[PATCH 2/3] dt-bindings: display: rk3588-dw-hdmi-qp: Document enable-gpios property

[Laurent Pinchart]

The RK3588 DW HDMI QP encoder only supports AC-coupled links as defined
by the HDMI 2.1 FRL mode. In order to be compliant with the DC common
mode requirements of HDMI 2.0 (and earlier) TMDS mode, the middle point
of the termination resistors needs to be connected to ground. Document a
property to toggle this connection using a GPIO.

The property could be better named, but it has been introduced in the
Linux kernel driver for this device a year ago in commit 128a9bf8ace2
("drm/rockchip: Add basic RK3588 HDMI output support"). While it is not
used by any in-tree device tree, it may be used in the wild.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 .../bindings/display/rockchip/rockchip,rk3588-dw-hdmi-qp.yaml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/rockchip/rockchip,rk3588-dw-hdmi-qp.yaml b/Documentation/devicetree/bindings/display/rockchip/rockchip,rk3588-dw-hdmi-qp.yaml
index 96b4b088eebe..7471c2f51c32 100644
--- a/Documentation/devicetree/bindings/display/rockchip/rockchip,rk3588-dw-hdmi-qp.yaml
+++ b/Documentation/devicetree/bindings/display/rockchip/rockchip,rk3588-dw-hdmi-qp.yaml
@@ -103,6 +103,10 @@ properties:
   "#sound-dai-cells":
     const: 0
 
+  enable-gpios:
+    description:
+      GPIO to switch between TMDS (when active) and FRS (when inactive) modes.
+
   rockchip,grf:
     $ref: /schemas/types.yaml#/definitions/phandle
     description:
-- 
Regards,

Laurent Pinchart