Add option to set maximum frequency adjustment.

The option sets an additional limit to the hardware limit. It's disabled
if set to zero. The default is 900000000 ppb.

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>

config.c

@@ -290,6 +290,11 @@ static enum parser_result parse_global_setting(const char *option,
 			return BAD_VALUE;
 		*cfg->pi_offset_const = df;
 
+	} else if (!strcmp(option, "pi_max_frequency")) {
+		if (1 != sscanf(value, "%d", &val) || !(val >= 0))
+			return BAD_VALUE;
+		*cfg->pi_max_frequency = val;
+
 	} else if (!strcmp(option, "ptp_dst_mac")) {
 		if (MAC_LEN != sscanf(value, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
 				      &mac[0], &mac[1], &mac[2], &mac[3], &mac[4], &mac[5]))

config.h

@@ -68,6 +68,7 @@ struct config {
 	double *pi_proportional_const;
 	double *pi_integral_const;
 	double *pi_offset_const;
+	int *pi_max_frequency;
 
 	unsigned char *ptp_dst_mac;
 	unsigned char *p2p_dst_mac;

default.cfg

@@ -41,6 +41,7 @@ kernel_leap		1
 pi_proportional_const	0.0
 pi_integral_const	0.0
 pi_offset_const         0.0
+pi_max_frequency	900000000
 clock_servo             pi
 #
 # Transport options

gPTP.cfg

@@ -40,6 +40,7 @@ kernel_leap		1
 pi_proportional_const	0.0
 pi_integral_const	0.0
 pi_offset_const         0.0
+pi_max_frequency	900000000
 clock_servo             pi
 #
 # Transport options

pi.c

@@ -31,10 +31,11 @@
 
 #define NSEC_PER_SEC 1000000000
 
-/* These two take their values from the configuration file. (see ptp4l.c) */
+/* These take their values from the configuration file. (see ptp4l.c) */
 double configured_pi_kp = 0.0;
 double configured_pi_ki = 0.0;
 double configured_pi_offset = 0.0;
+int configured_pi_max_freq = 900000000;
 
 struct pi_servo {
 	struct servo servo;
@@ -150,5 +151,9 @@ struct servo *pi_servo_create(int fadj, int max_ppb, int sw_ts)
 		s->max_offset = 0.0;
 	}
 
+	if (configured_pi_max_freq && s->maxppb > configured_pi_max_freq) {
+		s->maxppb = configured_pi_max_freq;
+	}
+
 	return &s->servo;
 }

pi.h

@@ -42,6 +42,12 @@ extern double configured_pi_ki;
  */
 extern double configured_pi_offset;
 
+/**
+ * When set to a non-zero value, this variable sets an additional limit for
+ * the frequency adjustment of the clock. It's in ppb.
+ */
+extern int configured_pi_max_freq;
+
 struct servo *pi_servo_create(int fadj, int max_ppb, int sw_ts);
 
 #endif

ptp4l.8

@@ -292,6 +292,12 @@ frequency instead of stepping the clock. When set to 0.0, the controller will
 never step the clock.
 The default is 0.0.
 .TP
+.B pi_max_frequency
+The maximum allowed frequency adjustment of the clock in parts per billion
+(ppb). This is an additional limit to the maximum allowed by the hardware. When
+set to 0, the hardware limit will be used.
+The default is 900000000 (90%).
+.TP
 .B ptp_dst_mac
 The MAC address where should be PTP messages sent.
 Relevant only with L2 transport. The default is 01:1B:19:00:00:00.

ptp4l.c

@@ -96,6 +96,7 @@ static struct config cfg_settings = {
 	.pi_proportional_const = &configured_pi_kp,
 	.pi_integral_const = &configured_pi_ki,
 	.pi_offset_const = &configured_pi_offset,
+	.pi_max_frequency = &configured_pi_max_freq,
 
 	.ptp_dst_mac = ptp_dst_mac,
 	.p2p_dst_mac = p2p_dst_mac,