[PATCH iwl-net v2 4/4] igc: Add lock preventing multiple simultaneous PTM transactions

[Chris H <christopher.s.hall@intel.com>]

From: Christopher S M Hall <christopher.s.hall@intel.com>

Add a mutex around the PTM transaction to prevent multiple transactors

Multiple processes try to initiate a PTM transaction, one or all may
fail. This can be reproduced by running two instances of the
following:

$ sudo phc2sys -O 0 -i tsn0 -m

PHC2SYS exits with:

"ioctl PTP_OFFSET_PRECISE: Connection timed out" when the PTM transaction
 fails

Note: Normally two instance of PHC2SYS will not run, but one process
 should not break another.

Fixes: a90ec8483732 ("igc: Add support for PTP getcrosststamp()")
Signed-off-by: Christopher S M Hall <christopher.s.hall@intel.com>
---
 drivers/net/ethernet/intel/igc/igc.h     |  1 +
 drivers/net/ethernet/intel/igc/igc_ptp.c | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
index eac0f966e0e4..323db1e2be38 100644
--- a/drivers/net/ethernet/intel/igc/igc.h
+++ b/drivers/net/ethernet/intel/igc/igc.h
@@ -319,6 +319,7 @@ struct igc_adapter {
 	struct timespec64 prev_ptp_time; /* Pre-reset PTP clock */
 	ktime_t ptp_reset_start; /* Reset time in clock mono */
 	struct system_time_snapshot snapshot;
+	struct mutex ptm_lock; /* Only allow one PTM transaction at a time */
 
 	char fw_version[32];
 
diff --git a/drivers/net/ethernet/intel/igc/igc_ptp.c b/drivers/net/ethernet/intel/igc/igc_ptp.c
index fb885fcaa97c..4e1379b7d2ee 100644
--- a/drivers/net/ethernet/intel/igc/igc_ptp.c
+++ b/drivers/net/ethernet/intel/igc/igc_ptp.c
@@ -1068,9 +1068,16 @@ static int igc_ptp_getcrosststamp(struct ptp_clock_info *ptp,
 {
 	struct igc_adapter *adapter = container_of(ptp, struct igc_adapter,
 						   ptp_caps);
+	int ret;
 
-	return get_device_system_crosststamp(igc_phc_get_syncdevicetime,
-					     adapter, &adapter->snapshot, cts);
+	/* This blocks until any in progress PTM transactions complete */
+	mutex_lock(&adapter->ptm_lock);
+
+	ret = get_device_system_crosststamp(igc_phc_get_syncdevicetime,
+					    adapter, &adapter->snapshot, cts);
+	mutex_unlock(&adapter->ptm_lock);
+
+	return ret;
 }
 
 static int igc_ptp_getcyclesx64(struct ptp_clock_info *ptp,
@@ -1169,6 +1176,7 @@ void igc_ptp_init(struct igc_adapter *adapter)
 	spin_lock_init(&adapter->ptp_tx_lock);
 	spin_lock_init(&adapter->free_timer_lock);
 	spin_lock_init(&adapter->tmreg_lock);
+	mutex_init(&adapter->ptm_lock);
 
 	adapter->tstamp_config.rx_filter = HWTSTAMP_FILTER_NONE;
 	adapter->tstamp_config.tx_type = HWTSTAMP_TX_OFF;
-- 
2.34.1