net: dsa: sja1105: Add support for the PTP clock

The design of this PHC driver is influenced by the switch's behavior
w.r.t. timestamping.  It exposes two PTP counters, one free-running
(PTPTSCLK) and the other offset- and frequency-corrected in hardware
through PTPCLKVAL, PTPCLKADD and PTPCLKRATE.  The MACs can sample either
of these for frame timestamps.

However, the user manual warns that taking timestamps based on the
corrected clock is less than useful, as the switch can deliver corrupted
timestamps in a variety of circumstances.

Therefore, this PHC uses the free-running PTPTSCLK together with a
timecounter/cyclecounter structure that translates it into a software
time domain.  Thus, the settime/adjtime and adjfine callbacks are
hardware no-ops.

The timestamps (introduced in a further patch) will also be translated
to the correct time domain before being handed over to the userspace PTP
stack.

The introduction of a second set of PHC operations that operate on the
hardware PTPCLKVAL/PTPCLKADD/PTPCLKRATE in the future is somewhat
unavoidable, as the TTEthernet core uses the corrected PTP time domain.
However, the free-running counter + timecounter structure combination
will suffice for now, as the resulting timestamps yield a sub-50 ns
synchronization offset in steady state using linuxptp.

For this patch, in absence of frame timestamping, the operations of the
switch PHC were tested by syncing it to the system time as a local slave
clock with:

phc2sys -s CLOCK_REALTIME -c swp2 -O 0 -m -S 0.01

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 47 insertions, 0 deletions

diff --git a/drivers/net/dsa/sja1105/sja1105_ptp.h b/drivers/net/dsa/sja1105/sja1105_ptp.h
new file mode 100644
index 000000000000..137ffbb0a233
--- /dev/null
+++ b/drivers/net/dsa/sja1105/sja1105_ptp.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * Copyright (c) 2019, Vladimir Oltean <olteanv@gmail.com>
+ */
+#ifndef _SJA1105_PTP_H
+#define _SJA1105_PTP_H
+
+#if IS_ENABLED(CONFIG_NET_DSA_SJA1105_PTP)
+
+int sja1105_ptp_clock_register(struct sja1105_private *priv);
+
+void sja1105_ptp_clock_unregister(struct sja1105_private *priv);
+
+int sja1105et_ptp_cmd(const void *ctx, const void *data);
+
+int sja1105pqrs_ptp_cmd(const void *ctx, const void *data);
+
+int sja1105_get_ts_info(struct dsa_switch *ds, int port,
+			struct ethtool_ts_info *ts);
+
+int sja1105_ptp_reset(struct sja1105_private *priv);
+
+#else
+
+static inline int sja1105_ptp_clock_register(struct sja1105_private *priv)
+{
+	return 0;
+}
+
+static inline void sja1105_ptp_clock_unregister(struct sja1105_private *priv)
+{
+	return;
+}
+
+static inline int sja1105_ptp_reset(struct sja1105_private *priv)
+{
+	return 0;
+}
+
+#define sja1105et_ptp_cmd NULL
+
+#define sja1105pqrs_ptp_cmd NULL
+
+#define sja1105_get_ts_info NULL
+
+#endif /* IS_ENABLED(CONFIG_NET_DSA_SJA1105_PTP) */
+
+#endif /* _SJA1105_PTP_H */