netdev - [net-next 04/21] can: uapi: introduce CANFD_FDF flag for mixed content in struct canfd

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Date:   Thu, 27 May 2021 10:45:15 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        kernel@...gutronix.de, Oliver Hartkopp <socketcan@...tkopp.net>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [net-next 04/21] can: uapi: introduce CANFD_FDF flag for mixed content in struct canfd_frame

From: Oliver Hartkopp <socketcan@...tkopp.net>

The struct can_frame and struct canfd_frame intentionally share the
same layout to be able to write CAN frame content into a CAN FD frame
structure. When this is done the former differentiation via CAN_MTU /
CANFD_MTU is lost. CANFD_FDF allows programmers to mark CAN FD frames
in the case of using struct canfd_frame for mixed CAN/CAN FD
content (dual use).

N.B. the Kernel APIs do NOT provide mixed CAN / CAN FD content inside
of struct canfd_frame therefore the CANFD_FDF flag is disregarded by
Linux.

Link: https://lore.kernel.org/r/20170411134343.3089-1-socketcan@hartkopp.net
Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 include/uapi/linux/can.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h
index ac5d7a31671f..90801ada2bbe 100644
--- a/include/uapi/linux/can.h
+++ b/include/uapi/linux/can.h
@@ -135,9 +135,18 @@ struct can_frame {
  * controller only the CANFD_BRS bit is relevant for real CAN controllers when
  * building a CAN FD frame for transmission. Setting the CANFD_ESI bit can make
  * sense for virtual CAN interfaces to test applications with echoed frames.
+ *
+ * The struct can_frame and struct canfd_frame intentionally share the same
+ * layout to be able to write CAN frame content into a CAN FD frame structure.
+ * When this is done the former differentiation via CAN_MTU / CANFD_MTU gets
+ * lost. CANFD_FDF allows programmers to mark CAN FD frames in the case of
+ * using struct canfd_frame for mixed CAN / CAN FD content (dual use).
+ * N.B. the Kernel APIs do NOT provide mixed CAN / CAN FD content inside of
+ * struct canfd_frame therefore the CANFD_FDF flag is disregarded by Linux.
  */
 #define CANFD_BRS 0x01 /* bit rate switch (second bitrate for payload data) */
 #define CANFD_ESI 0x02 /* error state indicator of the transmitting node */
+#define CANFD_FDF 0x04 /* mark CAN FD for dual use of struct canfd_frame */
 
 /**
  * struct canfd_frame - CAN flexible data rate frame structure
-- 
2.30.2