From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bedivere.hansenpartnership.com (bedivere.hansenpartnership.com [66.63.167.143]) by ozlabs.org (Postfix) with ESMTP id 0C3E12C0079 for ; Sun, 23 Mar 2014 09:37:45 +1100 (EST) Message-ID: <1395527860.2143.61.camel@dabdike.int.hansenpartnership.com> Subject: Re: [RESEND][PATCH 1/2] lib/scatterlist: Make ARCH_HAS_SG_CHAIN an actual Kconfig From: James Bottomley To: Russell King - ARM Linux Date: Sat, 22 Mar 2014 15:37:40 -0700 In-Reply-To: <20140322222306.GM7528@n2100.arm.linux.org.uk> References: <1395512032-20575-1-git-send-email-lauraa@codeaurora.org> <1395512032-20575-2-git-send-email-lauraa@codeaurora.org> <1395523881.2143.58.camel@dabdike.int.hansenpartnership.com> <20140322222306.GM7528@n2100.arm.linux.org.uk> Content-Type: text/plain; charset="ISO-8859-15" Mime-Version: 1.0 Cc: Fenghua Yu , linux-ia64@vger.kernel.org, Tony Luck , Laura Abbott , linux-scsi@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, Heiko Carstens , linux-kernel@vger.kernel.org, "David S. Miller" , Martin Schwidefsky , Ingo Molnar , Paul Mackerras , "H. Peter Anvin" , sparclinux@vger.kernel.org, linux390@de.ibm.com, Andrew Morton , linuxppc-dev@lists.ozlabs.org, Thomas Gleixner , linux-arm-kernel@lists.infradead.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, 2014-03-22 at 22:23 +0000, Russell King - ARM Linux wrote: > On Sat, Mar 22, 2014 at 02:31:21PM -0700, James Bottomley wrote: > > Perhaps now might be the time to ask which are the remaining > > architectures that cannot do SG chaining and then we can fix them and > > pull the whole thing out. > > Not quite. You're making the assumption that we can be sure that all > the scatterlist users on an architecture have been converted - that's > simply not true on ARM. No I'm not, I said "now might be the time to ask which are the remaining architectures that cannot do SG chaining" I think it's time to list them so we know what work remains. I know we've got a bunch in parisc (all of our iommu code in driver/parisc - about 5 different ones - are unconverted). However, the conversion is pretty simple; it's mostly replacing sglist++ with sglist=sg_next(sglist) > We have some which have, and some which still > have not been audited. > > The cases that get us here would be old platform DMA code which walks > scatterlists handed to it from drivers - stuff like > arch/arm/mach-rpc/dma.c (which probably can cope), and drivers/scsi/arm/* > (which definitely can't because of their SCSI pointers save/restore > handling message.) I know that's one case where SG_CHAIN definitely > isn't supported on ARM. > > So, we had decided not to enable it, but this means that new stuff > isn't benefitting from this. I've recently asked arm-soc to enable > it for the modern multi-platform builds, because modern stuff really > be written with correct SG chaining in mind. OK, so lets see what the actual effort is. James