linux-kernel - Re: [PATCH 2/3] dma: override "dma_flags_set

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Date:	Tue, 21 Aug 2007 13:05:15 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	akepner@....com
Cc:	Jes Sorensen <jes@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>, rdreier@...co.com,
	linux-ia64 <linux-ia64@...r.kernel.org>,
	James.Bottomley@...senPartnership.com
Subject: Re: [PATCH 2/3] dma: override "dma_flags_set_dmaflush" for sn-ia64

On Tue, 21 Aug 2007 12:35:22 -0700 akepner@....com wrote:

> 
> > I'm a little concerned about changing the API for the dma_ foo
> > functions, which are defined cross platform. If you want to change
> > that, I think it will require updating the documentation explaining
> > it.....
> 
> What do you think of the following? (And is there anyone else 
> I should be cc-ing for review?)

probably the document's author (cc added)


> Document semantics of dma_flags_set_dmaflush()
> 
> Signed-off-by: Arthur Kepner <akepner@....com>
> --
>  DMA-API.txt |   22 ++++++++++++++++++++++
>  1 files changed, 22 insertions(+)
> 
> diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
> index cc7a8c3..e117b72 100644
> --- a/Documentation/DMA-API.txt
> +++ b/Documentation/DMA-API.txt
> @@ -392,6 +392,28 @@ Notes:  You must do this:
>  
>  See also dma_map_single().
>  
> +int
> +dma_flags_set_dmaflush(int dir)
> +
> +Amend dir (one of the enum dma_data_direction values), with a platform-

no comma.

> +specific "dmaflush" attribute. Unless the platform supports "posted DMA" 

add comma after "posted DMA" and drop lots of trailing spaces.

> +this is a no-op. 
> +
> +On platforms that support posted DMA, dma_flags_set_dmaflush() causes 
> +device writes to the associated memory region to flush in-flight DMA. 
> +This can be important, for example, when (DMA) writes to the memory 
> +region indicate that DMA of data is complete. If DMA of data and DMA of 
> +the completion indication race, as they can do when the platform supports 
> +posted DMA, then the completion indication may arrive in host memory 
> +ahead of some data.
> +
> +To prevent this, you might map the memory region used for completion 
> +indications as follows:
> +
> +	int count, flags = dma_flags_set_dmaflush(DMA_BIDIRECTIONAL);
> +	.....
> +	count = dma_map_sg(dev, sglist, nents, flags);
> +
>  
>  Part II - Advanced dma_ usage
>  -----------------------------
> -- 
> Arthur


---
~Randy
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