can: isotp: support dynamic flow control parameters

The ISO15765-2 standard supports to take the PDUs communication parameters
blocksize (BS) and Separation Time minimum (STmin) either from the first
received flow control (FC) "static" or from every received FC "dynamic".

Add a new CAN_ISOTP_DYN_FC_PARMS flag to support dynamic FC parameters.
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20231208165729.3011-1-socketcan@hartkopp.netSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

include/uapi/linux/can/isotp.h

@@ -137,6 +137,7 @@ struct can_isotp_ll_options {
 #define CAN_ISOTP_WAIT_TX_DONE	0x0400	/* wait for tx completion */
 #define CAN_ISOTP_SF_BROADCAST	0x0800	/* 1-to-N functional addressing */
 #define CAN_ISOTP_CF_BROADCAST	0x1000	/* 1-to-N transmission w/o FC */
+#define CAN_ISOTP_DYN_FC_PARMS	0x2000	/* dynamic FC parameters BS/STmin */
 
 /* protocol machine default values */
 

net/can/isotp.c

@@ -381,8 +381,9 @@ static int isotp_rcv_fc(struct isotp_sock *so, struct canfd_frame *cf, int ae)
 		return 1;
 	}
 
-	/* get communication parameters only from the first FC frame */
-	if (so->tx.state == ISOTP_WAIT_FIRST_FC) {
+	/* get static/dynamic communication params from first/every FC frame */
+	if (so->tx.state == ISOTP_WAIT_FIRST_FC ||
+	    so->opt.flags & CAN_ISOTP_DYN_FC_PARMS) {
 		so->txfc.bs = cf->data[ae + 1];
 		so->txfc.stmin = cf->data[ae + 2];