Messages in this thread | | | Date | Thu, 27 Sep 2007 21:33:26 -0600 | From | Grant Grundler <> | Subject | Re: [3/4] dma: document dma_flags_set_dmabarrier() |
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On Thu, Sep 27, 2007 at 06:13:02PM -0700, akepner@sgi.com wrote: > > Document dma_flags_set_dmabarrier(). > > Signed-off-by: Arthur Kepner <akepner@sgi.com>
This looks really good!
thanks, grant
Acked-by: Grant Grundler <grundler@parisc-linux.org>
> > --- > DMA-API.txt | 26 ++++++++++++++++++++++++++ > 1 files changed, 26 insertions(+) > > diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt > index cc7a8c3..5fc0bba 100644 > --- a/Documentation/DMA-API.txt > +++ b/Documentation/DMA-API.txt > @@ -544,3 +544,29 @@ 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_dmabarrier(int dir) > + > +Amend dir (one of the enum dma_data_direction values), with a > +platform-specific "dmabarrier" attribute. The dmabarrier attribute > +forces a flush of all in-flight DMA when the associated memory > +region is written to (see example below.) > + > +This 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. > + > +The dmabarrier would be set when the memory region is mapped for DMA, > +e.g.: > + > + int count, flags = dma_flags_set_dmabarrier(DMA_BIDIRECTIONAL); > + .... > + count = dma_map_sg(dev, sglist, nents, flags); > + > +As an example of a situation where this would be useful, suppose that > +the device does a DMA write to indicate that data is ready and > +available in memory. The DMA of the "completion indication" could > +race with data DMA. Using a dmabarrier on the memory used for > +completion indications would prevent the race. > + - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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