[PATCH] ALSA: hda/hdmi: Add Intel silent stream support

[Jaroslav Kysela]

Dne 24. 06. 20 v 9:45 Takashi Iwai napsal(a):
> On Wed, 24 Jun 2020 01:26:36 +0200,
> Harsha Priya wrote:
>>
>> External HDMI receivers have analog circuitry that needs to be powered-on
>> when exiting standby, and a mechanism to detect PCM v. IEC61937 data.
>> These two steps take time and up to 2-3 seconds of audio may be muted
>> when starting playback.
>>
>> Intel hardware can keep the link active with a 'silent stream', so that
>> the receiver does not go through those two steps when valid audio is
>> transmitted. This mechanism relies on an info packet and preventing the
>> codec from going to D3, which will increase the platform static power
>> consumption. The info packet assumes a basic 2ch stereo, and the silent
>> stream is enabled when connecting a monitor. In case of format changes the
>> detection of PCM v. IEC61937 needs to be re-run. In this case there is no
>> way to avoid the 2-3s mute.
>>
>> The silent stream is enabled with a Kconfig option, as well as a kernel
>> parameter should there be a need to override the build time default.
> 
> I'm not sure whether the module option is the best interface.
> An alternative is a mixer element that controls dynamically.  Then
> it'll be per card unlike the module option.

+1, kcontrol seems the appropriate way to control this.

				Jaroslav

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