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From:   Jacopo Mondi <jacopo+renesas@jmondi.org>
To:     kieran.bingham+renesas@ideasonboard.com,
        laurent.pinchart+renesas@ideasonboard.com,
        niklas.soderlund+renesas@ragnatech.se, geert@linux-m68k.org
Cc:     Jacopo Mondi <jacopo+renesas@jmondi.org>,
        linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Hyun Kwon <hyunk@xilinx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Subject: [PATCH v4 2/8] dt-bindings: media: max9286: Document 'maxim,,initial-reverse-channel-mV"
Date:   Thu, 12 Nov 2020 17:27:23 +0100
Message-Id: <20201112162729.101384-3-jacopo+renesas@jmondi.org>
In-Reply-To: <20201112162729.101384-1-jacopo+renesas@jmondi.org>
References: <20201112162729.101384-1-jacopo+renesas@jmondi.org>
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Document the 'initial-reverse-channel-mV' vendor property in the
bindings document of the max9286 driver.

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

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
---
 .../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..c506a0261325 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,initial-reverse-channel-mV:
+    $ref: '/schemas/types.yaml#/definitions/uint32'
+    minimum: 30
+    maximum: 200
+    default: 170
+    description: |
+      Initial amplitude of the reverse control channel, in millivolts.
+
+      The initial amplitude shall be adjusted to a value compatible with the
+      configuration of the connected remote serializer.
+
+      Some camera modules (in 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 170mV.
+
+      A typical value for the reverse channel amplitude to communicate with
+      a remote serializer whose high-threshold noise immunity is not enabled
+      is 100mV.
+
   ports:
     type: object
     description: |
@@ -221,6 +241,7 @@ required:
   - ports
   - i2c-mux
   - gpio-controller
+  - maxim,initial-reverse-channel-mV
 
 additionalProperties: false
 
@@ -243,6 +264,8 @@ examples:
         gpio-controller;
         #gpio-cells = <2>;
 
+        maxim,initial-reverse-channel-mV = <170>;
+
         ports {
           #address-cells = <1>;
           #size-cells = <0>;
-- 
2.29.1