ALSA: pcm: Simplify snd_pcm_action_lock_irq()

The function snd_pcm_action_lock_irq() can be much simplified by
simply wrapping snd_pcm_action() with the stream lock.  This was
rather the original idea, but later it was open coded for
optimization.  However, looking at the optimization part closely, one
notices that the probability of the optimized path is quite low; in
normal situations, the linked stream action happens only for the
triggered substream, thus the operation becomes identical.  So the
code simplification has a clear win, especially because we have now
doubly codes for both atomic and non-atomic locks.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
ALSA: pcm: Refactoring snd_pcm_action()

Just a small code refactoring to reduce more lines.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
ALSA: pcm: Correct PCM BUG error message

While converting to dev_*(), the message showing the invalid PCM
position was wrongly tagged as if an XRUN although it's actually a
BUG.  This patch corrects the message again.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
ALSA: pcm: Replace PCM hwptr tracking with tracepoints

ALSA PCM core has a mechanism tracking the PCM hwptr updates for
analyzing XRUNs.  But its log is limited (up to 10) and its log output
is a kernel message, which is hard to handle.

In this patch, the hwptr logging is moved to the tracing
infrastructure instead of its own.  Not only the hwptr updates but
also XRUN and hwptr errors are recorded on the trace log, so that user
can see such events at the exact timing.

The new "snd_pcm" entry will appear in the tracing events:
  # ls -F /sys/kernel/debug/tracing/events/snd_pcm
  enable  filter  hw_ptr_error/  hwptr/  xrun/

The hwptr is for the regular hwptr update events.  An event trace
looks like:

  aplay-26187 [004] d..3  4012.834761: hwptr: pcmC0D0p/sub0: POS: pos=488, old=0, base=0, period=1024, buf=16384

"POS" shows the hwptr update by the explicit position update call and
"IRQ" means the hwptr update by the interrupt,
i.e. snd_pcm_period_elapsed() call.  The "pos" is the passed
ring-buffer offset by the caller, "old" is the previous hwptr, "base"
is the hwptr base position, "period" and "buf" are period- and
buffer-size of the target PCM substream.
(Note that the hwptr position displayed here isn't the ring-buffer
 offset.  It increments up to the PCM position boundary.)

The XRUN event appears similarly, but without "pos" field.
The hwptr error events appear with the PCM identifier and its reason
string, such as "Lost interrupt?".

The XRUN and hwptr error reports on kernel message are still left, can
be turned on/off via xrun_debug proc like before.  But the bit 3, 4, 5
and 6 bits of xrun_debug proc are dropped by this patch.  Also, along
with the change, the message strings have been reformatted to be a bit
more consistent.

Last but not least, the hwptr reporting is enabled only when
CONFIG_SND_PCM_XRUN_DEBUG is set.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
ALSA: pcm: Add xrun_injection proc entry

This patch adds a new proc entry for PCM substreams to inject an
XRUN.  When a PCM substream is running and any value is written to its
xrun_injection proc file, the driver triggers XRUN.  This is a useful
feature for debugging XRUN and error handling code paths.

Note that this entry is enabled only when CONFIG_SND_PCM_XRUN_DEBUG is
set.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Merge branch 'topic/pcm-locking' into for-next

here is a small series of patches for cleaning up / enhancing the
PCM core stuff.
Merge branch 'for-next'