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

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

[Daniel Machon]

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>
---
 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 2f168700f63c..8b2e07821a95 100644
--- a/drivers/net/ethernet/microchip/sparx5/sparx5_ptp.c
+++ b/drivers/net/ethernet/microchip/sparx5/sparx5_ptp.c
@@ -576,7 +576,7 @@ 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,

---
base-commit: 83310d613382f74070fc8b402f3f6c2af8439ead
change-id: 20260211-sparx5-ptp-max-adj-v2-54ceb8ad6baa

Best regards,
-- 
Daniel Machon <daniel.machon@microchip.com>

Re: [PATCH net] net: sparx5/lan969x: fix PTP clock max_adj value

[Maxime Chevallier]

Hi Daniel,

On 12/02/2026 12:02, Daniel Machon wrote:
> 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.

That's arbitrary, but looks like there's plenty of other drivers that do
similar things :)

> 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>

Maxime

Re: [PATCH net] net: sparx5/lan969x: fix PTP clock max_adj value

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 12 Feb 2026 12:02:30 +0100 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [net] net: sparx5/lan969x: fix PTP clock max_adj value
    https://git.kernel.org/netdev/net/c/a49d2a2c37a6

You are awesome, thank you!
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