there, so it does not belong to arch timer. Someone might ask why it's not 200000 or a define in our header... Or questions asking why do you warn when that arch timer and cpu is not AMU capable... > + > + return 0; > +} > + > /* > * For historical reasons, when probing with DT we use whichever (non-zero) > * rate was probed first, and don't verify that others match. If the first node > @@ -900,7 +911,7 @@ static void arch_timer_of_configure_rate(u32 rate, struct device_node *np) > arch_timer_rate = rate; > > /* Check the timer frequency. */ > - if (arch_timer_rate == 0) > + if (validate_timer_rate()) > pr_warn("frequency not available\n"); > } > > @@ -1594,9 +1605,10 @@ static int __init arch_timer_acpi_init(struct acpi_table_header *table) > * CNTFRQ value. This *must* be correct. > */ > arch_timer_rate = arch_timer_get_cntfrq(); > - if (!arch_timer_rate) { > + ret = validate_timer_rate(); > + if (ret) { > pr_err(FW_BUG "frequency not available.\n"); > - return -EINVAL; > + return ret; > } > > arch_timer_uses_ppi = arch_timer_select_ppi(); > Lastly, this is arch timer. To increase chances of getting merge soon, I would recommend to drop the patch from this series. Regards, Lukasz