From: Jaroslav Kysela <perex@perex.cz>
To: Kai Vehmanen <kai.vehmanen@linux.intel.com>,
Takashi Iwai <tiwai@suse.de>
Cc: Pavel Hofman <pavel.hofman@ivitera.com>,
"alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>
Subject: Re: Functionality of pcm_notify in snd-aloop?
Date: Thu, 30 Apr 2020 14:17:56 +0200 [thread overview]
Message-ID: <f6fa39ec-9675-ce3c-c77e-3a438433ea6b@perex.cz> (raw)
In-Reply-To: <alpine.DEB.2.21.2004281910520.2957@eliteleevi.tm.intel.com>
Dne 28. 04. 20 v 18:19 Kai Vehmanen napsal(a):
> Hey,
>
> On Tue, 28 Apr 2020, Takashi Iwai wrote:
>
>> I believe the missing piece here is a generic way to tell user-space
>> that the stream got invalidated. This would be useful not only for
>> aloop but can be applied in general when a stream becomes temporarily
>> unavailable (e.g. the HDMI monitor disconnected or the DSP route
>> switched).
>
> ack on that. I've been preparing this patch to add -ENODATA to alsa-lib
> documentation:
> "[RFC] pcm: add documentation for -ENODATA error code handling"
> https://github.com/kv2019i/alsa-lib/commit/87b298106e04054489ee93b26a610e37f99a3171
>
> Have not yet had time to send a proper version to the list, but it's
> addressing specifically this need. This would serve as the interface for
> SOF DSP to tell that a given PCM node will not be providing data (as the
> DSP topology is not fully connected) [1].
>
> To test the above, I've used a small hack to aplay/arecord that keeps
> trying to restart the PCM after a delay, in case -ENODATA is returned:
> https://github.com/kv2019i/alsa-utils/commit/a2ba541ea0b3e86a65687de88a41f10cf0a8ddc2
This code calls wrongly snd_pcm_resume() here. Also, we should really think
about the whole mechanism when the stream cannot be activated (also for
playback - Intel HDMI LPE driver [2]). I mean that the poll multiplexer should
handle this state, too. If we don't find a way to notify the user space that
the stream can be started using the poll(), we can use another interface like
control API for the notifications.
We may also instroduce a new PCM state "WAIT" to wait on the hardware / link
availability (SETUP -> -ENODATA -> WAIT -> use poll() for the link status ->
success -> SETUP -> PREPARE) - talking about SNDRV_PCM_STATE states here.
Jaroslav
> [1] https://github.com/thesofproject/sof/issues/2564
[2]
https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/blob/36a4923f9bd05d4c5e2e8b1765f18edf452b9251/src/modules/alsa/module-alsa-card.c#L928-933
--
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
next prev parent reply other threads:[~2020-04-30 12:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-26 17:19 Functionality of pcm_notify in snd-aloop? Pavel Hofman
2020-03-26 17:44 ` Jaroslav Kysela
2020-03-26 17:59 ` Pavel Hofman
2020-03-30 14:43 ` Pavel Hofman
2020-03-30 15:09 ` Jaroslav Kysela
2020-03-31 15:07 ` Pavel Hofman
2020-04-28 15:44 ` Takashi Iwai
2020-04-28 16:19 ` Kai Vehmanen
2020-04-30 12:17 ` Jaroslav Kysela [this message]
2020-04-30 17:36 ` Kai Vehmanen
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