tree c2a319d7a5198e9f2bc726790e57679300dfaf05
parent 3c72b2ab0b21e502d6b7d52b494f82313a8739cf
author Boyan Karatotev <boyan.karatotev@arm.com> 1732197359 +0000
committer Boyan Karatotev <boyan.karatotev@arm.com> 1734362070 +0000

fix(spe): add a psb before updating context and remove context saving

In the chapter about FEAT_SPE (D16.4 specifically) it is stated that
"Sampling is always disabled at EL3". That means that disabling sampling
(writing PMBLIMITR_EL1.E to 0) is redundant and can be removed. The only
reason we save/restore SPE context is because of that disable, so those
can be removed too.

There's the issue of draining the profiling buffer though. No new
samples will have been generated since entering EL3. However, old
samples might still be in-flight. Unless synchronised by a psb csync,
those might be affected by our extensive context mutation. Adding a psb
in prepare_el3_entry should cater for that. Note that prior to the
introduction of root context this was not a problem as context remained
unchanged and the hooks took care of the rest.

Then, the only time we care about the buffer actually making it to
memory is when we exit coherency. On HW_ASSISTED_COHERENCY systems we
don't have to do anything, it should be handled for us. Systems without
it need a dsb to wait for them to complete. There should be one already
in each cpu's powerdown hook which should work.

While on the topic of barriers, the esb barrier is no longer used.
Remove it.

Change-Id: I9736fc7d109702c63e7d403dc9e2a4272828afb2
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>