The i915 display power is requested both by controller (for init
and link reset) as well as by codec driver (for codec control).

There's an additional constraint that on some platforms frequent changes
to display power state may cause visible flicker. To avoid this, the SOF
hda controller requests display power whenever it is active and only
releases it when runtime suspended.

This patch utilizes the new hdac_bus link_power op to plug
into HDA link state changes. By monitoring link state changes,
we can keep the controller side display power wakeref until
the codec driver has completed its work, and only release
the wakeref when codec driver is suspended.
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210205184630.1938761-4-kai.vehmanen@linux.intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>