"Aneesh Kumar K.V (IBM)" [off-list ref] writes:

Nathan Lynch via B4 Relay [off-list ref]
writes:

quoted

Use the function lock API to prevent interleaving call sequences of
the ibm,activate-firmware RTAS function, which typically requires
multiple calls to complete the update. While the spec does not
specifically prohibit interleaved sequences, there's almost certainly
no advantage to allowing them.

Can we document what is the equivalent thing the userspace does?

I'm not sure what we would document.

As best I can tell, the activate_firmware command in powerpc-utils does
not make any effort to protect its use of the ibm,activate-firmware RTAS
function. The command is not intended to be run manually and I guess
it's relying on the platform's management console to serialize its
invocations.

drmgr (also from powerpc-utils) has some dead code for LPM that calls
ibm,activate-firmware; it should probably be removed. The command uses a
lock file to serialize all of its executions.

Something that could happen with interleaved ibm,activate-firmware
sequences is something like this:

1. Process A initiates an ibm,activate-firmware sequence and receives a
   "retry" status (-2/990x).
2. Process B calls ibm,activate-firmware and receives the "done" status
   (0), concluding the sequence A began.
3. Process A, unaware of B, calls ibm,activate-firmware again,
   inadvertently beginning a new sequence.

Seems mostly benign to me except that process A could fail to make
progress indefinitely under the right circumstances.