dt-bindings: watchdog: dw-wdt: Add watchdog TOPs array property

In case if DW Watchdog IP core is built with WDT_USE_FIX_TOP == false,
a custom timeout periods are used to preset the timer counter. In
this case that periods should be specified in a new "snps,watchdog-tops"
property of the DW watchdog dts node.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-mips@vger.kernel.org
Link: https://lore.kernel.org/r/20200530073557.22661-4-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/snps,dw-wdt.yaml

@@ -39,6 +39,23 @@ properties:
     description: Phandle to the DW Watchdog reset lane
     maxItems: 1
 
+  snps,watchdog-tops:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    description: |
+      DW APB Watchdog custom timer intervals - Timeout Period ranges (TOPs).
+      Each TOP is a number loaded into the watchdog counter at the moment of
+      the timer restart. The counter decrementing happens each tick of the
+      reference clock. Therefore the TOPs array is equivalent to an array of
+      the timer expiration intervals supported by the DW APB Watchdog. Note
+      DW APB Watchdog IP-core might be synthesized with fixed TOP values,
+      in which case this property is unnecessary with default TOPs utilized.
+    default: [0x0001000 0x0002000 0x0004000 0x0008000
+      0x0010000 0x0020000 0x0040000 0x0080000
+      0x0100000 0x0200000 0x0400000 0x0800000
+      0x1000000 0x2000000 0x4000000 0x8000000]
+    minItems: 16
+    maxItems: 16
+
 unevaluatedProperties: false
 
 required:
@@ -55,4 +72,19 @@ examples:
       clocks = <&per_base_clk>;
       resets = <&wdt_rst>;
     };
+
+  - |
+    watchdog@ffd02000 {
+      compatible = "snps,dw-wdt";
+      reg = <0xffd02000 0x1000>;
+      interrupts = <0 171 4>;
+      clocks = <&per_base_clk>;
+      clock-names = "tclk";
+      snps,watchdog-tops = <0x000000FF 0x000001FF 0x000003FF
+                            0x000007FF 0x0000FFFF 0x0001FFFF
+                            0x0003FFFF 0x0007FFFF 0x000FFFFF
+                            0x001FFFFF 0x003FFFFF 0x007FFFFF
+                            0x00FFFFFF 0x01FFFFFF 0x03FFFFFF
+                            0x07FFFFFF>;
+    };
 ...