snd-pcsp driver takes chip->substream_lock together with PCM substream
lock. These are even mixed up with hrtimer's lock, resulting in messy
lock depencies. Right now, snd-pcsp driver resolves the deadlock by
using HRTIMER_CB_SOFTIRQ. However, this isn't nice for a really fast
path like bit-flipping.
This patch introduces a tasklet for PCM period handling so that the
hrtimer callback can be handled fast. This also reduce the use of
chip->substream_lock to avoid deadlocks. It's still used in pointer
callback, but even this could be removed with a proper barrier.
Another good solution is to introduce async trigger callback. But,
this will involve with a major rewrite of the PCM core code, so I
take first this easy fix.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
96c7d478ef