Date: Sun, 08 Feb 2009 18:00:05 -0700 From: Scott Long <scottl@samsco.org> To: Marcel Moolenaar <xcllnt@mac.com> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, "M. Warner Losh" <imp@bsdimp.com> Subject: Re: svn commit: r188350 - in head/sys: amd64/amd64 arm/arm dev/usb2/core i386/i386 ia64/ia64 sys Message-ID: <498F8015.8000704@samsco.org> In-Reply-To: <34EFBA0C-FB99-42DB-BF5C-A889348AD393@mac.com> 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>
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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 <xcllnt@mac.com> 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
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