dt-bindings: watchdog: Add support for TI K3 RTI watchdog

TI K3 SoCs contain an RTI (Real Time Interrupt) module which can be
used to implement a windowed watchdog functionality. Windowed watchdog
will generate an error if it is petted outside the time window, either
too early or too late.

Cc: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200312095808.19907-2-t-kristo@ti.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/ti,rti-wdt.yaml

@@ -0,0 +1,65 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/watchdog/ti,rti-wdt.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Texas Instruments K3 SoC Watchdog Timer
+
+maintainers:
+  - Tero Kristo <t-kristo@ti.com>
+
+description:
+  The TI K3 SoC watchdog timer is implemented via the RTI (Real Time
+  Interrupt) IP module. This timer adds a support for windowed watchdog
+  mode, which will signal an error if it is pinged outside the watchdog
+  time window, meaning either too early or too late. The error signal
+  generated can be routed to either interrupt a safety controller or
+  to directly reset the SoC.
+
+allOf:
+  - $ref: "watchdog.yaml#"
+
+properties:
+  compatible:
+    enum:
+      - ti,j7-rti-wdt
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  power-domains:
+    maxItems: 1
+
+  assigned-clocks:
+    maxItems: 1
+
+  assigned-clocks-parents:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - power-domains
+
+examples:
+  - |
+    /*
+     * RTI WDT in main domain on J721e SoC. Assigned clocks are used to
+     * select the source clock for the watchdog, forcing it to tick with
+     * a 32kHz clock in this case.
+     */
+    #include <dt-bindings/soc/ti,sci_pm_domain.h>
+
+    watchdog0: rti@2200000 {
+        compatible = "ti,rti-wdt";
+        reg = <0x0 0x2200000 0x0 0x100>;
+        clocks = <&k3_clks 252 1>;
+        power-domains = <&k3_pds 252 TI_SCI_PD_EXCLUSIVE>;
+        assigned-clocks = <&k3_clks 252 1>;
+        assigned-clock-parents = <&k3_clks 252 5>;
+    };