6.1-stable review patch. If anyone has any objections, please let me know.
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From: Kelsey Maes kelsey@vpprocess.com
[ Upstream commit 5e1663810e11c64956aa7e280cf74b2f3284d816 ]
The TDC is currently hardcoded enabled. This means that even for lower CAN-FD data bitrates (with a DBRP (data bitrate prescaler) > 2) a TDC is configured. This leads to a bus-off condition.
ISO 11898-1 section 11.3.3 says "Transmitter delay compensation" (TDC) is only applicable if DBRP is 1 or 2.
To fix the problem, switch the driver to use the TDC calculation provided by the CAN driver framework (which respects ISO 11898-1 section 11.3.3). This has the positive side effect that userspace can control TDC as needed.
Demonstration of the feature in action: | $ ip link set can0 up type can bitrate 125000 dbitrate 500000 fd on | $ ip -details link show can0 | 3: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10 | link/can promiscuity 0 allmulti 0 minmtu 0 maxmtu 0 | can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0 | bitrate 125000 sample-point 0.875 | tq 50 prop-seg 69 phase-seg1 70 phase-seg2 20 sjw 10 brp 2 | mcp251xfd: tseg1 2..256 tseg2 1..128 sjw 1..128 brp 1..256 brp_inc 1 | dbitrate 500000 dsample-point 0.875 | dtq 125 dprop-seg 6 dphase-seg1 7 dphase-seg2 2 dsjw 1 dbrp 5 | mcp251xfd: dtseg1 1..32 dtseg2 1..16 dsjw 1..16 dbrp 1..256 dbrp_inc 1 | tdcv 0..63 tdco 0..63 | clock 40000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tso_max_size 65536 tso_max_segs 65535 gro_max_size 65536 parentbus spi parentdev spi0.0 | $ ip link set can0 up type can bitrate 1000000 dbitrate 4000000 fd on | $ ip -details link show can0 | 3: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10 | link/can promiscuity 0 allmulti 0 minmtu 0 maxmtu 0 | can <FD,TDC-AUTO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0 | bitrate 1000000 sample-point 0.750 | tq 25 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 5 brp 1 | mcp251xfd: tseg1 2..256 tseg2 1..128 sjw 1..128 brp 1..256 brp_inc 1 | dbitrate 4000000 dsample-point 0.700 | dtq 25 dprop-seg 3 dphase-seg1 3 dphase-seg2 3 dsjw 1 dbrp 1 | tdco 7 | mcp251xfd: dtseg1 1..32 dtseg2 1..16 dsjw 1..16 dbrp 1..256 dbrp_inc 1 | tdcv 0..63 tdco 0..63 | clock 40000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tso_max_size 65536 tso_max_segs 65535 gro_max_size 65536 parentbus spi parentdev spi0.0
There has been some confusion about the MCP2518FD using a relative or absolute TDCO due to the datasheet specifying a range of [-64,63]. I have a custom board with a 40 MHz clock and an estimated loop delay of 100 to 216 ns. During testing at a data bit rate of 4 Mbit/s I found that using can_get_relative_tdco() resulted in bus-off errors. The final TDCO value was 1 which corresponds to a 10% SSP in an absolute configuration. This behavior is expected if the TDCO value is really absolute and not relative. Using priv->can.tdc.tdco instead results in a final TDCO of 8, setting the SSP at exactly 80%. This configuration works.
The automatic, manual, and off TDC modes were tested at speeds up to, and including, 8 Mbit/s on real hardware and behave as expected.
Fixes: 55e5b97f003e ("can: mcp25xxfd: add driver for Microchip MCP25xxFD SPI CAN") Reported-by: Kelsey Maes kelsey@vpprocess.com Closes: https://lore.kernel.org/all/C2121586-C87F-4B23-A933-845362C29CA1@vpprocess.c... Reviewed-by: Vincent Mailhol mailhol.vincent@wanadoo.fr Signed-off-by: Kelsey Maes kelsey@vpprocess.com Link: https://patch.msgid.link/20250430161501.79370-1-kelsey@vpprocess.com [mkl: add comment] Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- .../net/can/spi/mcp251xfd/mcp251xfd-core.c | 40 +++++++++++++++---- 1 file changed, 32 insertions(+), 8 deletions(-)
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c index a48996265172f..21ae3a89924e9 100644 --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c @@ -75,6 +75,24 @@ static const struct can_bittiming_const mcp251xfd_data_bittiming_const = { .brp_inc = 1, };
+/* The datasheet of the mcp2518fd (DS20006027B) specifies a range of + * [-64,63] for TDCO, indicating a relative TDCO. + * + * Manual tests have shown, that using a relative TDCO configuration + * results in bus off, while an absolute configuration works. + * + * For TDCO use the max value (63) from the data sheet, but 0 as the + * minimum. + */ +static const struct can_tdc_const mcp251xfd_tdc_const = { + .tdcv_min = 0, + .tdcv_max = 63, + .tdco_min = 0, + .tdco_max = 63, + .tdcf_min = 0, + .tdcf_max = 0, +}; + static const char *__mcp251xfd_get_model_str(enum mcp251xfd_model model) { switch (model) { @@ -510,8 +528,7 @@ static int mcp251xfd_set_bittiming(const struct mcp251xfd_priv *priv) { const struct can_bittiming *bt = &priv->can.bittiming; const struct can_bittiming *dbt = &priv->can.data_bittiming; - u32 val = 0; - s8 tdco; + u32 tdcmod, val = 0; int err;
/* CAN Control Register @@ -575,11 +592,16 @@ static int mcp251xfd_set_bittiming(const struct mcp251xfd_priv *priv) return err;
/* Transmitter Delay Compensation */ - tdco = clamp_t(int, dbt->brp * (dbt->prop_seg + dbt->phase_seg1), - -64, 63); - val = FIELD_PREP(MCP251XFD_REG_TDC_TDCMOD_MASK, - MCP251XFD_REG_TDC_TDCMOD_AUTO) | - FIELD_PREP(MCP251XFD_REG_TDC_TDCO_MASK, tdco); + if (priv->can.ctrlmode & CAN_CTRLMODE_TDC_AUTO) + tdcmod = MCP251XFD_REG_TDC_TDCMOD_AUTO; + else if (priv->can.ctrlmode & CAN_CTRLMODE_TDC_MANUAL) + tdcmod = MCP251XFD_REG_TDC_TDCMOD_MANUAL; + else + tdcmod = MCP251XFD_REG_TDC_TDCMOD_DISABLED; + + val = FIELD_PREP(MCP251XFD_REG_TDC_TDCMOD_MASK, tdcmod) | + FIELD_PREP(MCP251XFD_REG_TDC_TDCV_MASK, priv->can.tdc.tdcv) | + FIELD_PREP(MCP251XFD_REG_TDC_TDCO_MASK, priv->can.tdc.tdco);
return regmap_write(priv->map_reg, MCP251XFD_REG_TDC, val); } @@ -2083,10 +2105,12 @@ static int mcp251xfd_probe(struct spi_device *spi) priv->can.do_get_berr_counter = mcp251xfd_get_berr_counter; priv->can.bittiming_const = &mcp251xfd_bittiming_const; priv->can.data_bittiming_const = &mcp251xfd_data_bittiming_const; + priv->can.tdc_const = &mcp251xfd_tdc_const; priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK | CAN_CTRLMODE_LISTENONLY | CAN_CTRLMODE_BERR_REPORTING | CAN_CTRLMODE_FD | CAN_CTRLMODE_FD_NON_ISO | - CAN_CTRLMODE_CC_LEN8_DLC; + CAN_CTRLMODE_CC_LEN8_DLC | CAN_CTRLMODE_TDC_AUTO | + CAN_CTRLMODE_TDC_MANUAL; set_bit(MCP251XFD_FLAGS_DOWN, priv->flags); priv->ndev = ndev; priv->spi = spi;