• Harsha Priya's avatar
    ALSA: hda/hdmi: Add Intel silent stream support · 951894cf
    Harsha Priya authored
    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: default avatarHarsha Priya <harshapriya.n@intel.com>
    Signed-off-by: default avatarEmmanuel Jillela <emmanuel.jillela@intel.com>
    Reviewed-by: default avatarKai Vehmanen <kai.vehmanen@linux.intel.com>
    Reported-by: default avatarkernel test robot <lkp@intel.com>
    Link: https://lore.kernel.org/r/1594068797-14011-1-git-send-email-harshapriya.n@intel.comSigned-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    951894cf
Kconfig 8.16 KB