Re: [3/4] dma: document dma_flags_set_dmabarrier()
From: Grant Grundler
Date: Thu Sep 27 2007 - 23:33:57 EST
On Thu, Sep 27, 2007 at 06:13:02PM -0700, akepner@xxxxxxx wrote:
> Document dma_flags_set_dmabarrier().
> Signed-off-by: Arthur Kepner <akepner@xxxxxxx>
This looks really good!
Acked-by: Grant Grundler <grundler@xxxxxxxxxxxxxxxx>
> 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.
> +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,
> + 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.
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