linux-kernel - [PATCH v6 2/5] dt-bindings: media: max9286: Document 'maxim,reverse-channel-microvolt'

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Date:   Tue, 15 Dec 2020 18:09:54 +0100
From:   Jacopo Mondi <jacopo+renesas@...ndi.org>
To:     kieran.bingham+renesas@...asonboard.com,
        laurent.pinchart+renesas@...asonboard.com,
        niklas.soderlund+renesas@...natech.se, geert@...ux-m68k.org,
        robh@...nel.org, devicetree@...r.kernel.org
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hyun Kwon <hyunk@...inx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        sergei.shtylyov@...il.com
Subject: [PATCH v6 2/5] dt-bindings: media: max9286: Document 'maxim,reverse-channel-microvolt'

Document the 'reverse-channel-microvolt' vendor property in the
bindings document of the max9286 driver.

The newly introduced property allows to specifying the initial
configuration of the GMSL reverse control channel to accommodate
remote serializers pre-programmed with the high threshold power
supply noise immunity enabled.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
---
v5->v6:
- Use standard unit suffix 'microvolt' for the custom property
- Drop '$ref' as according to 'example-schema.yaml':
  "Vendor specific properties having a standard unit suffix don't need a type."
---
 .../bindings/media/i2c/maxim,max9286.yaml     | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml b/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml
index 9ea827092fdd..b22ba3e0db4a 100644
--- a/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml
+++ b/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml
@@ -51,6 +51,26 @@ properties:
   '#gpio-cells':
     const: 2

+  maxim,reverse-channel-microvolt:
+    minimum: 30000
+    maximum: 200000
+    default: 170000
+    description: |
+      Initial amplitude of the reverse control channel, in micro volts.
+
+      The initial amplitude shall be adjusted to a value compatible with the
+      configuration of the connected remote serializer.
+
+      Some camera modules (for example RDACM20) include an on-board MCU that
+      pre-programs the embedded serializer with power supply noise immunity
+      (high-threshold) enabled. A typical value of the deserializer's reverse
+      channel amplitude to communicate with pre-programmed serializers is
+      170000 micro volts.
+
+      A typical value for the reverse channel amplitude to communicate with
+      a remote serializer whose high-threshold noise immunity is not enabled
+      is 100000 micro volts
+
   ports:
     type: object
     description: |
@@ -221,6 +241,7 @@ required:
   - ports
   - i2c-mux
   - gpio-controller
+  - maxim,reverse-channel-microvolt

 additionalProperties: false

@@ -243,6 +264,8 @@ examples:
         gpio-controller;
         #gpio-cells = <2>;

+        maxim,reverse-channel-microvolt = <170000>;
+
         ports {
           #address-cells = <1>;
           #size-cells = <0>;
--
2.29.2