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

[Jeevan B]

The check_timings() function previously failed tests if vblank timing was
slightly off. This was too strict in general and caused false failures due
to small timing variations, especially on some displays.

This change adjusts the accuracy check to allow retries and provides more
flexibility for minor timing differences.

v2: Fix commit message and add igt_info for retry.

Signed-off-by: Jeevan B <jeevan.b at intel.com>
---
 tests/kms_setmode.c | 43 +++++++++++++++++++++++++++++++------------
 1 file changed, 31 insertions(+), 12 deletions(-)

diff --git a/tests/kms_setmode.c b/tests/kms_setmode.c
index 484c3a95f..753c65ec0 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 +663,18 @@ 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_info("Timing check failed on attempt %d, retrying...\n", attempt);
+		}
+
+		igt_assert_f(status, "VBlank timing test failed after 2 attempt(s)\n");
+	}
 
 	return;
 }
-- 
2.25.1