[RFC] Pass reset reason to Linux via FDT

["Sverdlin, Alexander" <alexander.sverdlin@siemens.com>]

Dear Device Tree Spec Team!

I would like to receive your opinion on the new /chosen/reset-reason property
I would like to introduce in the spec and consequently in the U-Boot.

I've posted an U-Boot patchset [1] with the proposed implementation which
would work on TI K3 SoCs initially.

- Do you think I need to send a formal patch to device tree spec?
- Do you think /chosen/reset-reason is the proper location for the SoC/platform
  agnostic reset cause information?
- Do you think having an opaque string there is OK, bearing in mind that there
  is no standard approach up to now to this topic, neither in Linux nor in
  U-Boot, taking into account different SoCs and vendors provide very different
  information regarding reset cause, which is barely possible to unify?

The proposed change would look like following:

diff --git a/dtschema/schemas/chosen.yaml b/dtschema/schemas/chosen.yaml
index 63f3c12..d908426 100644
--- a/dtschema/schemas/chosen.yaml
+++ b/dtschema/schemas/chosen.yaml
@@ -183,6 +183,20 @@ properties:
       will assign devices in its usual manner, otherwise it will not try to
       assign devices and instead use them as they are configured already.
 
+  reset-reason:
+    $ref: types.yaml#/definitions/string
+    description:
+      This property is set by the bootloader to indicate the reason for the
+      most recent system reset, e.g. "POR" (power-on reset), "WDOG" (watchdog),
+      "PIN" (external reset pin), "RST" (software warm reset), "THERMAL", etc.
+      The set of possible values is platform-specific.
+
+      / {
+              chosen {
+                      reset-reason = "WDOG";
+              };
+      };
+
   smbios3-entrypoint:
     $ref: types.yaml#/definitions/address
     maxItems: 1

[1] https://www.mail-archive.com/u-boot@lists.denx.de/msg573811.html

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com