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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D110DF3C9A8 for ; Tue, 24 Feb 2026 15:57:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Subject:CC:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=tv9tDjFPNsZB0EIWyR3fsFVW00y9HH6AxTenWSD/bjI=; b=elc1oKZCUdxDyzU6r787GU6NSh SePycd9IB1HkiEUOQ6XHFWZSPrwZbUWQNMX50sBpk0Fync6IQY9ezLJoQAhy4mjD31qG9bTFkCi0D xMQmSrj0e1eABPoOQNe8mUYeBewcQ41HJYEzrdGa3goiNBHfmWQXtATmrsxmgUg96daoGplBYApx4 pTYt7LHnb9DVo8WDcKIejx0g9taTOlTOrUGDgbcMZMXtn+V2Cy3kg85EMnI/lR0S+Ay6rYcMQ9lxu SgEud5IQt3SnJmatTFQv+NCfOmGVQ1iwIk616y1yinytghL4BK7n0ztF6C9dKQNI0LtjFPeNIUcg/ EyDAd6Cg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vuunF-00000002MSY-0Hgw; Tue, 24 Feb 2026 15:57:49 +0000 Received: from frasgout.his.huawei.com ([185.176.79.56]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vuunC-00000002MRy-1TVS for linux-arm-kernel@lists.infradead.org; Tue, 24 Feb 2026 15:57:47 +0000 Received: from mail.maildlp.com (unknown [172.18.224.150]) by frasgout.his.huawei.com (SkyGuard) with ESMTPS id 4fL2RQ5VB5zJ46Zj; Tue, 24 Feb 2026 23:57:22 +0800 (CST) Received: from dubpeml500005.china.huawei.com (unknown [7.214.145.207]) by mail.maildlp.com (Postfix) with ESMTPS id 8DCEA40539; Tue, 24 Feb 2026 23:57:44 +0800 (CST) Received: from localhost (10.203.177.15) by dubpeml500005.china.huawei.com (7.214.145.207) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 24 Feb 2026 15:57:43 +0000 Date: Tue, 24 Feb 2026 15:57:42 +0000 From: Jonathan Cameron To: Jason Gunthorpe CC: Nicolin Chen , , , , , , , , , , , , , Subject: Re: [PATCH v2 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Message-ID: <20260224155742.00000282@huawei.com> In-Reply-To: References: <20260224120615.00003ad9@huawei.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.203.177.15] X-ClientProxiedBy: lhrpeml100011.china.huawei.com (7.191.174.247) To dubpeml500005.china.huawei.com (7.214.145.207) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260224_075746_543516_4BE53BDC X-CRM114-Status: GOOD ( 15.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 24 Feb 2026 10:51:02 -0400 Jason Gunthorpe wrote: > On Tue, Feb 24, 2026 at 12:06:15PM +0000, Jonathan Cameron wrote: > > > In my head at least, it would be nice if a driver had to explicitly opt in > > to this behavior. The presence of CXL.cache support for instance doesn't > > actually mean the driver is going to enable it. However it is probably > > harmless so lets go with this as path of least resistance. > > That same remark applies to ATS in general, we have no idea if the > device is going to use it when turned on or not.. Yup. Understood. That's the bit that smells bad to me. > > Generally Linux has taken the approach of almost always enabling ATS > if the device offers the PCIe capability. > > The purpose of this series is to close of the few "almost" cases so it > is always on. Absolutely understood. I just took the opportunity to moan! J > > Jason >