ASoC: dmic: Add optional wakeup delay

On some systems a delay is needed after switching on the clocks, to allow
the output to stabilize and avoid a popping noise at the beginning of
the recording. Add the optional device tree property 'wakeup-delay-ms'
and apply the specified delay after enabling the mic. A blocking delay
can't be applied in dmic_daiops_trigger() since the function is called
in atomic context. Instead use a DAPM event handler to set the enable
GPIO and apply the delay in the handler.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/sound/dmic.txt b/Documentation/devicetree/bindings/sound/dmic.txt
index f7bf65611453..e957b4136716 100644
--- a/Documentation/devicetree/bindings/sound/dmic.txt
+++ b/Documentation/devicetree/bindings/sound/dmic.txt
@@ -8,6 +8,7 @@ Required properties:
 Optional properties:
 	- dmicen-gpios: GPIO specifier for dmic to control start and stop
 	- num-channels: Number of microphones on this DAI
+	- wakeup-delay-ms: Delay (in ms) after enabling the DMIC
 
 Example node:
 
@@ -15,4 +16,5 @@ Example node:
 		compatible = "dmic-codec";
 		dmicen-gpios = <&gpio4 3 GPIO_ACTIVE_HIGH>;
 		num-channels = <1>;
+		wakeup-delay-ms <50>;
 	};