netdev - [PATCH net 3/3] can: ctucanfd: fix SSP_SRC in cases when bit-rate is higher than 1 MBit.

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Message-ID: <20260109135311.576033-4-mkl@pengutronix.de>
Date: Fri,  9 Jan 2026 14:46:12 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	kuba@...nel.org,
	linux-can@...r.kernel.org,
	kernel@...gutronix.de,
	Ondrej Ille <ondrej.ille@...il.com>,
	Pavel Pisa <pisa@....cvut.cz>,
	stable@...r.kernel.org,
	Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH net 3/3] can: ctucanfd: fix SSP_SRC in cases when bit-rate is higher than 1 MBit.

From: Ondrej Ille <ondrej.ille@...il.com>

The Secondary Sample Point Source field has been
set to an incorrect value by some mistake in the
past

  0b01 - SSP_SRC_NO_SSP - SSP is not used.

for data bitrates above 1 MBit/s. The correct/default
value already used for lower bitrates is

  0b00 - SSP_SRC_MEAS_N_OFFSET - SSP position = TRV_DELAY
         (Measured Transmitter delay) + SSP_OFFSET.

The related configuration register structure is described
in section 3.1.46 SSP_CFG of the CTU CAN FD
IP CORE Datasheet.

The analysis leading to the proper configuration
is described in section 2.8.3 Secondary sampling point
of the datasheet.

The change has been tested on AMD/Xilinx Zynq
with the next CTU CN FD IP core versions:

 - 2.6 aka master in the "integration with Zynq-7000 system" test
   6.12.43-rt12+ #1 SMP PREEMPT_RT kernel with CTU CAN FD git
   driver (change already included in the driver repo)
 - older 2.5 snapshot with mainline kernels with this patch
   applied locally in the multiple CAN latency tester nightly runs
   6.18.0-rc4-rt3-dut #1 SMP PREEMPT_RT
   6.19.0-rc3-dut

The logs, the datasheet and sources are available at

 https://canbus.pages.fel.cvut.cz/

Signed-off-by: Ondrej Ille <ondrej.ille@...il.com>
Signed-off-by: Pavel Pisa <pisa@....cvut.cz>
Link: https://patch.msgid.link/20260105111620.16580-1-pisa@fel.cvut.cz
Fixes: 2dcb8e8782d8 ("can: ctucanfd: add support for CTU CAN FD open-source IP core - bus independent part.")
Cc: stable@...r.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 drivers/net/can/ctucanfd/ctucanfd_base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/ctucanfd/ctucanfd_base.c b/drivers/net/can/ctucanfd/ctucanfd_base.c
index 1e6b9e3dc2fe..0ea1ff28dfce 100644
--- a/drivers/net/can/ctucanfd/ctucanfd_base.c
+++ b/drivers/net/can/ctucanfd/ctucanfd_base.c
@@ -310,7 +310,7 @@ static int ctucan_set_secondary_sample_point(struct net_device *ndev)
 		}
 
 		ssp_cfg = FIELD_PREP(REG_TRV_DELAY_SSP_OFFSET, ssp_offset);
-		ssp_cfg |= FIELD_PREP(REG_TRV_DELAY_SSP_SRC, 0x1);
+		ssp_cfg |= FIELD_PREP(REG_TRV_DELAY_SSP_SRC, 0x0);
 	}
 
 	ctucan_write32(priv, CTUCANFD_TRV_DELAY, ssp_cfg);
-- 
2.51.0