usb: cdnsp: Fix issue with detecting command completion event

usb: cdnsp: Fix issue with detecting command completion event

In some cases, there is a small-time gap in which CMD_RING_BUSY can be
cleared by controller but adding command completion event to event ring
will be delayed. As the result driver will return error code.

This behavior has been detected on usbtest driver (test 9) with
configuration including ep1in/ep1out bulk and ep2in/ep2out isoc
endpoint.

Probably this gap occurred because controller was busy with adding some
other events to event ring.

The CMD_RING_BUSY is cleared to '0' when the Command Descriptor has been
executed and not when command completion event has been added to event
ring.

To fix this issue for this test the small delay is sufficient less than
10us) but to make sure the problem doesn't happen again in the future
the patch introduces 10 retries to check with delay about 20us before
returning error code.

Fixes: 3d82904559f4 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
Cc: stable <stable@kernel.org>
Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Acked-by: Peter Chen <peter.chen@kernel.org>
Link: https://lore.kernel.org/r/PH7PR07MB9538AA45362ACCF1B94EE9B7DD96A@PH7PR07MB9538.namprd07.prod.outlook.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>