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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 0C53CC3F2D2 for ; Fri, 28 Feb 2020 10:32:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC5F7246A8 for ; Fri, 28 Feb 2020 10:32:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726413AbgB1Kcj (ORCPT ); Fri, 28 Feb 2020 05:32:39 -0500 Received: from foss.arm.com ([217.140.110.172]:36262 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726063AbgB1Kcj (ORCPT ); Fri, 28 Feb 2020 05:32:39 -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 6E58D4B2; Fri, 28 Feb 2020 02:32:38 -0800 (PST) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 23C973F73B; Fri, 28 Feb 2020 02:32:36 -0800 (PST) Date: Fri, 28 Feb 2020 10:32:34 +0000 From: Catalin Marinas To: Ionela Voinescu Cc: will@kernel.org, mark.rutland@arm.com, maz@kernel.org, suzuki.poulose@arm.com, sudeep.holla@arm.com, lukasz.luba@arm.com, valentin.schneider@arm.com, dietmar.eggemann@arm.com, rjw@rjwysocki.net, pkondeti@codeaurora.org, 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 Subject: Re: [PATCH v5 1/7] arm64: add support for the AMU extension v1 Message-ID: <20200228103234.GA3904776@arrakis.emea.arm.com> References: <20200226132947.29738-1-ionela.voinescu@arm.com> <20200226132947.29738-2-ionela.voinescu@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200226132947.29738-2-ionela.voinescu@arm.com> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Ionela, On Wed, Feb 26, 2020 at 01:29:41PM +0000, Ionela Voinescu wrote: > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index dbc22d684627..49f0c436928f 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -318,6 +318,15 @@ > Format: , > See also Documentation/input/joydev/joystick.rst > > + amu= [ARM64] > + Enables or disables detection, enablement and access to > + counter registers of the Activity Monitors Unit (AMU). > + Format: amu=[0/1/on/off/y/n] > + amu=[0/off/n] ensures access to AMU's counter registers > + is not attempted. > + amu=[1/on/y] (default) enables detection and access to > + AMU's counter registers. Is the only reason for this parameter to be able to disable the feature if the firmware doesn't support it? According to the Kconfig entry, you may see weird behaviour, firmware lock-up. Is the user supposed to try again with amu=0? I'm not particularly fond of adding kernel parameters to work around broken firmware. We have other architecture features (e.g. PtrAuth) that need enabling at EL3 but we don't have such parameters. If it's likely that we hit this issue in practice, I'd rather have the firmware describing the presence of AMU via some DT entry. But I'd rather not bother at all, just get the vendors to update their firmware. If we drop this parameter, patch 1 would need to change. Otherwise the patches look fine. Thanks. -- Catalin