From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from pandora.arm.linux.org.uk (pandora.arm.linux.org.uk [IPv6:2001:4d48:ad52:3201:214:fdff:fe10:1be6]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 7B95D2C0097 for ; Sun, 23 Mar 2014 09:23:58 +1100 (EST) Date: Sat, 22 Mar 2014 22:23:06 +0000 From: Russell King - ARM Linux To: James Bottomley Subject: Re: [RESEND][PATCH 1/2] lib/scatterlist: Make ARCH_HAS_SG_CHAIN an actual Kconfig Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1395523881.2143.58.camel@dabdike.int.hansenpartnership.com> Sender: Russell King - ARM Linux 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, 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. 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. -- FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly improving, and getting towards what was expected from it.