[PATCH 1/2] dt-bindings: serial: stm32: add fifo threshold configuration

[Erwan Le Ray <erwan.leray@foss.st.com>]

Add two optional DT properties, to configure RX and TX fifo threshold:
- st,rx-fifo-threshold-bytes
- st,tx-fifo-threshold-bytes

This patch depends on patch ("dt-bindings: serial: Add rx-tx-swap to stm32-usart").

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>

diff --git a/Documentation/devicetree/bindings/serial/st,stm32-uart.yaml b/Documentation/devicetree/bindings/serial/st,stm32-uart.yaml
index c69f8464cdf3..e163449bf39e 100644
--- a/Documentation/devicetree/bindings/serial/st,stm32-uart.yaml
+++ b/Documentation/devicetree/bindings/serial/st,stm32-uart.yaml
@@ -65,6 +65,22 @@ properties:
   linux,rs485-enabled-at-boot-time: true
   rs485-rx-during-tx: true
 
+  st,rx-fifo-threshold-bytes:
+    description:
+      RX FIFO threshold configuration in bytes.
+      If value is set to 1, RX FIFO threshold is disabled.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    enum: [1, 2, 4, 8, 12, 14, 16]
+    default: 8
+
+  st,tx-fifo-threshold-bytes:
+    description:
+      TX FIFO threshold configuration in bytes.
+      If value is set to 1, TX FIFO threshold is disabled.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    enum: [1, 2, 4, 8, 12, 14, 16]
+    default: 8
+
 allOf:
   - $ref: rs485.yaml#
   - $ref: serial.yaml#
@@ -82,6 +98,17 @@ allOf:
     then:
       properties:
         rx-tx-swap: false
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - st,stm32-uart
+              - st,stm32f7-uart
+    then:
+      properties:
+        st,rx-fifo-threshold-bytes: false
+        st,tx-fifo-threshold-bytes: false
 
 required:
   - compatible
@@ -96,13 +123,15 @@ examples:
   - |
     #include <dt-bindings/clock/stm32mp1-clks.h>
     usart1: serial@40011000 {
-      compatible = "st,stm32-uart";
+      compatible = "st,stm32h7-uart";
       reg = <0x40011000 0x400>;
       interrupts = <37>;
       clocks = <&rcc 0 164>;
       dmas = <&dma2 2 4 0x414 0x0>,
              <&dma2 7 4 0x414 0x0>;
       dma-names = "rx", "tx";
+      st,rx-fifo-threshold-bytes = <4>;
+      st,tx-fifo-threshold-bytes = <4>;
       rs485-rts-active-low;
     };
 
-- 
2.17.1