[alsa-devel] no period wakeup support

[Jaroslav Kysela]

Dne 30. 01. 20 v 8:06 Takashi Sakamoto napsal(a):
> 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

I agree. We should not break the basic part of the API.

					Jaroslav

-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.