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 D8361C3B186 for ; Wed, 12 Feb 2020 10:56:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B520D20675 for ; Wed, 12 Feb 2020 10:56:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727163AbgBLK4E (ORCPT ); Wed, 12 Feb 2020 05:56:04 -0500 Received: from foss.arm.com ([217.140.110.172]:59170 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725821AbgBLK4E (ORCPT ); Wed, 12 Feb 2020 05:56:04 -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 6060030E; Wed, 12 Feb 2020 02:56:03 -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 2FCBE3F68F; Wed, 12 Feb 2020 02:56:00 -0800 (PST) Subject: Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate To: Marc Zyngier Cc: Ionela Voinescu , catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, suzuki.poulose@arm.com, sudeep.holla@arm.com, valentin.schneider@arm.com, rjw@rjwysocki.net, 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> <89339501-5ee4-e871-3076-c8b02c6fbf6e@arm.com> From: Lukasz Luba Message-ID: <289c6110-b7ea-1d61-d795-551723263803@arm.com> Date: Wed, 12 Feb 2020 10:55:58 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 2/12/20 10:12 AM, Marc Zyngier wrote: > On 2020-02-12 10:01, Lukasz Luba wrote: >> 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... > > Because, as the commit message outlines it, such a frequency is terribly > out of spec? I don't see in the RM that < 1MHz is terribly out of spec. 'Frequency Increments at a fixed frequency, typically in the range 1-50MHz. Can support one or more alternative operating modes in which it increments by larger amounts at a lower frequency, typically for power-saving.' There is even an example how to operate at 20kHz and increment by 500. I don't know the code if it's supported, thought. > >> >>> + >>> +    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. > > And? It seems to address a potential issue where the time frequency > is out of spec, and makes sure we don't end up with additional problems > in the AMU code. This patch just prints warning, does not change anything in booting or in any code related to AMU. > > On its own, it is perfectly sensible and could be merged as part of this > series with my > > Acked-by: Marc Zyngier > >         M. Regards, Lukasz