[PATCH v2] dt-bindings: dma: st-stm32-dmamux: Add description for dma-cell values

[Ken Sloat]

The dma-cell values for the stm32-dmamux are used to craft the DMA spec
for the actual controller. These values are currently undocumented
leaving the user to reverse engineer the driver in order to determine
their meaning. Add a basic description, while avoiding duplicating
information by pointing the user to the associated DMA docs that
describe the fields in depth.

Signed-off-by: Ken Sloat <ksloat at cornersoftsolutions.com>
---

Changes in v2:
    - Remove redundant comment regarding dma-cells val
    - Reference bindings doc for DMA controller

 .../devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml
index f26c914a3a9a..b7bca1a83769 100644
--- a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml
+++ b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml
@@ -15,6 +15,16 @@ allOf:
 properties:
   "#dma-cells":
     const: 3
+    description: |
+      Each cell represents the following:
+      1. The mux input number/line for the request
+      2. Bitfield representing DMA channel configuration that is passed
+         to the real DMA controller
+      3. Bitfield representing device dependent DMA features passed to
+         the real DMA controller
+
+      For bitfield definitions of cells 2 and 3, see the associated
+      bindings doc for the actual DMA controller in st,stm32-dma.yaml.
 
   compatible:
     const: st,stm32h7-dmamux
-- 
2.34.1