soundwire: stream: Poll for DP prepare to avoid interrupt deadlock

soundwire: stream: Poll for DP prepare to avoid interrupt deadlock

Replace the wait_for_completion_timeout() in sdw_prep_deprep_slave_ports()
with a read_poll_timeout().

The original intent of the wait_for_completion_timeout() was to wait for
the port prepare interrupt. But at this time the code is holding the
bus_lock, which prevents the interrupt handler from running. Because of
this, the port_prep completion will not be signaled and the
wait_for_completion_timeout() will always timeout.

Rewriting the code to avoid taking the bus_lock carries risks, and
needs careful consideration of the consequences. It is safer and simpler
to replace the completion with a simple register poll.

As the code is holding the bus_lock, it is already blocking other activity
so consuming control channel bandwidth for polling isn't really a concern.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20260227111648.175548-1-rf@opensource.cirrus.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>