[alsa-devel] ASoC:Question rate constraint between the dais

Clemens Ladisch clemens at ladisch.de
Sat Mar 17 14:00:57 CET 2012

Lars-Peter Clausen wrote:
> On 03/16/2012 08:25 PM, Mark Brown wrote:
>> On Thu, Mar 15, 2012 at 05:28:13PM -0400, Trent Piepho wrote:
>>> There is a race when the constraints change dynamically.  See the
>>> fsl_ssi.c driver and the sample size constraint in synchronous mode.
>> This is just a limitation of the ALSA ABI - there's nothing we can do
>> about it without changing the userspace interface so we just have to
>> live with it and error out if an application ever manages to hit the
>> race and pick something incompatible with other active streams (note
>> that the symmetric rates support has a dev_warn() complaining about
>> hitting the race).
> I think the real problem with this is, that currently a userspace application
> will usually exit with an error when such a race occurs, while it should be
> possible to just restart the enumeration process and try with another format.
> So I'm wondering if we can make it easier for userspace to detect that the
> constraints have changed and it may retry with other parameters?

Devices that have such a restriction must be marked with
SNDRV_PCM_INFO_JOINT_DUPLEX.  There is no indication that the race has
actually happened, so applications that care have to retry just in case.


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