ntp: allow TX-only HW timestamping by default

If no rxfilter is specified in the hwtimestamp directive and the NIC
doesn't support the all or ntp filter, enable TX-only HW timestamping
with the none filter.

conf.c

@@ -1281,7 +1281,7 @@ parse_hwtimestamp(char *line)
   iface->name = Strdup(p);
   iface->minpoll = 0;
   iface->nocrossts = 0;
-  iface->rxfilter = CNF_HWTS_RXFILTER_NTP;
+  iface->rxfilter = CNF_HWTS_RXFILTER_ANY;
   iface->precision = 100.0e-9;
   iface->tx_comp = 0.0;
   iface->rx_comp = 0.0;

conf.h

@@ -118,9 +118,10 @@ extern char *CNF_GetHwclockFile(void);
 extern int CNF_GetInitSources(void);
 extern double CNF_GetInitStepThreshold(void);
 
-#define CNF_HWTS_RXFILTER_NONE 0
+#define CNF_HWTS_RXFILTER_ANY 0
-#define CNF_HWTS_RXFILTER_NTP 1
+#define CNF_HWTS_RXFILTER_NONE 1
-#define CNF_HWTS_RXFILTER_ALL 2
+#define CNF_HWTS_RXFILTER_NTP 2
+#define CNF_HWTS_RXFILTER_ALL 3
 
 typedef struct {
   char *name;

doc/chrony.conf.adoc

@@ -1886,11 +1886,12 @@ be enabled by the *xleave* option in the <<server,*server*>> or the
 This directive is supported on Linux 3.19 and newer. The NIC must support HW
 timestamping, which can be verified with the *ethtool -T* command. The list of
 capabilities should include _SOF_TIMESTAMPING_RAW_HARDWARE_,
-_SOF_TIMESTAMPING_TX_HARDWARE_, _SOF_TIMESTAMPING_RX_HARDWARE_, and the receive
+_SOF_TIMESTAMPING_TX_HARDWARE_, and _SOF_TIMESTAMPING_RX_HARDWARE_. Receive
-filters should include _HWTSTAMP_FILTER_ALL_ or _HWTSTAMP_FILTER_NTP_ALL_. When
+filter _HWTSTAMP_FILTER_ALL_, or _HWTSTAMP_FILTER_NTP_ALL_, is necessary for
-*chronyd* is running, no other process (e.g. a PTP daemon) should be working
+timestamping of received packets. Timestamping of packets received from bridged
-with the NIC clock. HW timestamping of packets received from bridged and bonded
+and bonded interfaces is supported on Linux 4.13 and newer. When *chronyd* is
-interfaces is supported on Linux 4.13 and newer.
+running, no other process (e.g. a PTP daemon) should be working with the NIC
+clock.
 +
 If the kernel supports software timestamping, it will be enabled for all
 interfaces. The source of timestamps (i.e. hardware, kernel, or daemon) is
@@ -1925,15 +1926,21 @@ is 0.
 Some hardware can precisely cross timestamp the NIC clock with the system
 clock. This option disables the use of the cross timestamping.
 *rxfilter* _filter_:::
-This option selects the receive timestamping filter. Possible values are:
+This option selects the receive timestamping filter. The _filter_ can be one of
-_all_, _ntp_, and _none_. The default value is _ntp_, which enables
+the following:
-timestamping of NTP packets (_HWTSTAMP_FILTER_NTP_ALL_) if it is supported, or
+_all_::::
-timestamping of all packets (_HWTSTAMP_FILTER_ALL_). Setting *rxfilter* to
+Enables timestamping of all received packets.
-_all_ forces timestamping of all packets, which can be useful when the NIC
+_ntp_::::
-supports both filters and NTP packets are received from or on a non-standard
+Enables timestamping of received NTP packets.
-UDP port (e.g. specified by the *port* directive). Setting *rxfilter* to _none_
+_none_::::
-disables receive HW timestamping and allows transmit HW timestamping to be
+Disables timestamping of received packets.
-enabled when the NIC supports only PTP-specific receive filters.
+:::
+The most specific filter for timestamping NTP packets which is supported by the
+NIC is selected by default. Some NICs can timestamp only PTP packets, which
+limits the selection to the _none_ filter. Forcing timestamping of all packets
+with the _all_ filter when the NIC supports both _all_ and _ntp_ filters can be
+useful when packets are received from or on a non-standard UDP port (e.g.
+specified by the *port* directive).
 ::
 +
 Examples of the directive are:

ntp_io_linux.c

@@ -154,17 +154,25 @@ add_interface(CNF_HwTsInterface *conf_iface)
   ts_config.tx_type = HWTSTAMP_TX_ON;
 
   switch (conf_iface->rxfilter) {
+    case CNF_HWTS_RXFILTER_ANY:
+#ifdef HAVE_LINUX_TIMESTAMPING_RXFILTER_NTP
+      if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_NTP_ALL))
+        ts_config.rx_filter = HWTSTAMP_FILTER_NTP_ALL;
+      else
+#endif
+      if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_ALL))
+        ts_config.rx_filter = HWTSTAMP_FILTER_ALL;
+      else
+        ts_config.rx_filter = HWTSTAMP_FILTER_NONE;
+      break;
     case CNF_HWTS_RXFILTER_NONE:
       ts_config.rx_filter = HWTSTAMP_FILTER_NONE;
       break;
-    case CNF_HWTS_RXFILTER_NTP:
 #ifdef HAVE_LINUX_TIMESTAMPING_RXFILTER_NTP
-      if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_NTP_ALL)) {
+    case CNF_HWTS_RXFILTER_NTP:
-        ts_config.rx_filter = HWTSTAMP_FILTER_NTP_ALL;
+      ts_config.rx_filter = HWTSTAMP_FILTER_NTP_ALL;
-        break;
+      break;
-      }
 #endif
-      /* Fall through */
     default:
       ts_config.rx_filter = HWTSTAMP_FILTER_ALL;
       break;
@@ -203,7 +211,8 @@ add_interface(CNF_HwTsInterface *conf_iface)
 
   iface->clock = HCL_CreateInstance(UTI_Log2ToDouble(MAX(conf_iface->minpoll, MIN_PHC_POLL)));
 
-  LOG(LOGS_INFO, "Enabled HW timestamping on %s", iface->name);
+  LOG(LOGS_INFO, "Enabled HW timestamping %son %s",
+      ts_config.rx_filter == HWTSTAMP_FILTER_NONE ? "(TX only) " : "", iface->name);
 
   return 1;
 }