[PATCH 6/7] dt-bindings: serial: max310x: Add maxim,tristate-when-closed

[Tapio Reijonen]

The MAX310x UARTs can three-state TX and RTS per channel. Add a
per-channel flag asking for that whenever the port is not open, for
boards where the outputs must stay undriven then: a driven output
would back-feed an unpowered part behind the pins, or fight another
device driving the line.

Signed-off-by: Tapio Reijonen <tapio.reijonen@xxxxxxxxxxx>
---
 .../devicetree/bindings/serial/maxim,max310x.yaml        | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/serial/maxim,max310x.yaml b/Documentation/devicetree/bindings/serial/maxim,max310x.yaml
index e598dda4d13f514820ed8012f2fb2fc2aba3e669..f54296f6b6c85e3a6246e210af9ea8ee6af5118b 100644
--- a/Documentation/devicetree/bindings/serial/maxim,max310x.yaml
+++ b/Documentation/devicetree/bindings/serial/maxim,max310x.yaml
@@ -54,6 +54,16 @@ required:
   - clocks
   - clock-names
 
+$defs:
+  maxim,tristate-when-closed:
+    $ref: /schemas/types.yaml#/definitions/flag
+    description:
+      Three-state the channel's TX and RTS outputs whenever the port is
+      not open, from probe until the first open and after each close.
+      For boards where a driven output would back-feed an unpowered part
+      behind the pins, or where another device drives the line while the
+      port is closed. The board defines the levels the outputs float to.
+
 allOf:
   - $ref: /schemas/spi/spi-peripheral-props.yaml#
 
@@ -68,6 +78,9 @@ allOf:
       allOf:
         - $ref: /schemas/serial/serial.yaml#
         - $ref: /schemas/serial/rs485.yaml#
+      properties:
+        maxim,tristate-when-closed:
+          $ref: "#/$defs/maxim,tristate-when-closed"
 
   - if:
       properties:
@@ -93,6 +106,8 @@ allOf:
             reg:
               description: UART channel number on the chip.
               maximum: 3
+            maxim,tristate-when-closed:
+              $ref: "#/$defs/maxim,tristate-when-closed"
           required:
             - reg
           unevaluatedProperties: false
@@ -156,6 +171,7 @@ examples:
 
             serial@2 {
                 reg = <2>;
+                maxim,tristate-when-closed;
                 rs485-rts-active-low;
             };
         };

-- 
2.47.3