ASoC: dt-bindings: add TDM slot idle mode properties

Add properties to describe TDM slot idle behaviour. These properties can
be used to describe how a DAI is supposed to behave when not active.

For example, Apple Silicon laptops split a single I2S bus between two
physical lines which are combined at an OR gate in front of the
receiving port. One codec on each line is expected to transmit zeroes
during the active TDM slots of the opposite line, or we will have corrupted
data at the receiver.

Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260301-tdm-idle-slots-v3-3-c6ac5351489a@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/tdm-slot.yaml

@@ -20,6 +20,20 @@ properties:
     $ref: /schemas/types.yaml#/definitions/uint32
     description: Width, in bits, of each slot
 
+  dai-tdm-idle-mode:
+    $ref: /schemas/types.yaml#/definitions/string
+    enum:
+      - none
+      - off
+      - zero
+      - pulldown
+      - hiz
+      - pullup
+      - drivehigh
+    description: Drive mode for inactive/idle TDM slots. For hardware that
+      implements .set_tdm_idle(). Optional. "None" represents undefined
+      behaviour and is the same as not setting this property.
+
 patternProperties:
   '^dai-tdm-slot-[rt]x-mask$':
     $ref: /schemas/types.yaml#/definitions/uint32-array
@@ -30,4 +44,9 @@ patternProperties:
       a mask. The first element of the array is slot 0 (LSB). Any nonzero
       value will be treated as 1.
 
+  '^dai-tdm-slot-[rt]x-idle-mask$':
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Idle slot mask. Optional. A bit being set to 1 indicates
+      that the corresponding TDM slot is inactive/idle.
+
 additionalProperties: true