[PATCH v5 4/4] iplink_can: add new CAN FD bittiming parameters: Transmitter Delay Compensation (TDC)

Vincent Mailhol
2021-08-14T10:20:07Z

At high bit rates, the propagation delay from the TX pin to the RX pin
of the transceiver causes measurement errors: the sample point on the
RX pin might occur on the previous bit.

This issue is addressed in ISO 11898-1 section 11.3.3 "Transmitter
delay compensation" (TDC).

This patch brings command line support to nine TDC parameters which
were recently added to the kernel's CAN netlink interface in order to
implement TDC:
- IFLA_CAN_TDC_TDCV_MIN: Transmitter Delay Compensation Value
minimum value
- IFLA_CAN_TDC_TDCV_MAX: Transmitter Delay Compensation Value
maximum value
- IFLA_CAN_TDC_TDCO_MIN: Transmitter Delay Compensation Offset
minimum value
- IFLA_CAN_TDC_TDCO_MAX: Transmitter Delay Compensation Offset
maximum value
- IFLA_CAN_TDC_TDCF_MIN: Transmitter Delay Compensation Filter
window minimum value
- IFLA_CAN_TDC_TDCF_MAX: Transmitter Delay Compensation Filter
window maximum value
- IFLA_CAN_TDC_TDCV: Transmitter Delay Compensation Value
- IFLA_CAN_TDC_TDCO: Transmitter Delay Compensation Offset
- IFLA_CAN_TDC_TDCF: Transmitter Delay Compensation Filter window

All those new parameters are nested together into the attribute
IFLA_CAN_TDC.

A tdc-mode parameter allow to specify how to operate. Valid options
are:

* auto: the transmitter automatically measures TDCV. As such, TDCV
values can not be manually provided. In this mode, the user must
specify TDCO and may also specify TDCF if supported.

* manual: Use the TDCV value provided by the user are used. In this
mode, the user must specify both TDCV and TDCO and may also
specify TDCF if supported.

* off: TDC is explicitly disabled.

* tdc-mode parameter omitted (default mode): the kernel decides
whether TDC should be enabled or not and if so, it calculates the
TDC values. TDC parameters are an expert option and the average
user is not expected to provide those, thus the presence of this
"default mode".

TDCV is always reported in manual mode. In auto mode, TDCV is reported
only if the value is available. Especially, the TDCV might not be
available if the controller has no feature to report it or if the
value in not yet available (i.e. no data sent yet and measurement did
not occur).

TDCF is reported only if tdcf_max is not zero (i.e. if supported by the controller).

For reference, here are a few samples of how the output looks like:

$ ip link set can0 type can bitrate 1000000 dbitrate 8000000 fd on tdco 7 tdcf 8 tdc-mode auto

$ ip --details link show can0
1: can0: <NOARP,ECHO> mtu 72 qdisc noop state DOWN mode DEFAULT group default qlen 10
link/can promiscuity 0 minmtu 0 maxmtu 0
can <FD,TDC_AUTO> state STOPPED (berr-counter tx 0 rx 0) restart-ms 0
bitrate 1000000 sample-point 0.750
tq 12 prop-seg 29 phase-seg1 30 phase-seg2 20 sjw 1 brp 1
ES582.1/ES584.1: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 brp_inc 1
dbitrate 8000000 dsample-point 0.700
dtq 12 dprop-seg 3 dphase-seg1 3 dphase-seg2 3 dsjw 1 dbrp 1
tdco 7 tdcf 8
ES582.1/ES584.1: dtseg1 2..32 dtseg2 1..16 dsjw 1..8 dbrp 1..32 dbrp_inc 1
tdco 0..127 tdcf 0..127
clock 80000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

$ ip --details --json --pretty link show can0
[ {
"ifindex": 1,
"ifname": "can0",
"flags": [ "NOARP","ECHO" ],
"mtu": 72,
"qdisc": "noop",
"operstate": "DOWN",
"linkmode": "DEFAULT",
"group": "default",
"txqlen": 10,
"link_type": "can",
"promiscuity": 0,
"min_mtu": 0,
"max_mtu": 0,
"linkinfo": {
"info_kind": "can",
"info_data": {
"ctrlmode": [ "FD","TDC_AUTO" ],
"state": "STOPPED",
"berr_counter": {
"tx": 0,
"rx": 0
},
"restart_ms": 0,
"bittiming": {
"bitrate": 1000000,
"sample_point": "0.750",
"tq": 12,
"prop_seg": 29,
"phase_seg1": 30,
"phase_seg2": 20,
"sjw": 1,
"brp": 1
},
"bittiming_const": {
"name": "ES582.1/ES584.1",
"tseg1": {
"min": 2,
"max": 256
},
"tseg2": {
"min": 2,
"max": 128
},
"sjw": {
"min": 1,
"max": 128
},
"brp": {
"min": 1,
"max": 512
},
"brp_inc": 1
},
"data_bittiming": {
"bitrate": 8000000,
"sample_point": "0.700",
"tq": 12,
"prop_seg": 3,
"phase_seg1": 3,
"phase_seg2": 3,
"sjw": 1,
"brp": 1,
"tdc": {
"tdco": 7,
"tdcf": 8
}
},
"data_bittiming_const": {
"name": "ES582.1/ES584.1",
"tseg1": {
"min": 2,
"max": 32
},
"tseg2": {
"min": 1,
"max": 16
},
"sjw": {
"min": 1,
"max": 8
},
"brp": {
"min": 1,
"max": 32
},
"brp_inc": 1,
"tdc": {
"tdco": {
"min": 0,
"max": 127
},
"tdcf": {
"min": 0,
"max": 127
}
}
},
"clock": 80000000
}
},
"num_tx_queues": 1,
"num_rx_queues": 1,
"gso_max_size": 65536,
"gso_max_segs": 65535
} ]

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
include/uapi/linux/can/netlink.h | 30 +++++++-
ip/iplink_can.c | 113 +++++++++++++++++++++++++++++++
2 files changed, 140 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h
index 00c763df..258b2d2b 100644
--- a/include/uapi/linux/can/netlink.h
+++ b/include/uapi/linux/can/netlink.h
@@ -101,6 +101,8 @@ struct can_ctrlmode {
#define CAN_CTRLMODE_PRESUME_ACK 0x40 /* Ignore missing CAN ACKs */
#define CAN_CTRLMODE_FD_NON_ISO 0x80 /* CAN FD in non-ISO mode */
#define CAN_CTRLMODE_CC_LEN8_DLC 0x100 /* Classic CAN DLC option */
+#define CAN_CTRLMODE_TDC_AUTO 0x200 /* CAN transiver automatically calculates TDCV */
+#define CAN_CTRLMODE_TDC_MANUAL 0x400 /* TDCV is manually set up by user */

/*
* CAN device statistics
@@ -134,12 +136,34 @@ enum {
IFLA_CAN_BITRATE_CONST,
IFLA_CAN_DATA_BITRATE_CONST,
IFLA_CAN_BITRATE_MAX,
- __IFLA_CAN_MAX
-};
+ IFLA_CAN_TDC,

-#define IFLA_CAN_MAX (__IFLA_CAN_MAX - 1)
+ /* add new constants above here */
+ __IFLA_CAN_MAX,
+ IFLA_CAN_MAX = __IFLA_CAN_MAX - 1
+};

/* u16 termination range: 1..65535 Ohms */
#define CAN_TERMINATION_DISABLED 0

+/*
+ * CAN FD Transmitter Delay Compensation (TDC)
+ */
+enum {
+ IFLA_CAN_TDC_UNSPEC,
+ IFLA_CAN_TDC_TDCV_MIN, /* u32 */
+ IFLA_CAN_TDC_TDCV_MAX, /* u32 */
+ IFLA_CAN_TDC_TDCO_MIN, /* u32 */
+ IFLA_CAN_TDC_TDCO_MAX, /* u32 */
+ IFLA_CAN_TDC_TDCF_MIN, /* u32 */
+ IFLA_CAN_TDC_TDCF_MAX, /* u32 */
+ IFLA_CAN_TDC_TDCV, /* u32 */
+ IFLA_CAN_TDC_TDCO, /* u32 */
+ IFLA_CAN_TDC_TDCF, /* u32 */
+
+ /* add new constants above here */
+ __IFLA_CAN_TDC,
+ IFLA_CAN_TDC_MAX = __IFLA_CAN_TDC - 1
+};
+
#endif /* !_UAPI_CAN_NETLINK_H */
diff --git a/ip/iplink_can.c b/ip/iplink_can.c
index e438e416..e698655d 100644
--- a/ip/iplink_can.c
+++ b/ip/iplink_can.c
@@ -28,6 +28,7 @@ static void print_usage(FILE *f)
"\n"
"\t[ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |\n"
"\t[ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1\n \t dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]\n"
+ "\t[ tdcv TDCV tdco TDCO tdcf TDCF ]\n"
"\n"
"\t[ loopback { on | off } ]\n"
"\t[ listen-only { on | off } ]\n"
@@ -38,6 +39,7 @@ static void print_usage(FILE *f)
"\t[ fd-non-iso { on | off } ]\n"
"\t[ presume-ack { on | off } ]\n"
"\t[ cc-len8-dlc { on | off } ]\n"
+ "\t[ tdc-mode { auto | manual | off } ]\n"
"\n"
"\t[ restart-ms TIME-MS ]\n"
"\t[ restart ]\n"
@@ -51,6 +53,9 @@ static void print_usage(FILE *f)
"\t PHASE-SEG1 := { NUMBER in tq }\n"
"\t PHASE-SEG2 := { NUMBER in tq }\n"
"\t SJW := { NUMBER in tq }\n"
+ "\t TDCV := { NUMBER in tc}\n"
+ "\t TDCO := { NUMBER in tc}\n"
+ "\t TDCF := { NUMBER in tc}\n"
"\t RESTART-MS := { 0 | NUMBER in ms }\n"
);
}
@@ -105,6 +110,8 @@ static void print_ctrlmode(FILE *f, __u32 cm)
_PF(CAN_CTRLMODE_FD_NON_ISO, "FD-NON-ISO");
_PF(CAN_CTRLMODE_PRESUME_ACK, "PRESUME-ACK");
_PF(CAN_CTRLMODE_CC_LEN8_DLC, "CC-LEN8-DLC");
+ _PF(CAN_CTRLMODE_TDC_AUTO, "TDC_AUTO");
+ _PF(CAN_CTRLMODE_TDC_MANUAL, "TDC_MANUAL");
#undef _PF
if (cm)
print_hex(PRINT_ANY, NULL, "%x", cm);
@@ -116,6 +123,8 @@ static int can_parse_opt(struct link_util *lu, int argc, char **argv,
{
struct can_bittiming bt = {}, dbt = {};
struct can_ctrlmode cm = {0, 0};
+ struct rtattr *tdc;
+ __u32 tdcv = -1, tdco = -1, tdcf = -1;

while (argc > 0) {
if (matches(*argv, "bitrate") == 0) {
@@ -181,6 +190,18 @@ static int can_parse_opt(struct link_util *lu, int argc, char **argv,
NEXT_ARG();
if (get_u32(&dbt.sjw, *argv, 0))
invarg("invalid \"dsjw\" value\n", *argv);
+ } else if (matches(*argv, "tdcv") == 0) {
+ NEXT_ARG();
+ if (get_u32(&tdcv, *argv, 0))
+ invarg("invalid \"tdcv\" value\n", *argv);
+ } else if (matches(*argv, "tdco") == 0) {
+ NEXT_ARG();
+ if (get_u32(&tdco, *argv, 0))
+ invarg("invalid \"tdco\" value\n", *argv);
+ } else if (matches(*argv, "tdcf") == 0) {
+ NEXT_ARG();
+ if (get_u32(&tdcf, *argv, 0))
+ invarg("invalid \"tdcf\" value\n", *argv);
} else if (matches(*argv, "loopback") == 0) {
NEXT_ARG();
set_ctrlmode("loopback", *argv, &cm,
@@ -217,6 +238,23 @@ static int can_parse_opt(struct link_util *lu, int argc, char **argv,
NEXT_ARG();
set_ctrlmode("cc-len8-dlc", *argv, &cm,
CAN_CTRLMODE_CC_LEN8_DLC);
+ } else if (matches(*argv, "tdc-mode") == 0) {
+ NEXT_ARG();
+ if (strcmp(*argv, "auto") == 0) {
+ cm.flags |= CAN_CTRLMODE_TDC_AUTO;
+ cm.mask |= CAN_CTRLMODE_TDC_AUTO;
+ } else if (strcmp(*argv, "manual") == 0) {
+ cm.flags |= CAN_CTRLMODE_TDC_MANUAL;
+ cm.mask |= CAN_CTRLMODE_TDC_MANUAL;
+ } else if (strcmp(*argv, "off") == 0) {
+ cm.mask |= CAN_CTRLMODE_TDC_AUTO |
+ CAN_CTRLMODE_TDC_MANUAL;
+ } else {
+ fprintf(stderr,
+ "Error: argument of \"tdc-mode\" must be \"auto\", \"manual\" or \"off\", not \"%s\"\n",
+ *argv);
+ exit (-1);
+ }
} else if (matches(*argv, "restart") == 0) {
__u32 val = 1;

@@ -254,6 +292,17 @@ static int can_parse_opt(struct link_util *lu, int argc, char **argv,
if (cm.mask)
addattr_l(n, 1024, IFLA_CAN_CTRLMODE, &cm, sizeof(cm));

+ if (tdcv != -1 || tdco != -1 || tdcf != -1) {
+ tdc = addattr_nest(n, 1024, IFLA_CAN_TDC | NLA_F_NESTED);
+ if (tdcv != -1)
+ addattr32(n, 1024, IFLA_CAN_TDC_TDCV, tdcv);
+ if (tdco != -1)
+ addattr32(n, 1024, IFLA_CAN_TDC_TDCO, tdco);
+ if (tdcf != -1)
+ addattr32(n, 1024, IFLA_CAN_TDC_TDCF, tdcf);
+ addattr_nest_end(n, tdc);
+ }
+
return 0;
}

@@ -282,6 +331,62 @@ static void can_print_timing_min_max(const char *json_attr, const char *fp_attr,
close_json_object();
}

+static void can_print_tdc_opt(FILE *f, struct rtattr *tdc_attr)
+{
+ struct rtattr *tb[IFLA_CAN_TDC_MAX + 1];
+
+ parse_rtattr_nested(tb, IFLA_CAN_TDC_MAX, tdc_attr);
+ if (tb[IFLA_CAN_TDC_TDCV] || tb[IFLA_CAN_TDC_TDCO] ||
+ tb[IFLA_CAN_TDC_TDCF]) {
+ open_json_object("tdc");
+ can_print_nl_indent();
+ if (tb[IFLA_CAN_TDC_TDCV]) {
+ __u32 *tdcv = RTA_DATA(tb[IFLA_CAN_TDC_TDCV]);
+
+ print_uint(PRINT_ANY, "tdcv", " tdcv %u", *tdcv);
+ }
+ if (tb[IFLA_CAN_TDC_TDCO]) {
+ __u32 *tdco = RTA_DATA(tb[IFLA_CAN_TDC_TDCO]);
+
+ print_uint(PRINT_ANY, "tdco", " tdco %u", *tdco);
+ }
+ if (tb[IFLA_CAN_TDC_TDCF]) {
+ __u32 *tdcf = RTA_DATA(tb[IFLA_CAN_TDC_TDCF]);
+
+ print_uint(PRINT_ANY, "tdcf", " tdcf %u", *tdcf);
+ }
+ close_json_object();
+ }
+}
+
+static void can_print_tdc_const_opt(FILE *f, struct rtattr *tdc_attr)
+{
+ struct rtattr *tb[IFLA_CAN_TDC_MAX + 1];
+
+ parse_rtattr_nested(tb, IFLA_CAN_TDC_MAX, tdc_attr);
+ open_json_object("tdc");
+ can_print_nl_indent();
+ if (tb[IFLA_CAN_TDC_TDCV_MIN] && tb[IFLA_CAN_TDC_TDCV_MAX]) {
+ __u32 *tdcv_min = RTA_DATA(tb[IFLA_CAN_TDC_TDCV_MIN]);
+ __u32 *tdcv_max = RTA_DATA(tb[IFLA_CAN_TDC_TDCV_MAX]);
+
+ can_print_timing_min_max("tdcv", " tdcv", *tdcv_min, *tdcv_max);
+ }
+ if (tb[IFLA_CAN_TDC_TDCO_MIN] && tb[IFLA_CAN_TDC_TDCO_MAX]) {
+ __u32 *tdco_min = RTA_DATA(tb[IFLA_CAN_TDC_TDCO_MIN]);
+ __u32 *tdco_max = RTA_DATA(tb[IFLA_CAN_TDC_TDCO_MAX]);
+
+ can_print_timing_min_max("tdco", " tdco", *tdco_min, *tdco_max);
+ }
+ if (tb[IFLA_CAN_TDC_TDCF_MIN] && tb[IFLA_CAN_TDC_TDCF_MAX]) {
+ __u32 *tdcf_min = RTA_DATA(tb[IFLA_CAN_TDC_TDCF_MIN]);
+ __u32 *tdcf_max = RTA_DATA(tb[IFLA_CAN_TDC_TDCF_MAX]);
+
+ can_print_timing_min_max("tdcf", " tdcf", *tdcf_min, *tdcf_max);
+ }
+ close_json_object();
+}
+
static void can_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
{
if (!tb)
@@ -413,6 +518,10 @@ static void can_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
dbt->phase_seg2);
print_uint(PRINT_ANY, "sjw", " dsjw %u", dbt->sjw);
print_uint(PRINT_ANY, "brp", " dbrp %u", dbt->brp);
+
+ if (tb[IFLA_CAN_TDC])
+ can_print_tdc_opt(f, tb[IFLA_CAN_TDC]);
+
close_json_object();
}

@@ -433,6 +542,10 @@ static void can_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
can_print_timing_min_max("brp", " dbrp",
dbtc->brp_min, dbtc->brp_max);
print_uint(PRINT_ANY, "brp_inc", " dbrp_inc %u", dbtc->brp_inc);
+
+ if (tb[IFLA_CAN_TDC])
+ can_print_tdc_const_opt(f, tb[IFLA_CAN_TDC]);
+
close_json_object();
}

--
2.31.1