[regression] snd_hda and "channel dead"

Hi,

I'm having a problem with sound via hda driver.  After a while of playing 
sound it stops with:

pcm0: chn_write(): pcm0:virtual:dsp0.vp0: play interrupt timeout, channel dead

showing up in dmesg.  After that no sound is played and Amarok skips through 
tracks quickly (it "plays" sounds to fast)...

After setting dev.hdac.0.polling=1 sound works again.  

This is with a custom kernel that has sound compiled in and without debugging 
options.  

A known good kernel is from ~ 13 May while the bad kernel is ~ 1 day old.  

Some further information:
# dmesg | grep hdac
hdac0: <NVidia MCP51 High Definition Audio Controller> mem 0xe7000000-0xe7003fff 
irq 21 at device 16.1 on pci0
hdac0: HDA Driver Revision: 20100226_0142
hdac0: [ITHREAD]
hdac0: HDA Codec #0: Realtek ALC888
pcm0: <HDA Realtek ALC888 PCM #0 Analog> at cad 0 nid 1 on hdac0
pcm1: <HDA Realtek ALC888 PCM #1 Analog> at cad 0 nid 1 on hdac0
pcm2: <HDA Realtek ALC888 PCM #2 Digital> at cad 0 nid 1 on hdac0
hdac0: <NVidia MCP51 High Definition Audio Controller> mem 0xe7000000-0xe7003fff 
irq 21 at device 16.1 on pci0
hdac0: HDA Driver Revision: 20100226_0142
hdac0: [ITHREAD]
hdac0: HDA Codec #0: Realtek ALC888
pcm0: <HDA Realtek ALC888 PCM #0 Analog> at cad 0 nid 1 on hdac0
pcm1: <HDA Realtek ALC888 PCM #1 Analog> at cad 0 nid 1 on hdac0
pcm2: <HDA Realtek ALC888 PCM #2 Digital> at cad 0 nid 1 on hdac0

and

# grep '^C.*FLAGS' /etc/make.conf
CFLAGS+= -DNDEBUG

Is there anything I can do to assist diagnostics?

Regards,

David