dt-bindings: rtc: qcom-pm8xxx: add uefi-variable offset

On many Qualcomm platforms the PMIC RTC control and time registers are
read-only so that the RTC time can not be updated. Instead an offset
needs be stored in some machine-specific non-volatile memory, which a
driver can take into account.

On platforms where the offset is stored in a Qualcomm specific UEFI
variable the variables are also accessed in a non-standard way, which
means that the OS cannot assume that the variable service is available
by the time the RTC driver probes.

Add a 'qcom,uefi-rtc-info' boolean flag to indicate that the RTC offset
is stored in a Qualcomm specific UEFI variable so that the OS can
determine whether to wait for it to become available.

The UEFI variable is

	882f8c2-9646-435f-8de5-f208ff80c1bd-RTCInfo

and holds a 12-byte structure where the first four bytes is a GPS time
offset in little-endian byte order.

Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Johan Hovold <[email protected]>
Acked-by: Rob Herring (Arm) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexandre Belloni <[email protected]>

Author: jhovold

Documentation/devicetree/bindings/rtc/qcom-pm8xxx-rtc.yaml

@@ -55,6 +55,12 @@ properties:
     description:
       RTC alarm is not owned by the OS
 
+  qcom,uefi-rtc-info:
+    type: boolean
+    description:
+      RTC offset is stored as a four-byte GPS time offset in a 12-byte UEFI
+      variable 882f8c2b-9646-435f-8de5-f208ff80c1bd-RTCInfo
+
   wakeup-source: true
 
 required: