[alsa-devel] How to report error in _pointer function?

In my driver, I can detect in the _pointer callback function whether or not the DMA engine has actually started. Sometimes, when I have a programming error, the DMA will not start, so my _pointer function calculates a crazy value for the current position. The number it returns causes ALSA to go haywire (see my post titled, "underrun!!! (at least 1786051083.613 ms long)".

What is the best way to handle this? Is there a way I can tell ALSA, "hey, this is really screwed up, just abort playback and return an error to the app"?