linux-kernel - Re: dmaengine: query current transfer status

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Date:	Mon, 11 Jan 2010 15:23:41 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	linux-kernel@...r.kernel.org,
	Maciej Sosnowski <maciej.sosnowski@...el.com>
Subject: Re: dmaengine: query current transfer status

On Mon, Jan 11, 2010 at 7:59 AM, Guennadi Liakhovetski
<g.liakhovetski@....de> wrote:
> Hi
>
> I'm using the dmaengine API with an ASoC driver (soon to be submitted),
> and I have to provide a callback to ALSA to query the progress of the
> current transfer (the .pointer() method from struct snd_pcm_ops).
> Currently I only can provide this information with a period size
> precision. Wouldn't it make sense to add an optional hook to dmaengine for
> that? I certainly could add this as a platform-specific extension to the
> specific dmaengine driver, I'm using (shdma), but that'd be ugly. Ideas?
> Specific proposals for the prototype? I could cook up a patch if there are
> no principal objections against this.

No principal objections, but we already have a method for querying the
status of a transaction ->device_is_tx_complete().  I'd rather change
the semantics of this method to return the inflight state of the
operation in addition to the channel's progress.  Perhaps pass in a
pointer to a new dma_tx_info (name?) struct that gets filled in with
the cookie information in addition to the current position of the
operation in question.

Something like:

struct dma_tx_info {
     dma_cookie_t last;
     dma_cookie_t used;
     unsigned long pos;
}

enum dma_status (*device_is_tx_complete)(struct dma_chan *chan,
dma_cookie_t cookie, struct dma_tx_info *info)

--
Dan
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