[PATCH i-g-t] tests/kms_setmode: Check timing twice before asserting igt@kms_setmode@basic

[Jeevan B <jeevan.b@intel.com>]

The check_timings() function used to fail tests if vblank accuracy was slightly
off, which was too strict for High Refresh Rate (HRR) displays. HRR modes, are
more sensitive to small timing variations due to their shorter frame and
scanline times.

This change adjusts the accuracy check to allow retries and provides more
flexibility for minor timing differences, which is important for HRR tests.

Signed-off-by: Jeevan B <jeevan.b@intel.com>
---
 tests/kms_setmode.c | 42 ++++++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/tests/kms_setmode.c b/tests/kms_setmode.c
index 484c3a95f..f58f05ff1 100644
--- a/tests/kms_setmode.c
+++ b/tests/kms_setmode.c
@@ -461,7 +461,7 @@ static int test_stealing(int fd, struct crtc_config *crtc, uint32_t *ids)
 #define frame_time(km) (1000.0 * (km)->htotal * (km)->vtotal / (km)->clock)
 #define line_time(km) (1000.0 * (km)->htotal / (km)->clock)
 
-static void check_timings(int crtc_idx, const drmModeModeInfo *kmode)
+static bool check_timings(int crtc_idx, const drmModeModeInfo *kmode)
 {
 #define CALIBRATE_TS_STEPS 120 /* ~2s has to be less than 128! */
 	drmVBlank wait;
@@ -540,9 +540,12 @@ static void check_timings(int crtc_idx, const drmModeModeInfo *kmode)
 		 100 * accuracy / mean, accuracy / line_time(kmode));
 
 	/* 99.7% samples within one scanline on each side of mean */
-	igt_assert_f(accuracy < line_time(kmode),
-		     "vblank accuracy (%.3fus, %.1f%%) worse than a scanline (%.3fus)\n",
-		     accuracy, 100 * accuracy / mean, line_time(kmode));
+	if (accuracy >= line_time(kmode)) {
+		igt_info("vblank accuracy (%.3fus, %.1f%%) worse than a scanline (%.3fus)\n",
+			  accuracy, 100 * accuracy / mean, line_time(kmode));
+
+		return false;
+	}
 
 	/* At least 90% of frame times fall within the one scanline on each
 	 * side of expected mean.
@@ -565,12 +568,18 @@ static void check_timings(int crtc_idx, const drmModeModeInfo *kmode)
 	 * See:
 	 * https://en.wikipedia.org/wiki/Standard_deviation#Rules_for_normally_distributed_data
 	 */
-	igt_assert_f(fabs(mean - expected) < max(line_time(kmode), 1.718 * stddev),
-		     "vblank interval differs from modeline! expected %.1fus, measured %1.fus +- %.3fus, difference %.1fus (%.1f sigma, %.1f scanlines)\n",
-		     expected, mean, stddev,
-		     fabs(mean - expected),
-		     fabs(mean - expected) / stddev,
-		     fabs(mean - expected) / line_time(kmode));
+	if (fabs(mean - expected) >= max(line_time(kmode), 1.718 * stddev)) {
+		igt_info("vblank interval differs from modeline! expected %.1fus, "
+			 "measured %1.fus +- %.3fus, difference %.1fus (%.1f sigma, %.1f scanlines)\n",
+			  expected, mean, stddev,
+			  fabs(mean - expected),
+			  fabs(mean - expected) / stddev,
+			  fabs(mean - expected) / line_time(kmode));
+
+		return false;
+	}
+
+	return true;
 }
 
 static void test_crtc_config(const struct test_config *tconf,
@@ -654,8 +663,17 @@ retry:
 
 	igt_assert(config_failed == !!(tconf->flags & TEST_INVALID));
 
-	if (ret == 0 && tconf->flags & TEST_TIMINGS)
-		check_timings(crtcs[0].crtc_idx, &crtcs[0].mode);
+	if (ret == 0 && tconf->flags & TEST_TIMINGS) {
+		bool status = false;
+
+		for (int attempt = 1; attempt <= 2; attempt++) {
+			status = check_timings(crtcs[0].crtc_idx, &crtcs[0].mode);
+			if (status)
+				break;
+		}
+
+		igt_assert_f(status, "VBlank timing test failed after 2 attempt(s)\n");
+	}
 
 	return;
 }
-- 
2.25.1