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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 D9526C43141 for ; Thu, 14 Nov 2019 08:14:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2FB620718 for ; Thu, 14 Nov 2019 08:14:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726516AbfKNIO3 (ORCPT ); Thu, 14 Nov 2019 03:14:29 -0500 Received: from verein.lst.de ([213.95.11.211]:38174 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725965AbfKNIO3 (ORCPT ); Thu, 14 Nov 2019 03:14:29 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 3B6EC68BFE; Thu, 14 Nov 2019 09:14:23 +0100 (CET) Date: Thu, 14 Nov 2019 09:14:23 +0100 From: Christoph Hellwig To: Lu Baolu Cc: Christoph Hellwig , David Woodhouse , Joerg Roedel , Bjorn Helgaas , ashok.raj@intel.com, jacob.jun.pan@intel.com, alan.cox@intel.com, kevin.tian@intel.com, mika.westerberg@linux.intel.com, Ingo Molnar , Greg Kroah-Hartman , pengfei.xu@intel.com, Konrad Rzeszutek Wilk , Marek Szyprowski , Robin Murphy , Jonathan Corbet , Boris Ostrovsky , Juergen Gross , Stefano Stabellini , Steven Rostedt , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Jacob Pan Subject: Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma_ops Message-ID: <20191114081423.GA27407@lst.de> References: <20190725031717.32317-3-baolu.lu@linux.intel.com> <20190725054413.GC24527@lst.de> <20190725114348.GA30957@lst.de> <20191112071640.GA3343@lst.de> <0885617e-8390-6d18-987f-40d49f9f563e@linux.intel.com> <20191113070312.GA2735@lst.de> <20191113095353.GA5937@lst.de> <0ddc8aff-783a-97b9-f5cc-9e27990de278@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0ddc8aff-783a-97b9-f5cc-9e27990de278@linux.intel.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 14, 2019 at 01:14:11PM +0800, Lu Baolu wrote: > Could you please educate me what dma_supported() is exactly for? Will > it always get called during boot? When will it be called? ->dma_supported is set when setting either the dma_mask or dma_coherent_mask. These days it serves too primary purposes: reject too small masks that can't be addressed, and provide any hooks needed in the driver based on the mask. > In above implementation, why do we need to check dma_direct_supported() > at the beginning? And why Because the existing driver called dma_direct_supported, which I added based on x86 arch overrides doings the same a while ago. I suspect it is related to addressing for tiny dma masks, but I'm not entirely sure. The longer term intel-iommu maintainers or x86 maintainers might be able to shed more light how this was supposed to work and/or how systems with the Intel IOMMU deal with e.g. ISA devices with 24-bit addressing. > > if (!info || info == DUMMY_DEVICE_DOMAIN_INFO || > info == DEFER_DEVICE_DOMAIN_INFO) { > dev->dma_ops_bypass = true; This was supposed to transform the checks from iommu_dummy and identity_mapping. But I think it actually isn't entirely correct and already went bad in the patch to remove identity_mapping. Pleae check the branch I just re-pushed, which should be correct now.