From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 56C2F3A7826; Tue, 24 Feb 2026 15:57:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.176.79.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771948669; cv=none; b=YBBJX60BiXCAfnPUebU3VDVKzeys2apVG/6zCWsHepaOoK9Tsu8DlplMlGsQyPtYoRnEJVygIKs1eSKoaH8q+N9Fk3JunlwBdM8YzUyuPJQ1EGkEwXLD+jZCgfl25kkxdaA608dFyFm6vBSkow1rXExyPsTSOno/rp/DwFUxA6Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771948669; c=relaxed/simple; bh=3HmCSU8v0qUIZEPgi6VtfWbbw6DAODzcruLTpi09h4E=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=AdAW8Ybl1j+XjkWlKMKdwaVmF/3P+IGhkj9IH4Sat3ocYs7sT/wOQm44PLLMpAJNlsyHqkFzUL0V52zBxumHrqbPprsrmZZcL0kZJxtKOhoTPH7GVvKAgE24oWX6h44EwOZrWE+k6RhgBHSw/GhrtZk83DdEFVHg1IaUE1Dwny4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=185.176.79.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com 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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: lhrpeml100011.china.huawei.com (7.191.174.247) To dubpeml500005.china.huawei.com (7.214.145.207) 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 >