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@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
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