linux-imx

ALSA: ca0106: Disable IZD on SB0570 DAC to fix audio pops

The Creative Audigy SE (SB0570) card currently exhibits an audible pop
whenever playback is stopped or resumed, or during silent periods of an
audio stream. Initialise the IZD bit to the 0 to eliminate these pops.

The Infinite Zero Detection (IZD) feature on the DAC causes the output
to be shunted to Vcap after 2048 samples of silence. This discharges the
AC coupling capacitor through the output and causes the aforementioned
pop/click noise.

The behaviour of the IZD bit is described on page 15 of the WM8768GEDS
datasheet: "With IZD=1, applying MUTE for 1024 consecutive input samples
will cause all outputs to be connected directly to VCAP. This also
happens if 2048 consecutive zero input samples are applied to all 6
channels, and IZD=0. It will be removed as soon as any channel receives
a non-zero input". I believe the second sentence might be referring to
IZD=1 instead of IZD=0 given the observed behaviour of the card.

This change should make the DAC initialisation consistent with
Creative's Windows driver, as this popping persists when initialising
the card in Linux and soft rebooting into Windows, but is not present on
a cold boot to Windows.

Signed-off-by: Alex Stanoev <alex@astanoev.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>