soundwire: intel: conditionally exit clock stop mode on system suspend

soundwire: intel: conditionally exit clock stop mode on system suspend

Intel stress tests reported issues with the clock stop mode,
specifically when trying to do a system suspend while the link is
already pm_runtime suspended.

In this case, we need to disable the shim wake, but when the PCI
parent device is also pm_runtime suspended the SHIM registers are not
accessible.

Since this is an invalid corner case, this patch suggests a pm_runtime
resume of the entire bus to full power (parent+child devices) before
the system suspend so that the shim wake can be disabled.

Unlike the suspend operation, the .prepare callbacks are propagated
from root device to leaf devices. By adding a .prepare callback at the
SoundWire link level, we can double-check the pm_runtime status of the
device as well as its parent PCI device. When the problematic
configuration is detected, the device is pm_runtime resumed - which by
construction also resume its parent.

An additional loop is added to resume all child devices. In theory we
only need to restart the link, but doing so will also cause the
physical devices to synchronize and re-initialize, while their Linux
devices remain pm_runtime suspended. It's simpler to make sure the
codec devices are fully resumed so that we don't have to deal with
zombie states.

This additional loop could have been avoided by adding a .prepare
callback in SoundWire codec drivers. Functionally this would have been
equivalent. The rationale for implementing a loop at the link level is
only to reduce the amount of code required to deal at the codec level
with an Intel corner case - in other words keep codec drivers
independent from Intel platform-specific programming sequences.

BugLink: https://github.com/thesofproject/linux/issues/2606
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20210818024954.16873-4-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>