linux-kernel - [PATCH v5 2/3] can: length: fix description of the RRS field

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Message-ID: <PAVPR10MB7209B55BA47D42F2610851BEB15AA@PAVPR10MB7209.EURPRD10.PROD.OUTLOOK.COM>
Date:   Wed, 14 Jun 2023 20:40:36 +0000
From:   HMS Incident Management <Incidentmanagement@....se>
To:     "mkl@...gutronix.de" <mkl@...gutronix.de>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
        "Thomas.Kopp@...rochip.com" <Thomas.Kopp@...rochip.com>
CC:     "socketcan@...tkopp.net" <socketcan@...tkopp.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "marex@...x.de" <marex@...x.de>,
        "simon.horman@...igine.com" <simon.horman@...igine.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mailhol.vincent@...adoo.fr" <mailhol.vincent@...adoo.fr>
Subject: [PATCH v5 2/3] can: length: fix description of the RRS field

**We apologize for the delay in delivering this email, which was caused by a mail incident that occurred over the weekend on June 10th. This email was originally sent from vincent.mailhol@...il.com on 06/11/2023 02:58:14 

The CAN-FD frames only have one reserved bit. The bit corresponding to
Classical CAN frame's RTR bit is called the "Remote Request
Substitution (RRS)" [1].

N.B. The RRS is not to be confused with the Substitute Remote Request
(SRR).

Fix the description in the CANFD_FRAME_OVERHEAD_SFF/EFF macros.

The total remains unchanged, so this is just a documentation fix.

In addition to the above add myself as copyright owner for 2020 (as
coauthor of the initial version, c.f. Fixes tag).

[1] ISO 11898-1:2015 paragraph 10.4.2.3 "Arbitration field":

  RSS bit [only in FD Frames]

    The RRS bit shall be transmitted in FD Frames at the position of
    the RTR bit in Classical Frames. The RRS bit shall be transmitted
    dominant, but receivers shall accept recessive and dominant RRS
    bits.

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Signed-off-by: Vincent Mailhol 
Reviewed-by: Thomas Kopp 
---
 include/linux/can/length.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index b8c12c83bc51..521fdbce2d69 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp 
  * Copyright (C) 2020 Marc Kleine-Budde 
+ * Copyright (C) 2020 Vincent Mailhol 
  */
 
 #ifndef _CAN_LENGTH_H
@@ -64,7 +65,7 @@
  * ---------------------------------------------------------
  * Start-of-frame			1
  * Identifier				11
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Identifier extension bit (IDE)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
@@ -95,7 +96,7 @@
  * Substitute remote request (SRR)	1
  * Identifier extension bit (IDE)	1
  * Identifier B				18
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
  * Bit Rate Switch (BRS)		1
-- 
2.39.3