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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 0579DC433E0 for ; Sat, 30 Jan 2021 01:40:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A67D264D7F for ; Sat, 30 Jan 2021 01:40:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232473AbhA3Bi1 (ORCPT ); Fri, 29 Jan 2021 20:38:27 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:12355 "EHLO szxga07-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231426AbhA3Bfu (ORCPT ); Fri, 29 Jan 2021 20:35:50 -0500 Received: from DGGEMS413-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4DSGvK0yY4z7d2C; Sat, 30 Jan 2021 09:33:49 +0800 (CST) Received: from [127.0.0.1] (10.174.176.220) by DGGEMS413-HUB.china.huawei.com (10.3.19.213) with Microsoft SMTP Server id 14.3.498.0; Sat, 30 Jan 2021 09:34:56 +0800 Subject: Re: [PATCH v3 2/3] perf/smmuv3: Add a MODULE_SOFTDEP() to indicate dependency on SMMU To: Robin Murphy , John Garry , Will Deacon , Mark Rutland , "Joerg Roedel" , linux-arm-kernel , iommu , linux-kernel CC: Jean-Philippe Brucker References: <20210127113258.1421-1-thunder.leizhen@huawei.com> <20210127113258.1421-3-thunder.leizhen@huawei.com> <67e0859b-2633-3516-527f-57557e210fa1@arm.com> <4b116f38-84da-9ef9-350c-8900944b0433@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: Date: Sat, 30 Jan 2021 09:34:55 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.220] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/1/30 1:03, Robin Murphy wrote: > On 2021-01-29 15:34, John Garry wrote: >> On 29/01/2021 15:12, Robin Murphy wrote: >>> On 2021-01-27 11:32, Zhen Lei wrote: >>>> The MODULE_SOFTDEP() gives user space a hint of the loading sequence. And >>>> when command "modprobe arm_smmuv3_pmu" is executed, the arm_smmu_v3.ko is >>>> automatically loaded in advance. >>> >>> Why do we need this? If probe order doesn't matter when both drivers are built-in, why should module load order? >>> >>> TBH I'm not sure why we even have a Kconfig dependency on ARM_SMMU_V3, given that the drivers operate completely independently :/ >> >> Can that Kconfig dependency just be removed? I think that it was added under the idea that there is no point in having the SMMUv3 PMU driver without the SMMUv3 driver. > > A PMCG *might* be usable for simply counting transactions to measure device activity regardless of its associated SMMU being enabled. If that's the case, the SOFTDEP really shouldn't be added. I wasn't trying to make sure they were loaded in order, just to make sure that the SMMU was not forgotten to load. > Either way, it's not really Kconfig's job to decide what makes sense (beyond the top-level "can this driver *ever* be used on this platform" visibility choices). Imagine if we gave every PCI/USB/etc. device driver an explicit ?dependency on at least one host controller driver being enabled... > > Robin. > > . >