From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 2/2] arch: switch the default on ARCH_HAS_SG_CHAIN Date: Mon, 19 Nov 2018 14:58:52 +0100 Message-ID: <20181119135852.GA16428@lst.de> References: <20181109090008.24150-3-hch@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Palmer Dabbelt Cc: Christoph Hellwig , iommu@lists.linux-foundation.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-arch.vger.kernel.org On Fri, Nov 16, 2018 at 08:52:14AM -0800, Palmer Dabbelt wrote: > As far as I can tell, it looks like m68k, mips, and powerpc mention an > IOMMU in their ports, don't set ARCH_HAS_SG_CHAIN, and with this patch set > won't set ARCH_NO_SG_CHAIN. m68k has no iommu, and not operations that operate on a scatterlist. mips has a trivial iommu driver (jazzdma), but I wrote the current instance of it, nad it is fine. powerpc has various iommu, but actually enables ARCH_HAS_SG_CHAIN unconditionally. > The issue is that I'm not sure how to > determine what constitutes a horrible legacy IOMMU, at least with respect > to not being able to use scatterlist chaining. It basically means someone is iterating using manual pointer arithmetics over a multi-element scatterlist instead of using the sg_next and for_each_sg helpers. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from verein.lst.de ([213.95.11.211]:38215 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728258AbeKTAWg (ORCPT ); Mon, 19 Nov 2018 19:22:36 -0500 Date: Mon, 19 Nov 2018 14:58:52 +0100 From: Christoph Hellwig Subject: Re: [PATCH 2/2] arch: switch the default on ARCH_HAS_SG_CHAIN Message-ID: <20181119135852.GA16428@lst.de> References: <20181109090008.24150-3-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Palmer Dabbelt Cc: Christoph Hellwig , iommu@lists.linux-foundation.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <20181119135852.VPjdYcD2qbKzDFOWORSLzHEXZwWMsWpzi475ppqfhm0@z> On Fri, Nov 16, 2018 at 08:52:14AM -0800, Palmer Dabbelt wrote: > As far as I can tell, it looks like m68k, mips, and powerpc mention an > IOMMU in their ports, don't set ARCH_HAS_SG_CHAIN, and with this patch set > won't set ARCH_NO_SG_CHAIN. m68k has no iommu, and not operations that operate on a scatterlist. mips has a trivial iommu driver (jazzdma), but I wrote the current instance of it, nad it is fine. powerpc has various iommu, but actually enables ARCH_HAS_SG_CHAIN unconditionally. > The issue is that I'm not sure how to > determine what constitutes a horrible legacy IOMMU, at least with respect > to not being able to use scatterlist chaining. It basically means someone is iterating using manual pointer arithmetics over a multi-element scatterlist instead of using the sg_next and for_each_sg helpers.