ptp4l: Allow advertisement of legacy PTP 2.0 protocol

Some hardware can't properly timestamp packets with the new PTP
header version 2.1. This patch adds legacy_ptp_ver config option that
allows advertising of the legacy 2.0 protocol.

Additionally, forcing PTP minor version to be nonzero causes
interoperability issues with some legacy grandmasters.

v2: rebase on top, clarify compatibility issues
v3: fix subject line
v4: change argument to ptp_minor_version

Signed-off-by: Maciek Machnikowski <[email protected]>

Author: MaciekMachni

config.c

@@ -318,6 +318,7 @@ struct config_item config_tab[] = {
 	GLOB_ITEM_STR("productDescription", ";;"),
 	PORT_ITEM_STR("ptp_dst_mac", "01:1B:19:00:00:00"),
 	PORT_ITEM_STR("p2p_dst_mac", "01:80:C2:00:00:0E"),
+	GLOB_ITEM_INT("ptp_minor_version", 1, 0, 1),
 	GLOB_ITEM_STR("refclock_sock_address", "/var/run/refclock.ptp.sock"),
 	GLOB_ITEM_STR("revisionData", ";;"),
 	GLOB_ITEM_INT("sanity_freq_limit", 200000000, 0, INT_MAX),

configs/default.cfg

@@ -46,6 +46,7 @@ power_profile.2011.networkTimeInaccuracy	-1
 power_profile.2017.totalTimeInaccuracy		-1
 power_profile.grandmasterID			0
 power_profile.version				none
+ptp_minor_version       1
 #
 # Run time options
 #

ptp4l.8

@@ -810,6 +810,11 @@ selection algorithm, lower values take precedence. Must be in the range 0 to
 255.
 The default is 128.
 
+.TP
+.B ptp_minor_version
+This option sets the minorVersionPTP in the common PTP message header.
+The default is 1.
+
 .TP
 .B refclock_sock_address
 The address of the UNIX domain socket to be used by the refclock_sock servo.

ptp4l.c

@@ -192,6 +192,9 @@ int main(int argc, char *argv[])
 	sk_tx_timeout = config_get_int(cfg, NULL, "tx_timestamp_timeout");
 	sk_hwts_filter_mode = config_get_int(cfg, NULL, "hwts_filter");
 
+	ptp_hdr_ver = config_get_int(cfg, NULL, "ptp_minor_version");
+	ptp_hdr_ver = (ptp_hdr_ver << 4) | PTP_MAJOR_VERSION;
+
 	if (config_get_int(cfg, NULL, "clock_servo") == CLOCK_SERVO_NTPSHM) {
 		config_set_int(cfg, "kernel_leap", 0);
 		config_set_int(cfg, "sanity_freq_limit", 0);