From owner-svn-src-head@FreeBSD.ORG Mon Feb 9 01:00:12 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 3FD3B106568F; Mon, 9 Feb 2009 01:00:12 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.freebsd.org (Postfix) with ESMTP id B42598FC1D; Mon, 9 Feb 2009 01:00:11 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from phobos.local ([192.168.254.200]) (authenticated bits=0) by pooker.samsco.org (8.14.2/8.14.2) with ESMTP id n19105Tc044067; Sun, 8 Feb 2009 18:00:05 -0700 (MST) (envelope-from scottl@samsco.org) Message-ID: <498F8015.8000704@samsco.org> Date: Sun, 08 Feb 2009 18:00:05 -0700 From: Scott Long User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8.1.13) Gecko/20080313 SeaMonkey/1.1.9 MIME-Version: 1.0 To: Marcel Moolenaar References: <200902082254.n18MsxVt037307@svn.freebsd.org> <9E40268E-A2E2-4CAA-AAFE-EB2491175CEE@mac.com> <20090208.170515.1031215309.imp@bsdimp.com> <34EFBA0C-FB99-42DB-BF5C-A889348AD393@mac.com> In-Reply-To: <34EFBA0C-FB99-42DB-BF5C-A889348AD393@mac.com> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.4 required=3.8 tests=ALL_TRUSTED,BAYES_00 autolearn=ham version=3.1.8 X-Spam-Checker-Version: SpamAssassin 3.1.8 (2007-02-13) on pooker.samsco.org Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@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-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 01:00:13 -0000 Marcel Moolenaar wrote: > > On Feb 8, 2009, at 4:05 PM, M. Warner Losh wrote: > >> In message: <9E40268E-A2E2-4CAA-AAFE-EB2491175CEE@mac.com> >> Marcel Moolenaar writes: >> : >> : On Feb 8, 2009, at 2:54 PM, Warner Losh wrote: >> : >> : > Author: imp >> : > Date: Sun Feb 8 22:54:58 2009 >> : > New Revision: 188350 >> : > URL: http://svn.freebsd.org/changeset/base/188350 >> : > >> : > Log: >> : > When bouncing pages, allow a new option to preserve the intra-page >> : > offset. This is needed for the ehci hardware buffer rings that >> : > assume >> : > this behavior. >> : >> : I thought we ended up with always doing that? >> : >> : Bounce buffers may or may not be used, so if the page offset >> : must be zero for bounce buffers, they must be zero for the >> : original DMA request. I see no value in re-aligning the DMA >> : request to a page boundary when bounce buffers are used, but >> : it is required in some cases to not realign. Hence, why not >> : always (and unconditionally) preserve the alignment? >> >> I'm not entirely sure either. However, at this stage of the game I'd >> rather be a little conservative in what we change and do a more >> careful and thorough analysis. > > Fair enough. > Busdma allows you to request bouncing for realignment. Unconditionally preserving the page offset when bouncing defeats this. Also, it has never preserved the offset. I have no idea if this was intentional or not. Scott