[alsa-devel] [PATCH 2/6] ASoC/mpc5200: get rid of the appl_ptr tracking nonsense

[Mark Brown]

On 11 Nov 2009, at 19:24, Grant Likely <grant.likely at secretlab.ca>  
wrote:

> On Wed, Nov 11, 2009 at 11:37 AM, Mark Brown
> <broonie at opensource.wolfsonmicro.com> wrote:
>> On Wed, Nov 11, 2009 at 11:38:06AM -0500, Jon Smirl wrote:
>>>> Providing a final valid data point to the driver would possibly  
>>>> even
>>>> make things worse since if it were used then you'd have the  
>>>> equivalent
>>>> race where the application has initialized some data but not yet  
>>>> managed
>>>> to update the driver to tell it it's being handed over; if the  
>>>> driver
>>
>>> That's an under run condition.
>>
>> Yes, of course - the issue is that this approach encourages them,  
>> making
>> the system less robust if things are on the edge.  The mpc5200  
>> seems to
>> be not just on the edge but comfortably beyond it for some reason.
>
> I can't reproduce the issue at all as long at the dev_dbg() statement
> in the trigger stop path is disabled.  With it enabled, I hear the
> problem every time.  The 5200 may not be a speedy beast, but it is
> plenty fast enough to shut down the audio stream before stale data
> starts getting played out.

Yes, that does sound entirely consistent with the problem being a  
latency issue if you're sending the dev_dbg() output to the serial  
port. I'd be surprised if it were anything else to be honest.