[PATCH 12/20] dt-bindings: usb: dwc3: Add Tx De-emphasis restrictions

[Serge Semin]

In accordance with the driver comments the PIPE3 de-emphasis can be tuned
to be either -6dB, -2.5dB or disabled. Let's add the de-emphasis
property restriction so the DT schema would make sure the controller DT
node is equipped with correct value.

Signed-off-by: Serge Semin <Sergey.Semin at baikalelectronics.ru>

---

Changelog v2:
- Grammar fix: "s/tunned/tuned"
- Grammar fix: remove redundant "or" conjunction.
---
 Documentation/devicetree/bindings/usb/snps,dwc3.yaml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
index 2f746ac64e71..307affb669aa 100644
--- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
+++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
@@ -145,6 +145,10 @@ properties:
       The value driven to the PHY is controlled by the LTSSM during USB3
       Compliance mode.
     $ref: /schemas/types.yaml#/definitions/uint8
+    enum:
+      - 0 # -6dB de-emphasis
+      - 1 # -3.5dB de-emphasis
+      - 2 # No de-emphasis
 
   snps,dis_u3_susphy_quirk:
     description: When set core will disable USB3 suspend phy
-- 
2.27.0