[PATCH 2/2] gpu: host1x: skip redundant HW state update

[Tanmay Patil <tanmayp@nvidia.com>]

When the fence list is empty, host1x_intr_update_hw_state()
falls through to host1x_intr_disable_syncpt_intr()
which does two MMIO writes to disable the syncpoint
interrupt and clear its status.

The ISR has already disabled and acked the interrupt
before calling host1x_intr_handle_interrupt(), making
these two writes redundant. Skip the update_hw_state()
call if no fences remain.

Measured Syncpoint wait latency (50000 samples):
  Average latency:   10.6 us  -> 9.4 us
  99.99 pct latency: 51.90 us -> 36.58 us

Signed-off-by: Tanmay Patil <tanmayp@nvidia.com>
---
 drivers/gpu/host1x/intr.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/host1x/intr.c b/drivers/gpu/host1x/intr.c
index f77a678949e9..723297250768 100644
--- a/drivers/gpu/host1x/intr.c
+++ b/drivers/gpu/host1x/intr.c
@@ -92,8 +92,12 @@ void host1x_intr_handle_interrupt(struct host1x *host, unsigned int id)
 		host1x_fence_signal(fence);
 	}
 
-	/* Re-enable interrupt if necessary */
-	host1x_intr_update_hw_state(host, sp);
+	/*
+	 * Re-enable interrupt if necessary. The ISR already disabled the interrupt,
+	 * so if no fences remain, no update is needed.
+	 */
+	if (!list_empty(&sp->fences.list))
+		host1x_intr_update_hw_state(host, sp);
 
 	spin_unlock(&sp->fences.lock);
 }
-- 
2.54.0