ASoC: samsung: midas-audio: Add GPIO-based headset

Merge series from Artur Weber <aweber.kernel@gmail.com>:

Many of Samsung's Exynos 4 devices share the same midas-audio driver
to handle the codec setup. While most of these devices, including the
Midas itself, use the jack detection provided by the WM8994 driver,
other devices such as the Samsung Galaxy Tab 3 8.0 (lt01) use two GPIOs
and an ADC channel to determine jack insertion, the jack's type, and
button presses (for headsets with volume up/down/play buttons).

In the downstream kernel, this behavior is implemented in the sec-jack
driver[1], and the per-device settings are configured in *-jack.c files
in the mach folder (see e.g. the Tab 3's implementation[2]).

This patchset implements this mechanism in the midas_wm1811.c driver,
and adds new DTS options to allow for its configuration. It also
enables jack detection for the Samsung Galaxy Tab 3 8.0.

A very similar mechanism was already present in the aries_wm8994.c
driver[3]; this implementation heavily borrows from it, though there
are a few extra cleanups as well.

Documentation/devicetree/bindings/sound/samsung,midas-audio.yaml

@@ -53,6 +53,9 @@ properties:
   submic-bias-supply:
     description: Supply for the micbias on the Sub microphone
 
+  headset-mic-bias-supply:
+    description: Supply for the micbias on the Headset microphone
+
   fm-sel-gpios:
     maxItems: 1
     description: GPIO pin for FM selection
@@ -61,6 +64,36 @@ properties:
     maxItems: 1
     description: GPIO pin for line out selection
 
+  headset-detect-gpios:
+    maxItems: 1
+    description: GPIO for detection of headset insertion
+
+  headset-key-gpios:
+    maxItems: 1
+    description: GPIO for detection of headset key press
+
+  io-channels:
+    maxItems: 1
+    description: IO channel to read micbias voltage for headset detection
+
+  io-channel-names:
+    const: headset-detect
+
+  samsung,headset-4pole-threshold-microvolt:
+    minItems: 2
+    maxItems: 2
+    description:
+      Array containing minimum and maximum IO channel value for 4-pole
+      (with microphone/button) headsets. If the IO channel value is
+      outside of this range, a 3-pole headset is assumed.
+
+  samsung,headset-button-threshold-microvolt:
+    minItems: 3
+    maxItems: 3
+    description: |
+      Array of minimum (inclusive) IO channel values for headset button
+      detection, in order: "Media", "Volume Up" and "Volume Down".
+
 required:
   - compatible
   - cpu

sound/soc/samsung/Kconfig

@@ -140,7 +140,7 @@ config SND_SOC_SAMSUNG_ARIES_WM8994
 
 config SND_SOC_SAMSUNG_MIDAS_WM1811
 	tristate "SoC I2S Audio support for Midas boards"
-	depends on SND_SOC_SAMSUNG
+	depends on SND_SOC_SAMSUNG && IIO
 	select SND_SAMSUNG_I2S
 	select SND_SOC_WM8994
 	help