Comment # 21 on bug 800701 from Hans Hu

For snd-hda-intel, current patch replaced set_memory_wc with
set_pages_array_wc. Function set_pages_array_wc marked the PTE of the original
buffer address; Function set_memory_wc marked the PTE both original and after
vmaped buffer address. Howerver, cache or not in transmission process is based
on the PTE of the later, and the set_pages_array_wc did���t mark it, so a cache
inconsistency issue occurs.

To prove, please use command "aplay -D plughw:0,0 44100_S16_LE_2c.wav" with
HDAC in non-snoop mode and you can hear it.

For now I can���t reappearance the Oops described before, so I don't how to
resolve them both, it needs developer's help.