selftest: rtc: Check if could access /dev/rtc0 before testing

The rtctest requires the read permission on /dev/rtc0. The rtctest will
be skipped if the /dev/rtc0 is not readable.
Reviewed-by: Koba Ko <kobak@nvidia.com>
Reviewed-by: Matthew R. Ochs <mochs@nvidia.com>
Signed-off-by: Joseph Jang <jjang@nvidia.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/rtc/rtctest.c

@@ -412,6 +412,8 @@ TEST_F_TIMEOUT(rtc, alarm_wkalm_set_minute, 65) {
 
 int main(int argc, char **argv)
 {
+	int ret = -1;
+
 	switch (argc) {
 	case 2:
 		rtc_file = argv[1];
@@ -423,5 +425,12 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	return test_harness_run(argc, argv);
+	/* Run the test if rtc_file is accessible */
+	if (access(rtc_file, R_OK) == 0)
+		ret = test_harness_run(argc, argv);
+	else
+		ksft_exit_skip("[SKIP]: Cannot access rtc file %s - Exiting\n",
+						rtc_file);
+
+	return ret;
 }