Date: Sun, 16 Nov 2008 11:12:10 -0800 From: Marcel Moolenaar <xcllnt@mac.com> To: Hans Petter Selasky <hselasky@c2i.net> Cc: freebsd-current@freebsd.org, freebsd-usb@freebsd.org Subject: Re: [Serious] busdma bug in -current in relation to USB hardware - review wanted Message-ID: <B7285D6E-520D-48D2-9287-824976138846@mac.com> In-Reply-To: <200811161408.21562.hselasky@c2i.net> References: <20081107082740.GA1334@icarus.home.lan> <20081108001128.GA1437@icarus.home.lan> <200811081023.10058.hselasky@freebsd.org> <200811161408.21562.hselasky@c2i.net>
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On Nov 16, 2008, at 5:08 AM, Hans Petter Selasky wrote: > Hi, > > It turns out my initial patch need to be limited to the use-case > only. Before > I start any real work, I want to know if anyone will object if I > implement > the following new BUS_DMA flag into FreeBSD's busdma system? > > amd64/amd64/busdma_machdep.c > i386/i386/busdma_machdep.c > arm/arm/busdma_machdep.c > ia64/ia64/busdma_machdep.c > mips/mips/busdma_machdep.c > powerpc/powerpc/busdma_machdep.c > sparc64/sparc64/bus_machdep.c > sun4v/sun4v/bus_machdep.c > sys/bus_dma.h > > /* > * The following flag specifies that no re-alignment of individual > * memory pages is allowed when loaded into DMA. It can only be used > * when "maxsegsz" is equal to "PAGE_SIZE" and "alignment" is less > * than or equal to 1. > * > * Background: Some kinds of DMA hardware only stores the full > * physical address of the first memory page when multiple memory > * pages are loaded into DMA. Consequtive memory pages only gets the > * non-offset part of the physical address updated. The hardware > * computes the amount of data that should be stored in the first > * memory page from the minimum of the total transfer length and > * PAGE_SIZE minus the initial page offset. When the initial page > * offset is not preserved the hardware ends up transferring an > * invalid number of bytes to or from the initial memory page. > */ > #define BUS_DMA_NOREAL 0x400 /* no page re-alignment allowed */ No objection, but please call it BUS_DMA_NOREALIGN NOREAL reads as NO-REAL and not as NO-RE-AL. And with real addressing an existing concept, confusion is not far around the corner... -- Marcel Moolenaar xcllnt@mac.com
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