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().
Signed-off-by: Takashi Iwai tiwai@suse.de --- .../kernel-api/writing-an-alsa-driver.rst | 18 ++++++++++++++++-- 1 file 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 -----------