atomicity in linked streams

[Takashi Iwai <tiwai@suse.de>]

Hi,

so far, some pcm operator callbacks are assumed to be atomic.
but looking at the code, this restriction seems coming only from the
rwlock of linked streams.

there are some hardwares which need (idally) the non-atomic operations
for prepare and trigger.  they usually require the ack as the command
completion.  and we implemented it in the busy loop or by ignoring the
ack.

i think the stream-link lock can be replaced with rw_semaphore, so
that prepare and trigger callbacks can be non-atomic.  the only
critical part is, as far as i see, that  snd_pcm_stop() may be called
from interrupt handler when  xrun/suspend happens.  this cannot handle
the semaphore, of course.

i have still no concrete idea how to solve this...  any suggestions?


btw, if the trigger can take too long time, we should implement this
into two seprate parts: the trigger and the post-trigger.  the trigger
would be issued and return immediately, and the post-trigger would
take care of the completion of commands.


Takashi


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