[RFC PATCH v2 3/4] can: canxl: support Remote Request Substitution bit access

[Oliver Hartkopp <socketcan@hartkopp.net>]

The Remote Request Substitution bit is a dominant bit ("0") in the CAN XL
frame. As some CAN XL controllers support to access this bit a new
CANXL_RRS value has been defined for the canxl_frame.flags element.

To read/write the Remote Request Substitution (RRS) bit in the CAN XL
frame the CAN_CTRLMODE_XL_RRS has to be enabled in CAN driver.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 include/uapi/linux/can.h         | 5 ++++-
 include/uapi/linux/can/netlink.h | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h
index e78cbd85ce7c..77d3a940beb0 100644
--- a/include/uapi/linux/can.h
+++ b/include/uapi/linux/can.h
@@ -180,20 +180,23 @@ struct canfd_frame {
 };
 
 /*
  * defined bits for canxl_frame.flags
  *
- * The canxl_frame.flags element contains two bits CANXL_XLF and CANXL_SEC
+ * The canxl_frame.flags element contains three bits CANXL_[XLF|SEC|RRS]
  * and shares the relative position of the struct can[fd]_frame.len element.
  * The CANXL_XLF bit ALWAYS needs to be set to indicate a valid CAN XL frame.
  * As a side effect setting this bit intentionally breaks the length checks
  * for Classical CAN and CAN FD frames.
+ * To read/write the Remote Request Substitution (RRS) bit in the CAN XL
+ * frame the CAN_CTRLMODE_XL_RRS has to be enabled in CAN driver.
  *
  * Undefined bits in canxl_frame.flags are reserved and shall be set to zero.
  */
 #define CANXL_XLF 0x80 /* mandatory CAN XL frame flag (must always be set!) */
 #define CANXL_SEC 0x01 /* Simple Extended Content (security/segmentation) */
+#define CANXL_RRS 0x02 /* Remote Request Substitution */
 
 /* the 8-bit VCID is optionally placed in the canxl_frame.prio element */
 #define CANXL_VCID_OFFSET 16 /* bit offset of VCID in prio element */
 #define CANXL_VCID_VAL_MASK 0xFFUL /* VCID is an 8-bit value */
 #define CANXL_VCID_MASK (CANXL_VCID_VAL_MASK << CANXL_VCID_OFFSET)
diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h
index f4fb8eea8f35..55b8374ab094 100644
--- a/include/uapi/linux/can/netlink.h
+++ b/include/uapi/linux/can/netlink.h
@@ -104,10 +104,11 @@ struct can_ctrlmode {
 #define CAN_CTRLMODE_TDC_AUTO		0x200	/* FD transceiver automatically calculates TDCV */
 #define CAN_CTRLMODE_TDC_MANUAL		0x400	/* FD TDCV is manually set up by user */
 #define CAN_CTRLMODE_XL			0x800	/* CAN XL mode */
 #define CAN_CTRLMODE_XL_TDC_AUTO	0x1000	/* XL transceiver automatically calculates TDCV */
 #define CAN_CTRLMODE_XL_TDC_MANUAL	0x2000	/* XL TDCV is manually set up by user */
+#define CAN_CTRLMODE_XL_RRS		0x4000	/* XL enable RRS bit access */
 
 /*
  * CAN device statistics
  */
 struct can_device_stats {
-- 
2.45.2