From owner-svn-src-head@FreeBSD.ORG Mon Feb 9 19:10:42 2009 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id A7264106566C for ; Mon, 9 Feb 2009 19:10:42 +0000 (UTC) (envelope-from sam@freebsd.org) Received: from ebb.errno.com (ebb.errno.com [69.12.149.25]) by mx1.freebsd.org (Postfix) with ESMTP id 5832D8FC26 for ; Mon, 9 Feb 2009 19:10:42 +0000 (UTC) (envelope-from sam@freebsd.org) Received: from trouble.errno.com (trouble.errno.com [10.0.0.248]) (authenticated bits=0) by ebb.errno.com (8.13.6/8.12.6) with ESMTP id n19JAeZE021049 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 9 Feb 2009 11:10:40 -0800 (PST) (envelope-from sam@freebsd.org) Message-ID: <49907FB0.9050901@freebsd.org> Date: Mon, 09 Feb 2009 11:10:40 -0800 From: Sam Leffler Organization: FreeBSD Project User-Agent: Thunderbird 2.0.0.18 (X11/20081209) MIME-Version: 1.0 To: "M. Warner Losh" References: <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com> <20090209.113053.65361811.imp@bsdimp.com> <49907B32.8080307@samsco.org> <20090209.115932.1098202471.imp@bsdimp.com> In-Reply-To: <20090209.115932.1098202471.imp@bsdimp.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-DCC-URT-Metrics: ebb.errno.com; whitelist Cc: scottl@samsco.org, src-committers@freebsd.org, jhb@freebsd.org, svn-src-all@freebsd.org, xcllnt@mac.com, svn-src-head@freebsd.org Subject: Re: svn commit: r188350 - in head/sys: amd64/amd64 arm/arm dev/usb2/core i386/i386 ia64/ia64 sys X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Feb 2009 19:10:43 -0000 M. Warner Losh wrote: > In message: <49907B32.8080307@samsco.org> > Scott Long writes: > : M. Warner Losh wrote: > : > In message: <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com> > : > Marcel Moolenaar writes: > : > : > : > : On Feb 9, 2009, at 6:23 AM, John Baldwin wrote: > : > : > : > : > On Monday 09 February 2009 12:37:53 am Marcel Moolenaar wrote: > : > : >> > : > : >> On Feb 8, 2009, at 5:00 PM, Scott Long wrote: > : > : >> > : > : >>> Busdma allows you to request bouncing for realignment. > : > : >> > : > : >> How exactly? > : > : > > : > : > The 'align' parameter to bus_dma_tag_create(). If your hardware > : > : > needs buffers > : > : > to be aligned on a 4-byte boundary and you bus_dmamap_load() a buffer > : > : > where 'addr % 4 != 0', then the buffer is bounced. Since by default > : > : > the new > : > : > buffer starts on a page boundary, it satifies the 'addr % 4'. > : > : > : > : But according to the man page, bounce buffering may not > : > : be implemented or not be applicable to a platform. It > : > : seems to me that you cannot depend on this side-effect > : > : in a generic driver. Are you guys talking only in terms > : > : of i386 or is this generally applicable? > : > > : > There's no bounce buffering on MIPS right now, for example... There > : > likely should be, but it isn't there now. > : > > : > Warner > : > : So yes, it's only available really on amd64 and i386 at the moment. No > : reason why it can't be available elsewhere, and I'm working on factoring > : all of the bounce logic out into an MD file so it can be made available. > : For architectures that use an IOMMU, there's probably no reason why > : re-alignment can't use the IOMMU instead of bouncing. > > arm also does bounce buffering, but not for memory address space reasons. > Not sure what you mean my "address space reasons" but it bounces for PCI dma above 64M on ixp4xx. Sam