[alsa-devel] no period wakeup support

[Takashi Sakamoto]

On Wed, Jan 29, 2020 at 05:43:19PM -0600, Pierre-Louis Bossart wrote:
> > Nowadays, is this reasonable to consider disabling the period wakeup as default
> > instead of expecting period wakeup by default?
> 
> I'd say yes - it's been nearly 10 years since this capability was added, and
> it's quite common across HDaudio, Chrome, Android plaforms.
> 
> But considering this as a default doesn't mean it's available in 100% of the
> cases, you still you need to check that
> 
> a) the driver is capable of disabling the period wakeup
> b) the driver is capable of providing a precise position outside of period
> elapsed events (usually marked with the INFO_BATCH capability).
> 
> alsa-lib gives you the means to query both cases.
> 
> Note that you also have the case where you cannot disable interrupts but can
> still use timer-based solutions (e.g. for USB audio).

I suspect this advice.

In design of ALSA PCM core, runtime of PCM substream is configured for
the mode of no-period-wakeup just in a case that userspace application
requests it[1].

As long as developers take enough care of compatibility for existent
applications, it's better to support period wakeup for each IRQ as a
default, then support no-period-wakeup mode as an option.


[1] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/tree/sound/core/pcm_native.c#n715

Regards

Takashi Sakamoto