From owner-svn-src-all@FreeBSD.ORG Mon Feb 9 17:51:53 2009 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7F33D106566B; Mon, 9 Feb 2009 17:51:53 +0000 (UTC) (envelope-from xcllnt@mac.com) Received: from asmtpout020.mac.com (asmtpout020.mac.com [17.148.16.95]) by mx1.freebsd.org (Postfix) with ESMTP id 64EEE8FC0A; Mon, 9 Feb 2009 17:51:53 +0000 (UTC) (envelope-from xcllnt@mac.com) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; charset=US-ASCII; format=flowed; delsp=yes Received: from rajreddy-lnx.jnpr.net (natint3.juniper.net [66.129.224.36]) by asmtp020.mac.com (Sun Java(tm) System Messaging Server 6.3-7.03 (built Aug 7 2008; 32bit)) with ESMTPSA id <0KET007VS89UH380@asmtp020.mac.com>; Mon, 09 Feb 2009 09:51:34 -0800 (PST) Message-id: <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com> From: Marcel Moolenaar To: John Baldwin In-reply-to: <200902090923.45887.jhb@freebsd.org> Date: Mon, 09 Feb 2009 09:51:28 -0800 References: <200902082254.n18MsxVt037307@svn.freebsd.org> <498F8015.8000704@samsco.org> <94616FBD-4638-4C51-990C-06A943B1BA2A@mac.com> <200902090923.45887.jhb@freebsd.org> X-Mailer: Apple Mail (2.930.3) Cc: svn-src-head@freebsd.org, Scott Long , src-committers@freebsd.org, svn-src-all@freebsd.org, "M. Warner Losh" Subject: Re: svn commit: r188350 - in head/sys: amd64/amd64 arm/arm dev/usb2/core i386/i386 ia64/ia64 sys X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Feb 2009 17:51:54 -0000 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? -- Marcel Moolenaar xcllnt@mac.com