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From: "M. Warner Losh" <imp@bsdimp.com>
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Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org,
	src-committers@FreeBSD.org
Subject: Re: svn commit: r188350 - in head/sys: amd64/amd64 arm/arm
 dev/usb2/core i386/i386 ia64/ia64 sys
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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.  One area we do need to fix is the
inability to flush a subset of the range.

Warner