To initialize the taprio block in lan966x, it is required to configure
the register REVISIT_DLY. The purpose of this register is to set the
delay before revisit the next gate and the value of this register depends
on the system clock. The problem is that the we calculated wrong the value
of the system clock period in picoseconds. The actual system clock is
~165.617754MHZ and this correspond to a period of 6038 pico seconds and
not 15125 as currently set.

Fixes: e462b2717380b4 ("net: lan966x: Add offload support for taprio")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>

---
v2-v3:
- start to use the define

v1->v2:
- add define for system clock and calculate the period in picoseconds
---
 drivers/net/ethernet/microchip/lan966x/lan966x_ptp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_ptp.c b/drivers/net/ethernet/microchip/lan966x/lan966x_ptp.c
index b4377b8613c3a..8c40db90ee8f6 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_ptp.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_ptp.c
@@ -1,11 +1,14 @@
 // SPDX-License-Identifier: GPL-2.0+
 
 #include <linux/ptp_classify.h>
+#include <linux/units.h>
 
 #include "lan966x_main.h"
 #include "vcap_api.h"
 #include "vcap_api_client.h"
 
+#define LAN9X66_CLOCK_RATE	165617754
+
 #define LAN966X_MAX_PTP_ID	512
 
 /* Represents 1ppm adjustment in 2^59 format with 6.037735849ns as reference
@@ -1126,5 +1129,5 @@ void lan966x_ptp_rxtstamp(struct lan966x *lan966x, struct sk_buff *skb,
 u32 lan966x_ptp_get_period_ps(void)
 {
 	/* This represents the system clock period in picoseconds */
-	return 15125;
+	return PICO / LAN9X66_CLOCK_RATE;
 }
-- 
2.34.1

On Fri, Nov 21, 2025 at 07:14:11AM +0100, Horatiu Vultur wrote:
> To initialize the taprio block in lan966x, it is required to configure
> the register REVISIT_DLY. The purpose of this register is to set the
> delay before revisit the next gate and the value of this register depends
> on the system clock. The problem is that the we calculated wrong the value
> of the system clock period in picoseconds. The actual system clock is
> ~165.617754MHZ and this correspond to a period of 6038 pico seconds and
> not 15125 as currently set.
> 
> Fixes: e462b2717380b4 ("net: lan966x: Add offload support for taprio")
> Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
> 
> ---
> v2-v3:
> - start to use the define
> 
> v1->v2:
> - add define for system clock and calculate the period in picoseconds

Thanks, I agree with this analysis.
And believe v3 addresses the review of earlier versions.

Reviewed-by: Simon Horman <horms@kernel.org>