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Message-Id: <20071016203300.3f5bf599.akpm@linux-foundation.org> Date: Tue, 16 Oct 2007 20:33:00 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: akepner@....com Cc: Tony Luck <tony.luck@...el.com>, Grant Grundler <grundler@...isc-linux.org>, Jesse Barnes <jbarnes@...tuousgeek.org>, Jes Sorensen <jes@....com>, Randy Dunlap <randy.dunlap@...cle.com>, Roland Dreier <rdreier@...co.com>, James Bottomley <James.Bottomley@...eleye.com>, David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 3/3] document dma_flags_set/get_*() On Tue, 16 Oct 2007 18:44:17 -0700 akepner@....com wrote: > @@ -547,3 +547,41 @@ size is the size (and should be a page-sized multiple). > The return value will be either a pointer to the processor virtual > address of the memory, or an error (via PTR_ERR()) if any part of the > region is occupied. > + > +int > +dma_flags_set_attr(u32 attr, enum dma_data_direction dir) > + > +Amend dir with a platform-specific "dma attribute". > + > +The only attribute currently defined is DMA_BARRIER_ATTR, which causes > +in-flight DMA to be flushed when the associated memory region is written > +to (see example below). Setting DMA_BARRIER_ATTR provides a mechanism > +to enforce ordering of DMA on platforms that permit DMA to be reordered > +between device and host memory (within a NUMA interconnect). On other > +platforms this is a nop. > + > +DMA_BARRIER_ATTR would be set when the memory region is mapped for DMA, > +e.g.: > + > + int count; > + int flags = dma_flags_set_attr(DMA_BARRIER_ATTR, DMA_BIDIRECTIONAL); > + .... > + count = dma_map_sg(dev, sglist, nents, flags); > + Isn't this rather a kludge? What would be the cost of doing this cleanly and either redefining dma_data_direction to be a field-of-bits or just leave dma_data_direction alone (it is quite unrelated to this work, isn't it?) and adding new fields/arguments to manage this new functionality? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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