[PATCH 6.1 218/232] net: sparx5/lan969x: fix PTP clock max_adj value

Sasha Levin
2026-02-28T18:14:33Z

From: Daniel Machon <daniel.machon@microchip.com>

[ Upstream commit a49d2a2c37a6252c41cbdd505f9d1c58d5a3817a ]

The max_adj field in ptp_clock_info tells userspace how much the PHC
clock frequency can be adjusted. ptp4l reads this and will never request
a correction larger than max_adj.

On both sparx5 and lan969x the clock offset may never converge because
the servo needs a frequency correction larger than the current max_adj
of 200000 (200 ppm) allows. The servo rails at the max and the offset
stays in the tens of microseconds.

The hardware has no inherent max adjustment limit; frequency correction
is done by writing a 64-bit clock period increment to CLK_PER_CFG, and
the register has plenty of range. The 200000 value was just an overly
conservative software limit. The max_adj is shared between sparx5 and
lan969x, and the increased value is safe for both.

Fix this by increasing max_adj to 10000000 (10000 ppm), giving the
servo sufficient headroom.

Fixes: 0933bd04047c ("net: sparx5: Add support for ptp clocks")
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260212-sparx5-ptp-max-adj-v2-v1-1-06b200e50ce3@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/microchip/sparx5/sparx5_ptp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/microchip/sparx5/sparx5_ptp.c b/drivers/net/ethernet/microchip/sparx5/sparx5_ptp.c
index 69e76634f9aa8..9c602f19d43b0 100644
--- a/drivers/net/ethernet/microchip/sparx5/sparx5_ptp.c
+++ b/drivers/net/ethernet/microchip/sparx5/sparx5_ptp.c
@@ -565,7 +565,7 @@ static int sparx5_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
static struct ptp_clock_info sparx5_ptp_clock_info = {
.owner = THIS_MODULE,
.name = "sparx5 ptp",
- .max_adj = 200000,
+ .max_adj = 10000000,
.gettime64 = sparx5_ptp_gettime64,
.settime64 = sparx5_ptp_settime64,
.adjtime = sparx5_ptp_adjtime,
--
2.51.0