[PATCH net-next 4/5] ice: trigger PFINT_OICR_TSYN_TX interrupt instead of polling

[Tony Nguyen <anthony.l.nguyen@intel.com>]

From: Jacob Keller <jacob.e.keller@intel.com>

In ice_misc_intr_thread_fn(), if we do not complete all Tx timestamp work,
the thread function will poll continuously forever.

For E822 hardware, this wastes time as the return value from
ice_ptp_process_ts() is accurate and always reports correctly that the PHY
actually has new timestamp data.

In addition, if we receive enough timestamps with the right pacing, we may
never exit this polling. Should this occur, other tasks handled by the
ice_misc_intr_thread_fn() will never be processed.

Fix this by instead writing to PFINT_OICR, causing an emulated interrupt to
be triggered immediately. This does take slightly more processing than just
re-checking the timestamps. However, it allows all of the other interrupt
causes a chance to be processed first in the hard IRQ function.

Note that the OICR interrupt is configured to be throttled  to no more than
once every 124 microseconds. This gives an effective interrupt rate of
~8000 interrupts per second. This should thus not cause a significant
increase in overall CPU usage when compared to sleeping.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Arpana Arland <arpanax.arland@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/ice/ice_main.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
index 6811e2a3c154..2665f72b5461 100644
--- a/drivers/net/ethernet/intel/ice/ice_main.c
+++ b/drivers/net/ethernet/intel/ice/ice_main.c
@@ -3202,8 +3202,15 @@ static irqreturn_t ice_misc_intr_thread_fn(int __always_unused irq, void *data)
 		ice_ptp_extts_event(pf);
 
 	if (test_and_clear_bit(ICE_MISC_THREAD_TX_TSTAMP, pf->misc_thread)) {
-		while (ice_ptp_process_ts(pf) == ICE_TX_TSTAMP_WORK_PENDING)
-			usleep_range(50, 100);
+		struct ice_hw *hw = &pf->hw;
+
+		/* Process outstanding Tx timestamps. If there is more work,
+		 * re-arm the interrupt to trigger again.
+		 */
+		if (ice_ptp_process_ts(pf) == ICE_TX_TSTAMP_WORK_PENDING) {
+			wr32(hw, PFINT_OICR, PFINT_OICR_TSYN_TX_M);
+			ice_flush(hw);
+		}
 	}
 
 	return IRQ_HANDLED;
-- 
2.38.1