Date: Mon, 09 Feb 2009 09:51:28 -0800 From: Marcel Moolenaar <xcllnt@mac.com> To: John Baldwin <jhb@freebsd.org> Cc: svn-src-head@freebsd.org, Scott Long <scottl@samsco.org>, src-committers@freebsd.org, svn-src-all@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: <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com> In-Reply-To: <200902090923.45887.jhb@freebsd.org> References: <200902082254.n18MsxVt037307@svn.freebsd.org> <498F8015.8000704@samsco.org> <94616FBD-4638-4C51-990C-06A943B1BA2A@mac.com> <200902090923.45887.jhb@freebsd.org>
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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
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