Date: Sun, 16 Nov 2008 14:08:20 +0100 From: Hans Petter Selasky <hselasky@c2i.net> To: freebsd-usb@freebsd.org Cc: freebsd-current@freebsd.org Subject: Re: [Serious] busdma bug in -current in relation to USB hardware - review wanted Message-ID: <200811161408.21562.hselasky@c2i.net> In-Reply-To: <200811081023.10058.hselasky@freebsd.org> References: <20081107082740.GA1334@icarus.home.lan> <20081108001128.GA1437@icarus.home.lan> <200811081023.10058.hselasky@freebsd.org>
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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 */ Without this new feature in busdma the USB hardware will not work when the DMA data is placed on bounce pages, for example on 64-bit architectures with more than 4GB of RAM. --HPS
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