[alsa-devel] [PATCH] ASoC: dmaengine: add runtime status checking in dmaengine_pcm_dma_complete

Lars-Peter Clausen lars at metafoo.de
Wed Jun 12 14:15:24 CEST 2013

On 06/12/2013 09:43 AM, Vinod Koul wrote:
> On Mon, Jun 10, 2013 at 12:46:52PM +0200, Lars-Peter Clausen wrote:
>> On 06/10/2013 11:31 AM, Mark Brown wrote:
>>> On Sun, Jun 09, 2013 at 03:51:09PM +0200, Lars-Peter Clausen wrote:
>>>> On 06/09/2013 03:37 PM, Lars-Peter Clausen wrote:
>>>>> I haven't see the original patch, but the proper solution to this problem
>>>>> should be to add a check to snd_dmaengine_pcm_close() to see if the DMA is
>>>>> still running.
>>>> Ok, since this will never happen, I suppose the problem is rather that the DMA
>>>> callback is called after dma_terminate_all() has been called. Which sounds like
>>>> it is a bug in the dmaengine driver. And this will likely also be a problem for
>>>> other users of that dmaengine driver and not only the ASoC driver, so it should
>>>> be fixed in the dmaengine driver.
>>> Just to clarify what is it makes you say that this will never happen?
>> At least that is my understanding of snd_pcm_release_substream(), that it
>> will first make sure that the stream is stopped, by calling snd_pcm_drop(),
>> before closing the stream.
> Yes you need to call dmaengine_terminate_all(). But even then we might have
> trasaction in flight or some dma controllers cant abort immediately (need to
> wait till FIFOs are flushed etc). In general it is a good practice to call
> dma_sync_wait() before you tear down the client.
> If you still see an issue, then it a buggy driver :)

Even though if the driver can't abort the transfer immediately, I'd still
expect to not see any calls to the descriptors callback after
dmaengine_terminate_all() has been called.

We should probably still call dma_sync_wait() though before we free any of
the DMA transfer buffers. But I guess this will open a whole new can of
bugs, since none of the drivers actually seem to mark a descriptor as
completed if the transfer is aborted using dmaengine_terminate_all()

- Lars

More information about the Alsa-devel mailing list