Re: dmaengine: query current transfer status

From: Dan Williams
Date: Mon Jan 11 2010 - 17:31:45 EST

On Mon, Jan 11, 2010 at 7:59 AM, Guennadi Liakhovetski
<g.liakhovetski@xxxxxx> 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)

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