[PATCH] amd-xgbe: fix PTP addend overflow causing frozen clock

[Gregory Fuchedgi via B4 Relay <devnull+gfuchedgi.gmail.com@kernel.org>]

From: Gregory Fuchedgi <gfuchedgi@gmail.com>

XGBE_PTP_ACT_CLK_FREQ and XGBE_V2_PTP_ACT_CLK_FREQ were 10x too
large (500MHz/1GHz instead of 50MHz/100MHz), causing the computed
addend to overflow the 32-bit tstamp_addend. In the general case
this would result in the clock advancing at the wrong rate. For v2
(PCI), ptpclk_rate is hardcoded to 125MHz, so the addend formula
(ACT_CLK_FREQ << 32) / ptpclk_rate yields exactly 8 * 2^32, and
when stored to the 32-bit tstamp_addend the value is zero. With
addend = 0 the hardware accumulator never overflows and the PTP
clock is fully stopped. For v1 (platform), ptpclk_rate is read from
ACPI/DT so the exact overflow behavior depends on the
firmware-reported frequency.

Define the constants as NSEC_PER_SEC / SSINC so the relationship is
explicit and cannot drift out of sync.

Fixes: fbd47be098b5 ("amd-xgbe: add hardware PTP timestamping support")
Tested-by: Gregory Fuchedgi <gfuchedgi@gmail.com>
Signed-off-by: Gregory Fuchedgi <gfuchedgi@gmail.com>
---
Tested by running ptp4l and verifying successful clock synchronization on v2
(PCI) hardware.
---
 drivers/net/ethernet/amd/xgbe/xgbe.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe.h b/drivers/net/ethernet/amd/xgbe/xgbe.h
index 60b7e53206d1..3d3b09010d48 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe.h
+++ b/drivers/net/ethernet/amd/xgbe/xgbe.h
@@ -135,11 +135,11 @@
  */
 #define XGBE_TSTAMP_SSINC	20
 #define XGBE_TSTAMP_SNSINC	0
-#define XGBE_PTP_ACT_CLK_FREQ	500000000
+#define XGBE_PTP_ACT_CLK_FREQ	(NSEC_PER_SEC / XGBE_TSTAMP_SSINC)
 
 #define XGBE_V2_TSTAMP_SSINC	0xA
 #define XGBE_V2_TSTAMP_SNSINC	0
-#define XGBE_V2_PTP_ACT_CLK_FREQ	1000000000
+#define XGBE_V2_PTP_ACT_CLK_FREQ	(NSEC_PER_SEC / XGBE_V2_TSTAMP_SSINC)
 
 /* Define maximum supported values */
 #define XGBE_MAX_PPS_OUT	4

---
base-commit: 0c7a5ba011d336df4fcd1f667fcc16ea5549be12
change-id: 20260428-fix-xgbe-ptp-addend-ccb1df627622

Best regards,
-- 
Gregory Fuchedgi <gfuchedgi@gmail.com>