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From: Takashi Iwai <>
To: Andrew Gabbasov <>
Cc: <>, <>,
	"Jaroslav Kysela" <>, Takashi Iwai <>,
	Timo Wischer <>
Subject: Re: [PATCH v3 0/7] ALSA: aloop: Support sound timer as clock source instead of jiffies
Date: Thu, 14 Nov 2019 18:10:57 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Mon, 11 Nov 2019 12:08:39 +0100,
Andrew Gabbasov wrote:
> This patch set is an updated version of patches by Timo Wischer:
> This patch set is required for forwarding audio data between a HW sound
> card and an aloop device without the usage of an asynchronous sample rate
> converter.
> Most of sound and timers related code is kept the same as in previous set.
> The code, related to snd_pcm_link() functionality and its using for
> timer source setting, is removed (as rejected earlier). The changes in this
> update are mainly related to the parameters handling and some cleanup.
> The timer source can be initially selected by "timer_source" kernel module
> parameter. It is supposed to have the following format:
>     [<pref>:](<card name>|<card idx>)[{.,}<dev idx>[{.,}<subdev idx>]]
> For example: "hw:I82801AAICH.1.0", or "1.1", or just "I82801AAICH".
> (Prefix is ignored, just allowed here to be able to use the strings,
> the user got used to).
> Although the parsing function recognizes both '.' and ',' as a separator,
> module parameters handling routines use ',' to separate parameters for
> different module instances (array elements), so we have to use '.'
> to separate device and subdevice numbers from the card name or number
> in module parameters.
> Empty string indicates using jiffies as a timer source.
> Besides "static" selection of timer source at module load time,
> it is possible to dynamically change it via sound "info" interface
> (using "/proc/asound/<card>/timer_source" file in read-write mode.
> The contents of this file is used as a timer source string for
> a particular loopback card, e.g. "hw:0,0,0" (and here ',' can be used
> as a separator).
> The timer source string value can be changed at any time, but it is
> latched by PCM substream open callback "loopback_open()" (the first
> one for a particular cable). At this point it is actually used,
> that is the string is parsed, and the timer is looked up and opened.
> This seems to be a good trade-off between flexibility of updates and
> synchronizations or racing complexity.
> The timer source is set for a loopback card (the same as initial setting
> by module parameter), but every cable uses the value, current at the moment
> of opening. Theoretically, it's possible to set the timer source for each
> cable independently (via separate files), but it would be inconsistent
> with the initial setting via module parameters on a per-card basis.
> v2:
> v3:
> - Change sound card lookup to use snd_card_ref() and avoid direct access
>   to sound cards array
> - Squash commits on returning error codes for timer start and stop
> - Some locking related fixes
> - Some code cleanup

The patch won't work with the latest ALSA timer code found in my
for-next branch due to the API changes.  Essentially you need to
rewrite as:
	timeri = snd_timer_instance_new(...);
	if (!timeri)
	timeri->flags |= ...;
	timeri->ccallback = ...;
	err = snd_timer_open(timeri, ....);
	if (err < 0)



  parent reply	other threads:[~2019-11-14 17:11 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-11 11:08 Andrew Gabbasov
2019-11-11 11:08 ` [PATCH v3 1/7] ALSA: aloop: Describe units of variables Andrew Gabbasov
2019-11-11 11:08   ` [PATCH v3 2/7] ALSA: aloop: Support return of error code for timer start and stop Andrew Gabbasov
2019-11-11 11:08     ` [PATCH v3 3/7] ALSA: aloop: Use callback functions for timer specific implementations Andrew Gabbasov
2019-11-11 11:08       ` [PATCH v3 4/7] ALSA: aloop: Rename all jiffies timer specific functions Andrew Gabbasov
2019-11-11 11:08         ` [PATCH v3 5/7] ALSA: aloop: Move CABLE_VALID_BOTH to the top of file Andrew Gabbasov
2019-11-11 11:08           ` [PATCH v3 6/7] ALSA: aloop: Support selection of snd_timer instead of jiffies Andrew Gabbasov
2019-11-11 11:08             ` [PATCH v3 7/7] ALSA: aloop: Support runtime change of snd_timer via info interface Andrew Gabbasov
2019-11-14 17:10 ` Takashi Iwai [this message]
2019-11-20 12:15   ` [PATCH v3 0/7] ALSA: aloop: Support sound timer as clock source instead of jiffies Andrew Gabbasov

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