Apply URT_010 feedback from ARC

Signed-off-by: Andrei Warkentin <andrei.warkentin@intel.com>

non-normative/uefi.adoc

@@ -33,3 +33,12 @@ register maps. In the cases where there are unpopulated PCIe slots
 behind a root bridge, `EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL_CONFIGURATION`
 reports valid resources assigned (e.g. for hot plug), or reports no
 resources assigned.
+
+[[uefi-guidance-rt]]
+==== UEFI Runtime Services
+
+Systems without an RTC and with an equivalent alternate source for current time,
+that is not trivially accessible from a UEFI implementation after the
+UEFI boot services are shut down (e.g. network time), can implement `GetTime()`
+using the `time` CSR. The time, of course, needs to be synchronized
+before the boot services are shut down.

uefi.adoc

@@ -63,10 +63,11 @@ See additional <<uefi-rt, requirements for UEFI runtime services>>.
 [%header, cols="5,25"]
 |===
 | ID#     ^| Requirement
-| `URT_010` a| Systems without a Real-Time Clock (RTC) MUST meet the following requirements:
+| `URT_010` a| Systems without a Real-Time Clock (RTC), but with an equivalent alternate source for the current time, MUST meet the following requirements:
 
-             * `GetTime()` MUST be implemented (e.g. in terms of CPU cycle counter).
+             * `GetTime()` MUST be implemented.
              * `SetTime()` MUST return `EFI_UNSUPPORTED`, and be appropriately described in the `EFI_RT_PROPERTIES_TABLE`.
+2+| _<<uefi-guidance-rt, See additional guidance>>_.
 | [[uefi-rtc]] `URT_020` a| Systems with a Real-Time Clock on an OS-managed bus (e.g. I2C, subject to arbitration issues due to access to the bus by the OS) MUST meet the following requirements:
 
              * `GetTime()` and `SetTime()` MUST return `EFI_UNSUPPORTED`, when called after the UEFI boot services have been exited.