• Takashi Iwai's avatar
    ALSA: usb-audio: Add "Keep Interface" control · 4120fbed
    Takashi Iwai authored
    This patch adds "Keep Interface" control for each USB-audio device.
    The control element is with SND_CTL_IFACE_CARD, so that it won't
    appear on any sane mixer applications.  For a device that is confirmed
    to work well with "keep-interface" mode, user can flip the control via
    amixer, e.g.
      % amixer -c1 cset iface=CARD,name='Keep Interface' on
    
    and save/restore the state via alsactl.
    
    The reason to provide this via control API is that the behavior must
    be pretty depending on the device (and the firmware in it), so it's
    not ideal to apply via module option.
    
    For a device that certainly works, we may set it statically via a
    quirk table entry.  But a device like Dell WD15 dock behaves so
    differently depending on the firmware, and we can't set it
    statically.  So leave this as a dynamic switch each user can adjust
    freely.
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    4120fbed
mixer.c 79.8 KB