summaryrefslogtreecommitdiffstats
path: root/Documentation/sound
diff options
context:
space:
mode:
authorTakashi Iwai <tiwai@suse.de>2023-03-23 07:52:37 +0100
committerTakashi Iwai <tiwai@suse.de>2023-03-24 14:52:59 +0100
commit03f62c9cefdb833ab77bfef63066e923696dac0f (patch)
tree318d4b3d8fd6d7ce9776f1272e5bf8882cf4037e /Documentation/sound
parentf84af109f6ca6eba5fd3031cb5b85907a607b2b3 (diff)
downloadlinux-stable-03f62c9cefdb833ab77bfef63066e923696dac0f.tar.gz
linux-stable-03f62c9cefdb833ab77bfef63066e923696dac0f.tar.bz2
linux-stable-03f62c9cefdb833ab77bfef63066e923696dac0f.zip
ALSA: docs: A few more words for PCM XRUN handling and stream locks
Enhance the documents about the PCM, missing descriptions for a couple of helpers like snd_pcm_period_elapsed_under_stream_lock() and snd_pcm_stop_xrun(). Link: https://lore.kernel.org/r/20230323065237.5062-4-tiwai@suse.de Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'Documentation/sound')
-rw-r--r--Documentation/sound/kernel-api/writing-an-alsa-driver.rst18
1 files changed, 16 insertions, 2 deletions
diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
index 6b8f3495407f..a368529e8ed3 100644
--- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
+++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
@@ -2215,6 +2215,12 @@ Typical code would be like:
return IRQ_HANDLED;
}
+Also, when the device can detect a buffer underrun/overrun, the driver
+can notify the XRUN status to the PCM core by calling
+:c:func:`snd_pcm_stop_xrun()`. This function stops the stream and sets
+the PCM state to ``SNDRV_PCM_STATE_XRUN``. Note that it must be called
+outside the PCM stream lock, hence it can't be called from the atomic
+callback.
High frequency timer interrupts
@@ -2294,8 +2300,9 @@ mutexes or semaphores instead.
As already seen, some pcm callbacks are atomic and some are not. For
example, the ``hw_params`` callback is non-atomic, while ``trigger``
callback is atomic. This means, the latter is called already in a
-spinlock held by the PCM middle layer. Please take this atomicity into
-account when you choose a locking scheme in the callbacks.
+spinlock held by the PCM middle layer, the PCM stream lock. Please
+take this atomicity into account when you choose a locking scheme in
+the callbacks.
In the atomic callbacks, you cannot use functions which may call
:c:func:`schedule()` or go to :c:func:`sleep()`. Semaphores and
@@ -2318,6 +2325,13 @@ in the PCM core instead of spin and rwlocks, so that you can call all PCM
functions safely in a non-atomic
context.
+Also, in some cases, you might need to call
+:c:func:`snd_pcm_period_elapsed()` in the atomic context (e.g. the
+period gets elapsed during ``ack`` or other callback). There is a
+variant that can be called inside the PCM stream lock
+:c:func:`snd_pcm_period_elapsed_under_stream_lock()` for that purpose,
+too.
+
Constraints
-----------