[RFC PATCH 1/1] iplink_can: add CAN FD support for FD-COMMON-BRP

[Stefan Mätje <stefan.maetje@xxxxxx>]

Request with CAN_CTRLMODE_FD_COMMON_BRP for CAN FD the usage of a common
BRP for both nominal and the data bit rate. This is on the one hand a
request to the kernel bit rate calculation algorithm. On the other hand
drivers for CAN controllers with only a single BRP register can enforce
the usage of a common BRP for both bit rates by setting this control
mode statically.

Using a common BRP for both (nominal and data) bit rates reduces the
phase tolerance and thus increases the resistance to interference,
thereby reducing the probability of errors (need for a retransmission)
on the CAN bus.

Signed-off-by: Stefan Mätje <stefan.maetje@xxxxxx>
---
 include/uapi/linux/can/netlink.h | 7 ++++---
 ip/iplink_can.c                  | 6 ++++++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h
index 8ec98c21..cfcb4205 100644
--- a/include/uapi/linux/can/netlink.h
+++ b/include/uapi/linux/can/netlink.h
@@ -16,8 +16,8 @@
  * GNU General Public License for more details.
  */
 
-#ifndef _CAN_NETLINK_H
-#define _CAN_NETLINK_H
+#ifndef _UAPI_CAN_NETLINK_H
+#define _UAPI_CAN_NETLINK_H
 
 #include <linux/types.h>
 
@@ -101,8 +101,9 @@ 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_AUTO		0x200	/* CAN controller automatically calculates TDCV */
 #define CAN_CTRLMODE_TDC_MANUAL		0x400	/* TDCV is manually set up by user */
+#define CAN_CTRLMODE_FD_COMMON_BRP	0x800	/* CAN FD common BRP for nom and data bitrates */
 
 /*
  * CAN device statistics
diff --git a/ip/iplink_can.c b/ip/iplink_can.c
index fcffa852..186e145a 100644
--- a/ip/iplink_can.c
+++ b/ip/iplink_can.c
@@ -42,6 +42,7 @@ static void print_usage(FILE *f)
 		"\t[ presume-ack { on | off } ]\n"
 		"\t[ cc-len8-dlc { on | off } ]\n"
 		"\t[ tdc-mode { auto | manual | off } ]\n"
+		"\t[ fd-common-brp { on | off } ]\n"
 		"\n"
 		"\t[ restart-ms TIME-MS ]\n"
 		"\t[ restart ]\n"
@@ -122,6 +123,7 @@ static void print_ctrlmode(enum output_type t, __u32 flags, const char* key)
 	print_flag(t, &flags, CAN_CTRLMODE_CC_LEN8_DLC, "CC-LEN8-DLC");
 	print_flag(t, &flags, CAN_CTRLMODE_TDC_AUTO, "TDC-AUTO");
 	print_flag(t, &flags, CAN_CTRLMODE_TDC_MANUAL, "TDC-MANUAL");
+	print_flag(t, &flags, CAN_CTRLMODE_FD_COMMON_BRP, "FD-COMMON-BRP");
 
 	if (flags)
 		print_hex(t, NULL, "%x", flags);
@@ -263,6 +265,10 @@ static int can_parse_opt(struct link_util *lu, int argc, char **argv,
 				invarg("\"tdc-mode\" must be either of \"auto\", \"manual\" or \"off\"",
 					*argv);
 			}
+		} else if (matches(*argv, "fd-common-brp") == 0) {
+			NEXT_ARG();
+			set_ctrlmode("fd-common-brp", *argv, &cm,
+				     CAN_CTRLMODE_FD_COMMON_BRP);
 		} else if (matches(*argv, "restart") == 0) {
 			__u32 val = 1;
 
-- 
2.34.1