linux-kernel - Re: dmaengine cyclic transfers

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Date:	Tue, 10 Aug 2010 23:17:40 +0200
From:	Linus Walleij <linus.ml.walleij@...il.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Hans-Christian Egtvedt <hans-christian.egtvedt@...el.com>
Subject: Re: dmaengine cyclic transfers

2010/8/10 Sascha Hauer <s.hauer@...gutronix.de>:

> Author: Hans-Christian Egtvedt <hans-christian.egtvedt@...el.com>
> Date:   Wed Apr 1 15:47:02 2009 +0200
>
>    dw_dmac: add cyclic API to DW DMA driver
>
> This could be very useful for the SDMA engine aswell. What are the
> reasons this is not implemented in the generic dmaengine API but as
> an extension to a specific driver?

No reasons what I know. There was a similar code snippet in Peter
Pearse's PL08x driver as well, I just didn't know what to do with it.

> Should I also implement it like
> this or isn't it better to extend the dmaengine itself?

This is going to be generally useful, so please extend the DMAengine
if I have my say. I actually miss two functions from the engine:

1) Single buffer slave transfers (without sglist)
2) Cyclic buffers (esp good for audio)

The first I have a patch for, will repost.

Yours,
Linus Walleij
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