linux-kernel - [PATCH 2/2] Documentation, update rtctest.c to verify passage of time

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Date:	Mon, 16 Mar 2015 11:58:55 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	corbet@....net, rtc-linux@...glegroups.com,
	linux-doc@...r.kernel.org, a.zummo@...ertech.it,
	Prarit Bhargava <prarit@...hat.com>
Subject: [PATCH 2/2] Documentation, update rtctest.c to verify passage of time

rtctest.c checks to see if PIE is functioning by testing if 20 interrupts occur
at rates from 2HZ to 64HZ.  While this check is good, it does not check to
see if the correct amount of time has actually passed.  This misses
situations where the RTC may be operating at a higher or lower frequency
than expected.

This patch introduces a simple check to verify if the time passed is
less than 10% of what was programmed into the RTC.

Also make a simple one line change to rtc.txt to point to the right test
program.

Signed-off-by: Prarit Bhargava <prarit@...hat.com>
---
 Documentation/rtc/rtc.txt   |    2 +-
 Documentation/rtc/rtctest.c |   13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/rtc/rtc.txt b/Documentation/rtc/rtc.txt
index fd6e0cd..7f05eb7 100644
--- a/Documentation/rtc/rtc.txt
+++ b/Documentation/rtc/rtc.txt
@@ -204,4 +204,4 @@ Some common examples:
 
     *	RTC_PIE_ON, RTC_PIE_OFF: These are also emulated by the generic code.
 
-If all else fails, check out the rtc-test.c driver!
+If all else fails, check out the Documentation/rtc/rtctest.c driver!
diff --git a/Documentation/rtc/rtctest.c b/Documentation/rtc/rtctest.c
index 1e06f46..d80ae85 100644
--- a/Documentation/rtc/rtctest.c
+++ b/Documentation/rtc/rtctest.c
@@ -36,6 +36,7 @@ int main(int argc, char **argv)
 	unsigned long tmp, data;
 	struct rtc_time rtc_tm;
 	const char *rtc = default_rtc;
+	struct timeval start, end, diff;
 
 	switch (argc) {
 	case 2:
@@ -230,12 +231,24 @@ test_PIE:
 		}
 
 		for (i=1; i<21; i++) {
+			gettimeofday(&start, NULL);
 			/* This blocks */
 			retval = read(fd, &data, sizeof(unsigned long));
 			if (retval == -1) {
 				perror("read");
 				exit(errno);
 			}
+			gettimeofday(&end, NULL);
+			timersub(&end, &start, &diff);
+			if (diff.tv_sec > 0 ||
+			    diff.tv_usec > ((1000000L / tmp) * 1.10)) {
+				fprintf(stderr, "\nPIE delta error: %ld.%06ld should be close to 0.%06ld\n",
+				       diff.tv_sec, diff.tv_usec,
+				       (1000000L / tmp));
+				fflush(stdout);
+				exit(-1);
+			}
+
 			fprintf(stderr, " %d",i);
 			fflush(stderr);
 			irqcount++;
-- 
1.7.9.3

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