drm/i915/selftests: Delay spinner before waiting for an interrupt

It seems that although (perhaps because of the memory stall?) the
spinner has signaled that it has started, it still takes some time to
spin up to 100% utilisation of the HW. Since the test depends on the
full utilisation of the HW to trigger the RPS interrupt, wait a little
bit and flush the interrupt status to be sure that the event we see if
from the spinner.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200417093928.17822-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/selftest_rps.c

@@ -14,6 +14,20 @@ static void dummy_rps_work(struct work_struct *wrk)
 {
 }
 
+static void sleep_for_ei(struct intel_rps *rps, int timeout_us)
+{
+	/* Flush any previous EI */
+	usleep_range(timeout_us, 2 * timeout_us);
+
+	/* Reset the interrupt status */
+	rps_disable_interrupts(rps);
+	GEM_BUG_ON(rps->pm_iir);
+	rps_enable_interrupts(rps);
+
+	/* And then wait for the timeout, for real this time */
+	usleep_range(2 * timeout_us, 3 * timeout_us);
+}
+
 static int __rps_up_interrupt(struct intel_rps *rps,
 			      struct intel_engine_cs *engine,
 			      struct igt_spinner *spin)
@@ -28,7 +42,6 @@ static int __rps_up_interrupt(struct intel_rps *rps,
 	intel_gt_pm_wait_for_idle(engine->gt);
 	GEM_BUG_ON(rps->active);
 
-	rps->pm_iir = 0;
 	rps->cur_freq = rps->min_freq;
 
 	rq = igt_spinner_create_request(spin, engine->kernel_context, MI_NOOP);
@@ -71,7 +84,7 @@ static int __rps_up_interrupt(struct intel_rps *rps,
 	timeout = intel_uncore_read(uncore, GEN6_RP_UP_EI);
 	timeout = GT_PM_INTERVAL_TO_US(engine->i915, timeout);
 
-	usleep_range(2 * timeout, 3 * timeout);
+	sleep_for_ei(rps, timeout);
 	GEM_BUG_ON(i915_request_completed(rq));
 
 	igt_spinner_end(spin);
@@ -122,16 +135,7 @@ static int __rps_down_interrupt(struct intel_rps *rps,
 	timeout = intel_uncore_read(uncore, GEN6_RP_DOWN_EI);
 	timeout = GT_PM_INTERVAL_TO_US(engine->i915, timeout);
 
-	/* Flush any previous EI */
-	usleep_range(timeout, 2 * timeout);
-
-	/* Reset the interrupt status */
-	rps_disable_interrupts(rps);
-	GEM_BUG_ON(rps->pm_iir);
-	rps_enable_interrupts(rps);
-
-	/* And then wait for the timeout, for real this time */
-	usleep_range(2 * timeout, 3 * timeout);
+	sleep_for_ei(rps, timeout);
 
 	if (rps->cur_freq != rps->max_freq) {
 		pr_err("%s: Frequency unexpectedly changed [down], now %d!\n",