[LTP] [PATCH v3 2/2] rtc02: skip (TCONF) on read-only RTCs that reject RTC_SET_TIME

[Kuba Pawlak]

Some RTC hardware does not allow setting the time from the host. For
example Qualcomm PMIC RTCs (rtc-pm8xxx) that are configured without the
allow-set-time DT property and without an nvmem/UEFI offset return
-ENODEV from RTC_SET_TIME; the counter free-runs from the epoch and is
only usable as an uptime source. On such devices rtc02 currently reports
TFAIL, which is a hardware limitation rather than a kernel defect.

Probe whether the RTC can be set in the setup phase, writing back the
value just read so a writable RTC is left unchanged. When RTC_SET_TIME
fails with ENODEV, skip the whole test with TCONF. Only ENODEV is treated
as "not supported": wider errnos such as EINVAL are used broadly by the
kernel and could mask a genuine failure, so anything else still results
in TBROK.

Doing the check in setup, before tst_rtc_clock_save(), also avoids the
cleanup path (tst_rtc_clock_restore()) issuing RTC_SET_TIME and turning
the run into a TBROK on such devices. If the probe succeeds the test body
runs as before, so no additional handling is needed there.

Signed-off-by: Kuba Pawlak <kuba.pawlak@canonical.com>
---
v3: drop the long explanatory comment; add a blank line between the
    RTC_RD_TIME and RTC_SET_TIME probes.

 testcases/kernel/device-drivers/rtc/rtc02.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/testcases/kernel/device-drivers/rtc/rtc02.c b/testcases/kernel/device-drivers/rtc/rtc02.c
index 34509ab..1b954f3 100644
--- a/testcases/kernel/device-drivers/rtc/rtc02.c
+++ b/testcases/kernel/device-drivers/rtc/rtc02.c
@@ -16,6 +16,7 @@
  */
 
 #include <stdio.h>
+#include <errno.h>
 #include "tst_rtctime.h"
 #include "tst_wallclock.h"
 #include "tst_test.h"
@@ -133,10 +134,20 @@ static void set_rtc_test(void)
 static void rtc_setup(void)
 {
 	int exists = access(rtc_dev, F_OK);
+	struct rtc_time probe_tm;
 
 	if (exists < 0)
 		tst_brk(TCONF, "RTC device %s not available", rtc_dev);
 
+	if (tst_rtc_gettime(rtc_dev, &probe_tm))
+		tst_brk(TBROK | TERRNO, "ioctl() RTC_RD_TIME");
+
+	if (tst_rtc_settime(rtc_dev, &probe_tm)) {
+		if (errno == ENODEV)
+			tst_brk(TCONF | TERRNO, "RTC does not support setting the time");
+		tst_brk(TBROK | TERRNO, "ioctl() RTC_SET_TIME");
+	}
+
 	tst_rtc_clock_save(rtc_dev);
 }
 
-- 
2.43.0