[coreboot] [RFC] How to add “nested” time stamps?

[Julius Werner]

We have kinda already added some cases like this so I hope nobody has
big objections to it. For example, you'll usually see
TS_START_ULZMA/TS_END_ULZMA in between TS_START_COPYRAM/TS_END_COPYRAM
so you can differentiate the transfer and decompression components of
loading the ramstage.

I don't think there are restrictions for choosing numbers apart from
what's already written in code comments in timestamp_serialized.h
(e.g. 1000+ is for payloads, 500-1000 is for vendor extensions, in
particular 500-600 Chrome OS and 950-1000 Intel). If you're adding
timestamps that will always fall between TS_DEVICE_INITIALIZE (60) and
TS_DEVICE_DONE (70), it would probably make sense to allocate them
from the range in between (e.g. 61, 62). (In general, we should
probably try to keep "generic coreboot" timestamps within 0-100 for
now so we keep 100-400 free for potential future sections we want to
add.)

Otherwise, I'd say feel free to add as many timestamps as you think
will add value. You just have to be careful that you don't risk
exceeding the available space on any board. I think that's current 84
timestamps for the total boot (shouldn't be too hard to increase if
necessary), with additional restrictions for pre-RAM environments and
super-early ramstage before CBMEM init.