[PATCH v3] ALSA: hda/hdmi: Add Intel silent stream support

[Takashi Iwai]

On Mon, 06 Jul 2020 22:53:17 +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 (Haswell and beyond) 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 setting the channel_id as 0xf, sending 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.
> This approach is used based on the power_save capability as an example,
> but in the future, it may be used with a kcontrol,
> depending on UCM support for HDaudio legacy.
> 
> Signed-off-by: Harsha Priya <harshapriya.n at intel.com>
> Signed-off-by: Emmanuel Jillela <emmanuel.jillela at intel.com>
> Reviewed-by: Kai Vehmanen <kai.vehmanen at linux.intel.com>
> Reported-by: kernel test robot <lkp at intel.com>

Applied now to for-next branch.  Thanks.


Takashi