gh it still may
be desirable to power manage the parent itself (e.g. by manipulating
its clock).

In general, device PM QoS may be used to address this problem.
Namely, if the device's children added PM QoS latency constraints
for it, they would be able to prevent it from being put into an
overly deep low-power state.  However, in some cases the devices
needing to be serviced are not the immediate children of a
"children-ignoring" device, but its grandchildren or even less
direct descendants.  In those cases, the entity wanting to add a
PM QoS request for a given device's ancestor that ignores its
children will have to find it in the first place, so introduce a new
helper function that may be used to achieve that.  This function,
dev_pm_qos_add_ancestor_request(), will search for the first
ancestor of the given device whose power.ignore_children flag is
set and will add a device PM QoS latency request for that ancestor
on behalf of the caller.  The request added this way may be removed
with the help of dev_pm_qos_remove_request() in the future, like
any other device PM QoS latency request.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
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