[PATCH net v4 1/3] sfc: ptp: drop the stale frequency reset in efx_ptp_start()

[Alex Austin]

FW does not touch the clock frequency state on MC_CMD_PTP_OP_DISABLE or
MC_CMD_PTP_OP_ENABLE, so the driver doesn't need to either. Doing so
just desyncs the driver's cached current_adjfreq from what FW still has
programmed.

Resetting current_adjfreq to 0 here means the first efx_phc_adjtime()
call after efx_ptp_start() reprograms the NIC's clock frequency to 0,
since efx_phc_adjtime() always sends current_adjfreq to FW alongside
the time step. efx_ptp_start() runs on every SIOCSHWTSTAMP mode change,
on ifup, and on the reset_required path in efx_ptp_worker(), so each of
those silently drops any frequency correction the PTP servo had already
applied.

efx_ptp_start() is also reached from reset recovery, but that is fine:
on an FLR or PCIe reset FW does not touch the NIC clock, and on a full
MC reboot the clock is reset to 1970, so a stale current_adjfreq from
before the reset is hardly consequential - especially as it is bound to
MAX_PPB, 1000000 ppb.

Fixes: 7c236c43b838 ("sfc: Add support for IEEE-1588 PTP")

Signed-off-by: Alex Austin <alex.austin@xxxxxxx>
---
 drivers/net/ethernet/sfc/ptp.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/net/ethernet/sfc/ptp.c b/drivers/net/ethernet/sfc/ptp.c
index 6ca9a75..2247e5e 100644
--- a/drivers/net/ethernet/sfc/ptp.c
+++ b/drivers/net/ethernet/sfc/ptp.c
@@ -1446,7 +1446,6 @@ static int efx_ptp_start(struct efx_nic *efx)
 		goto fail;
 
 	ptp->evt_frag_idx = 0;
-	ptp->current_adjfreq = 0;
 
 	return 0;
 
-- 
2.34.1