[RFC v3 07/12] dt-bindings: gpio: Add hardware-timestamp-engine property

[Dipen Patel <dipenp@nvidia.com>]

Some GPIO controllers can timestamp GPIO lines in real time using
hardware timestamp engine. The optional property is added to facilitate
this feature.

The nvidia GPIO controller has hardware timestamp engine as a backend
to timestamp its GPIO lines in a real time. This change set adds
hardware-timestamp-engine property to reflect that fact.

Signed-off-by: Dipen Patel <dipenp@nvidia.com>
---
 Documentation/devicetree/bindings/gpio/gpio.txt           | 8 ++++++++
 .../devicetree/bindings/gpio/nvidia,tegra186-gpio.txt     | 7 +++++++
 2 files changed, 15 insertions(+)

diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index a8895d339bfe..c6ae2eaf5762 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -167,6 +167,13 @@ left to right from the passed array. An incomplete array (where the number
 of passed named are less than ngpios) will still be used up until the last
 provided valid line index.
 
+Optionally, a GPIO controller may have a "hardware-timestamp-engine" property.
+This specifies the timestamp engine node. The property is only useful if the
+hardware timestamp engine (HTE) serves as a back-end to support hardware
+timestamp GPIO lines in a real time and GPIO controller has dependency on the
+engine. It will be up to GPIO controller and HTE provider drivers to figure out
+the mapping between GPIO controller and HTE namespaces of a given GPIO line.
+
 Example:
 
 gpio-controller@00000000 {
@@ -180,6 +187,7 @@ gpio-controller@00000000 {
 		"LED G", "LED B", "Col A", "Col B", "Col C", "Col D",
 		"Row A", "Row B", "Row C", "Row D", "NMI button",
 		"poweroff", "reset";
+	hardware-timestamp-engine = <&hadrware_ts_engine_node>;
 }
 
 The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
diff --git a/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt b/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt
index adff16c71d21..20f6c9e69839 100644
--- a/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt
@@ -127,6 +127,12 @@ Required properties:
             - 8: Active low level-sensitive.
             Valid combinations are 1, 2, 3, 4, 8.
 
+Optional properties:
+- hardware-timestamp-engine
+    AON GPIO controller has timestamp engine which can hardware timestamp
+    GPIO configured as input and IRQ. This property specifies hardware
+    timestamp engine (HTE) device-tree node.
+
 Example:
 
 #include <dt-bindings/interrupt-controller/irq.h>
@@ -162,4 +168,5 @@ gpio@c2f0000 {
 	#gpio-cells = <2>;
 	interrupt-controller;
 	#interrupt-cells = <2>;
+	hardware-timestamp-engine = <&tegra_hte_aon>;
 };
-- 
2.17.1