[alsa-devel] HDA record fails with FIFO error

[Takashi Iwai]

At Thu, 07 Apr 2011 16:30:00 +0200,
David Henningsson wrote:
> 
> On 2011-04-07 12:10, Takashi Iwai wrote:
> > At Thu, 7 Apr 2011 16:54:50 +0800,
> > Xu, Andiry wrote:
> >>
> >> Hi Takashi,
> >>
> >> Currently I encountered an HD audio issue reported by customer on a
> >> Lenovo x100e system. Sometimes, but not always, when starting a
> >> recording stream through the HDA controller, the controller generates a
> >> large amount of interrupts (~40 000 interrupts per second). After this
> >> has happened, jack sense (i e unsolicited events from the codec) stops
> >> working until the next system reboot.
> 
> This seems more reproducible now than it was a while ago, now it seems 
> to happen more often than not.
> 
> >> SD0STS returns a FIFO error (0x28) in interrupt handler. The interrupt
> >> service routine acknowledges this error but does not do anything to
> >> counteract the root cause to the problem, so it appears again and again.
> >> Restarting the stream does not seem to help. Enable MSI or not does not
> >> help either.
> >>
> >> The issue occurs on 2.6.35 and 2.6.38-rc8+, have not tried latest kernel
> >> yet but I think it's also there. FIFO error indicates FIFO overrun
> >> occurring while the RUN bit is set, but the driver simply acknowledge
> >> and clear the error. I wonder what the root cause and the right
> >> treatment are in this case. Any suggestions?
> 
> Brainstorming:
> 1) We could try adding udelays at random places.
> 2) There are a few workarounds for different chips already in 
> hda_intel.c, maybe try applying them here as well.
> 
> Does that make sense to either of you?

Hm, I don't think this would make any difference.  For the DMA engine,
it doesn't matter whether there is some delays in the code or not.
It's set up for the free-wheel run.  The driver just reads the current
position, but changes anything else than the buffer contents.
(And FIFO XRUN is irrelevant with the buffer contents.)


> > FIFO_ERR is actually never handled, so basically we can ignore.
> > Simply disabling it like below works around your problem?
> >
> > Of course, a proper handling of FIFO error would be better, but
> > this may need more code rewrites.
> 
> This does not fix the error in question, it removes the interrupts all 
> right, but neither recording nor jack sense starts to work.

Well, the unanswered question is why this interrupt is generated.
We don't know whether this interrupt is really correctly generated.
It might be wrongly triggered by some condition.  If so, masking and
ignoring the false error is the right fix, I guess.


Takashi