drc_isolate_logical() is used to move the DRC from the "Configured" to
the "Available" state, erroring out if the DRC is in the unexpected
"Unisolate" state and doing nothing (with RTAS_OUT_SUCCESS) if the DRC
is already in "Available" or in "Unusable" state.

When moving from "Configured" to "Available", the DRC is moved to the
LOGICAL_AVAILABLE state, a drc->unplug_requested check is done and, if
true, spapr_drc_detach() is called.

What spapr_drc_detach() does then is:

- set drc->unplug_requested to true. In fact, this is the only place
where unplug_request is set to true;
- does nothing else if drc->state != drck->empty_state. If the DRC
state is equal to drck->empty_state, spapr_drc_release() is
called. For logical DRCs, drck->empty_state = LOGICAL_UNUSABLE.

In short, calling spapr_drc_detach() in drc_isolate_logical() does
nothing. It'll set unplug_request to true again ('again' since it was
already true - otherwise the function wouldn't be called), and will
return without calling spapr_drc_release() because the DRC is not in
LOGICAL_UNUSABLE, since drc_isolate_logical() just moved it to
LOGICAL_AVAILABLE. The only place where the logical DRC is released is
when called from drc_set_unusable(), when it is moved to the
"Unusable" state.  As it should, according to PAPR.

Even though calling spapr_drc_detach() in drc_isolate_logical() is
benign, removing it will avoid further thought about the matter. So
let's go ahead and do that.

As a note, this logic was introduced in commit bbf5c878. Since
then, the DRC handling code was refactored and enhanced, and PAPR
itself went through some changes in the DRC area as well. It is
expected that some assumptions we had back then are now deprecated.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20210211225246.17315-2-danielhb413@gmail.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>