dt-bindings: display: Add a property to deal with WiFi coexistence

The RaspberryPi4 has both a WiFi chip and HDMI outputs capable of doing
4k. Unfortunately, the 1440p resolution at 60Hz has a TMDS rate on the
HDMI cable right in the middle of the first Wifi channel.

Add a property to our HDMI controller, that could be reused by other
similar HDMI controllers, to allow the OS to take whatever measure is
necessary to avoid that crosstalk.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201029134018.1948636-1-maxime@cerno.tech

Documentation/devicetree/bindings/display/brcm,bcm2711-hdmi.yaml

@@ -76,6 +76,12 @@ properties:
   resets:
     maxItems: 1
 
+  wifi-2.4ghz-coexistence:
+    type: boolean
+    description: >
+      Should the pixel frequencies in the WiFi frequencies range be
+      avoided?
+
 required:
   - compatible
   - reg