From 5b8fa684ae632bf128e2798aa9ac140e9e4c81f0 Mon Sep 17 00:00:00 2001
From: Richard Cochran <richardcochran@gmail.com>
Date: Sat, 12 Nov 2011 18:18:44 +0100
Subject: [PATCH] phc: Add a method to query the maximum adjustment.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
---
 phc.c | 17 +++++++++++++++++
 phc.h |  9 +++++++++
 2 files changed, 26 insertions(+)

diff --git a/phc.c b/phc.c
index d733cb2..16a61ef 100644
--- a/phc.c
+++ b/phc.c
@@ -16,11 +16,15 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
+#include <stdio.h>
+#include <sys/ioctl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
 
+#include <linux/ptp_clock.h>
+
 #include "phc.h"
 
 clockid_t phc_open(char *phc)
@@ -37,3 +41,16 @@ void phc_close(clockid_t clkid)
 
 	close(CLOCKID_TO_FD(clkid));
 }
+
+int phc_max_adj(clockid_t clkid)
+{
+	int fd = CLOCKID_TO_FD(clkid);
+	struct ptp_clock_caps caps;
+
+	if (ioctl(fd, PTP_CLOCK_GETCAPS, &caps)) {
+		perror("PTP_CLOCK_GETCAPS");
+		return 0;
+	}
+
+	return caps.max_adj;
+}
diff --git a/phc.h b/phc.h
index 8ea9e05..5eb775d 100644
--- a/phc.h
+++ b/phc.h
@@ -37,4 +37,13 @@ clockid_t phc_open(char *phc);
  */
 void phc_close(clockid_t clkid);
 
+/**
+ * Query the maximum frequency adjustment of a PTP hardware clock device.
+ *
+ * @param clkid A clock ID obtained using phc_open().
+ *
+ * @return The clock's maximum frequency adjustment in parts per billion.
+ */
+int phc_max_adj(clockid_t clkid);
+
 #endif