ice: add lock to protect low latency interface

ice: add lock to protect low latency interface

Newer firmware for the E810 devices support a 'low latency' interface to
interact with the PHY without using the Admin Queue. This is interacted
with via the REG_LL_PROXY_L and REG_LL_PROXY_H registers.

Currently, this interface is only used for Tx timestamps. There are two
different mechanisms, including one which uses an interrupt for firmware to
signal completion. However, these two methods are mutually exclusive, so no
synchronization between them was necessary.

This low latency interface is being extended in future firmware to support
also programming the PHY timers. Use of the interface for PHY timers will
need synchronization to ensure there is no overlap with a Tx timestamp.

The interrupt-based response complicates the locking somewhat. We can't use
a simple spinlock. This would require being acquired in
ice_ptp_req_tx_single_tstamp, and released in
ice_ptp_complete_tx_single_tstamp. The ice_ptp_req_tx_single_tstamp
function is called from the threaded IRQ, and the
ice_ptp_complete_tx_single_stamp is called from the low latency IRQ, so we
would need to acquire the lock with IRQs disabled.

To handle this, we'll use a wait queue along with
wait_event_interruptible_locked_irq in the update flows which don't use the
interrupt.

The interrupt flow will acquire the wait queue lock, set the
ATQBAL_FLAGS_INTR_IN_PROGRESS, and then initiate the firmware low latency
request, and unlock the wait queue lock.

Upon receipt of the low latency interrupt, the lock will be acquired, the
ATQBAL_FLAGS_INTR_IN_PROGRESS bit will be cleared, and the firmware
response will be captured, and wake_up_locked() will be called on the wait
queue.

The other flows will use wait_event_interruptible_locked_irq() to wait
until the ATQBAL_FLAGS_INTR_IN_PROGRESS is clear. This function checks the
condition under lock, but does not hold the lock while waiting. On return,
the lock is held, and a return of zero indicates we hold the lock and the
in-progress flag is not set.

This will ensure that threads which need to use the low latency interface
will sleep until they can acquire the lock without any pending low latency
interrupt flow interfering.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Milena Olech <milena.olech@intel.com>
Signed-off-by: Anton Nadezhdin <anton.nadezhdin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>