netdev - [PATCH net-next 27/29] can: error: specify the values of data[5..7] of CAN error frames

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Message-Id: <20220720081034.3277385-28-mkl@pengutronix.de>
Date:   Wed, 20 Jul 2022 10:10:32 +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,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH net-next 27/29] can: error: specify the values of data[5..7] of CAN error frames

From: Vincent Mailhol <mailhol.vincent@...adoo.fr>

Currently, data[5..7] of struct can_frame, when used as a CAN error
frame, are defined as being "controller specific". Device specific
behaviours are problematic because it prevents someone from writing
code which is portable between devices.

As a matter of fact, data[5] is never used, data[6] is always used to
report TX error counter and data[7] is always used to report RX error
counter. can-utils also relies on this.

This patch updates the comment in the uapi header to specify that
data[5] is reserved (and thus should not be used) and that data[6..7]
are used for error counters.

Fixes: 0d66548a10cb ("[CAN]: Add PF_CAN core module")
Link: https://lore.kernel.org/all/20220719143550.3681-11-mailhol.vincent@wanadoo.fr
Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 include/uapi/linux/can/error.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/can/error.h b/include/uapi/linux/can/error.h
index 34633283de64..a1000cb63063 100644
--- a/include/uapi/linux/can/error.h
+++ b/include/uapi/linux/can/error.h
@@ -120,6 +120,9 @@
 #define CAN_ERR_TRX_CANL_SHORT_TO_GND  0x70 /* 0111 0000 */
 #define CAN_ERR_TRX_CANL_SHORT_TO_CANH 0x80 /* 1000 0000 */
 
-/* controller specific additional information / data[5..7] */
+/* data[5] is reserved (do not use) */
+
+/* TX error counter / data[6] */
+/* RX error counter / data[7] */
 
 #endif /* _UAPI_CAN_ERROR_H */
-- 
2.35.1