Date: Mon, 09 Feb 2009 11:00:54 -0800 From: Sam Leffler <sam@freebsd.org> To: Scott Long <scottl@samsco.org> Cc: src-committers@freebsd.org, jhb@freebsd.org, svn-src-all@freebsd.org, xcllnt@mac.com, svn-src-head@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: <49907D66.9010405@freebsd.org> In-Reply-To: <49907B32.8080307@samsco.org> References: <94616FBD-4638-4C51-990C-06A943B1BA2A@mac.com> <200902090923.45887.jhb@freebsd.org> <2EA5FEEB-E676-4D1B-9700-399C783F4590@mac.com> <20090209.113053.65361811.imp@bsdimp.com> <49907B32.8080307@samsco.org>
next in thread | previous in thread | raw e-mail | index | archive | help
Scott Long wrote: > M. Warner Losh wrote: >> 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 > > So yes, it's only available really on amd64 and i386 at the moment. > No reason why it can't be available elsewhere, and I'm working on > factoring > all of the bounce logic out into an MD file so it can be made available. > For architectures that use an IOMMU, there's probably no reason why > re-alignment can't use the IOMMU instead of bouncing. ARM does bounce buffers. Looks like it'll bounce for mis-aligned data. Sam
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?49907D66.9010405>