Re: cx18: "missing audio" for analog recordings

[Mark Lord <mlord@pobox.com>]

On 14/04/10 12:32 AM, Mark Lord wrote:
..
> The syslog shows the usual "fallback" messages,
> but the audio consisted of very loud static, the kind
> of noise one gets when the sample bits are all reversed.
>
> While it was failing, I tried retuning, stopping/starting
> the recording, etc.. nothing mattered. It wanted a reload
> of the cx18 driver to cure it.
..

Since all of this happens rather randomly,
I'm beginning to more strongly suspect a race condition
somewhere in the driver.

Now, it's a rather large driver -- lots of complexity in that chip
-- so it will take me a while to sort through things.

But at first blush, I don't see any obvious locking around
the various read-modify-write sequences for the audio registers.

And a quick "grep spin *.[ch]" shows a few spin_lock/spin_unlock
calls in cx18-queue.c and cx18-stream.c (as well as the alsa code,
which shouldn't be in play in this scenario).

Oddly, none of those spinlocks use _irq or _irq_save/restore,
which means they aren't providing any sort of mutual exclusion
against the interrupt handler.

But like I said, I'm only just beginning to look more closely now.
-- 
Mark Lord
Real-Time Remedies Inc.
mlord@pobox.com