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Request for comments: relaxing time services requirements #167

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38 changes: 34 additions & 4 deletions source/chapter2-uefi.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -519,16 +519,16 @@ are required to be implemented during boot services and runtime services.
- Before `ExitBootServices()`
- After `ExitBootServices()`
* - `GetTime`
- Required if RTC present.
- Required if RTC present. [#TimeNote]_
- Optional
* - `SetTime`
- Required if RTC present.
- Required if RTC present. [#TimeNote]_
- Optional
* - `GetWakeupTime`
- Required if wakeup supported.
- Required if wakeup supported. [#TimeNote]_
- Optional
* - `SetWakeupTime`
- Required if wakeup supported.
- Required if wakeup supported. [#TimeNote]_
- Optional
* - `SetVirtualAddressMap`
- N/A
Expand Down Expand Up @@ -561,6 +561,9 @@ are required to be implemented during boot services and runtime services.
- Optional
- Optional

.. [#TimeNote] See section :ref:`section-rtc` for relaxed requirements on time
services.

Runtime Device Mappings
-----------------------

Expand All @@ -579,6 +582,8 @@ shall not be accessed by the OS.
Only devices that explicitly support concurrent access by both firmware and an
OS may be mapped at runtime by both firmware and the OS.

.. _section-rtc:

Real-time Clock (RTC)
^^^^^^^^^^^^^^^^^^^^^

Expand All @@ -594,6 +599,31 @@ However, if firmware does not support access to the RTC after
`ExitBootServices()`, then `GetTime()` and `SetTime()` shall return
`EFI_UNSUPPORTED` and the OS must use a device driver to control the RTC.

.. versionchanged:: 3.0.0

Some further aspects of the Services defined in :UEFI:`8.3` are made optional.
[#RelaxNote]_

.. [#RelaxNote] Those relaxations allow to support Time Services with a timer
instead of a real-time clock.

Firmware may behave as if some fields of all the `EFI_TIME` structures had fixed
values, as listed in the following table:

.. list-table:: Optional `EFI_TIME` structure fields fixed values
:widths: 50 50
:header-rows: 1

* - `EFI_TIME` structure field
- Optional fixed value
* - `TimeZone`
- `EFI_UNSPECIFIED_TIMEZONE`
* - `Daylight`
- 0

Firmware is also not required to persist the current local time and date or the
system wakeup alarm clock time information across reset.
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@xypron xypron May 20, 2026

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The problem in U-Boot is not persistence. There is no support in the hardware driver framework at all for wakeup times though the hardware support might exist.

So the current suggestion won't help to make U-Boot compliant.

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@vstehle vstehle May 20, 2026

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Hi @xypron,

Thanks for the review.

For wakeup we are somewhat covered already as those services are only conditionally required:

EFI_RUNTIME_SERVICES function Before ExitBootServices() After ExitBootServices()
.. .. ..
GetWakeupTime Required if wakeup supported. Optional
SetWakeupTime Required if wakeup supported. Optional

Persistence of e.g. time or daylight settings is still a small issue here, I think, as it is indeed tested by the SCT and it will not work on platforms using RTC emulation.


UEFI Reset and Shutdown
-----------------------

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