Date: Mon, 09 Feb 2009 11:30:53 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: xcllnt@mac.com Cc: svn-src-head@freebsd.org, scottl@samsco.org, src-committers@freebsd.org, svn-src-all@freebsd.org, jhb@freebsd.org Subject: Re: svn commit: r188350 - in head/sys: amd64/amd64 arm/arm dev/usb2/core i386/i386 ia64/ia64 sys Message-ID: <20090209.113053.65361811.imp@bsdimp.com> In-Reply-To: <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com> References: <94616FBD-4638-4C51-990C-06A943B1BA2A@mac.com> <200902090923.45887.jhb@freebsd.org> <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com>
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In message: <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com>
Marcel Moolenaar <xcllnt@mac.com> 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
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