From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9F0062FE57F; Mon, 13 Oct 2025 10:10:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760350247; cv=none; b=PAdTYshjPylpsNWuJlKYw5HraTAHVGedaxYPb9jqHLTz5+ifF6YWkEigHsB7UwFza2eLvTlIb4OK4NrmeEPqO7orBWdaH/QzvfVS77SR9WNAUcDGD+Lwzij2lUgrqdOFuBqQwh/G6Hc3xVuEhESY88mWDqzG07fjQMesp1+3msA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760350247; c=relaxed/simple; bh=UXzW5+EctH3GaFeqw4m/HhrRryx1k8DJ0dDcoUah8xg=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=GzOxX/T1t0XZlAl6ghpLyHr16u67IE6s8rzdj6+8punxQrPl0cJt0aRPxP5qg2BJ6GFUtVzBfCvVs85S00YiquAu8kdLE7t+/9fTAsLXciFqrQcdoKaX3Y8FKcUvBLYMVA+mbcwT6vhbGnAY+HgRF8KwlIpXCAk8NnUUCVI5dHs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mUpr6Wn3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mUpr6Wn3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 58297C4CEF8; Mon, 13 Oct 2025 10:10:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760350246; bh=UXzW5+EctH3GaFeqw4m/HhrRryx1k8DJ0dDcoUah8xg=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=mUpr6Wn3wEwNmfRWTcCDPR9qBkGsLByCHTnO8wEBFyQz002ZOEc+ATiPb9KrfIfaS U7JDXz0GGUfRmZSewTmt8nPDyKYvlugTmuXNkYZelSYSOVmQM5Z2dS08rAOf4YKKkG xDWRTGSgzAPoDH4SWDDGkijlF5OIzXupsjn1cC8wBG+EwxX6yiLQ1CQM7TBgrXGodl rvkWQDlC+FdISZ8Y/j2l+fBqtesYgzfzmDDRvT9fxucXqP9OBDVpYbH3BeTvUF10EA n3F+/fxyJIm0KgwRPWPvc/KdGe86Y9EKNsaCep0eSkhk9W/iJdcCwsyGTLWx7rjWcG RSk8fYjMLaQjQ== From: Vincent Mailhol Date: Mon, 13 Oct 2025 19:10:23 +0900 Subject: [PATCH v2 2/2] can: add Transmitter Delay Compensation (TDC) documentation Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251013-can-fd-doc-v2-2-5d53bdc8f2ad@kernel.org> References: <20251013-can-fd-doc-v2-0-5d53bdc8f2ad@kernel.org> In-Reply-To: <20251013-can-fd-doc-v2-0-5d53bdc8f2ad@kernel.org> To: Oliver Hartkopp , Marc Kleine-Budde Cc: Simon Horman , Paolo Abeni , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Geert Uytterhoeven , linux-can@vger.kernel.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Vincent Mailhol X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=4385; i=mailhol@kernel.org; h=from:subject:message-id; bh=UXzW5+EctH3GaFeqw4m/HhrRryx1k8DJ0dDcoUah8xg=; b=owGbwMvMwCV2McXO4Xp97WbG02pJDBlvLshEZ82oMnB4mHZp5fn1PQd2WyjZH+RsLJ06cVpT+ KtTcvuLO0pZGMS4GGTFFFmWlXNyK3QUeocd+msJM4eVCWQIAxenAEzkKgMjwxGdN+u3PFBPYMjd mGS61XvX7/TgGW3Tr1gwTPp890jKrTxGhg8Hs3aFpmn+O7m378sHZa6XXcEHJYuURUyOtrvoO6/ kZwEA X-Developer-Key: i=mailhol@kernel.org; a=openpgp; fpr=ED8F700574E67F20E574E8E2AB5FEB886DBB99C2 Back in 2021, support for CAN TDC was added to the kernel in series [1] and in iproute2 in series [2]. However, the documentation was never updated. Add a new sub-section under CAN-FD driver support to document how to configure the TDC using the "ip tool". [1] add the netlink interface for CAN-FD Transmitter Delay Compensation (TDC) Link: https://lore.kernel.org/all/20210918095637.20108-1-mailhol.vincent@wanadoo.fr/ [2] iplink_can: cleaning, fixes and adding TDC support Link: https://lore.kernel.org/all/20211103164428.692722-1-mailhol.vincent@wanadoo.fr/ Signed-off-by: Vincent Mailhol --- Changes in v2: - Fix below "make htmldocs" error: can.rst:1484: ERROR: Unexpected indentation. [docutils] - Change from "Bullet lists" to "Definition lists" format. Link to v1: https://lore.kernel.org/all/20251012-can-fd-doc-v1-2-86cc7d130026@kernel.org/ --- Documentation/networking/can.rst | 64 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst index 58c026d51d94..536ff411da1d 100644 --- a/Documentation/networking/can.rst +++ b/Documentation/networking/can.rst @@ -1464,6 +1464,70 @@ Example when 'fd-non-iso on' is added on this switchable CAN FD adapter:: can state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0 +Transmitter Delay Compensation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +At high bit rates, the propagation delay from the TX pin to the RX pin of +the transceiver might become greater than the actual bit time causing +measurement errors: the RX pin would still be measuring the previous bit. + +The Transmitter Delay Compensation (thereafter, TDC) resolves this problem +by introducing a Secondary Sample Point (SSP) equal to the distance, in +minimum time quantum, from the start of the bit time on the TX pin to the +actual measurement on the RX pin. The SSP is calculated as the sum of two +configurable values: the TDC Value (TDCV) and the TDC offset (TDCO). + +TDC, if supported by the device, can be configured together with CAN-FD +using the ip tool's "tdc-mode" argument as follow: + +**omitted** + When no "tdc-mode" option is provided, the kernel will automatically + decide whether TDC should be turned on, in which case it will + calculate a default TDCO and use the TDCV as measured by the + device. This is the recommended method to use TDC. + +**"tdc-mode off"** + TDC is explicitly disabled. + +**"tdc-mode auto"** + The user must provide the "tdco" argument. The TDCV will be + automatically calculated by the device. This option is only + available if the device supports the TDC-AUTO CAN controller mode. + +**"tdc-mode manual"** + The user must provide both the "tdco" and "tdcv" arguments. This + option is only available if the device supports the TDC-MANUAL CAN + controller mode. + +Note that some devices may offer an additional parameter: "tdcf" (TDC Filter +window). If supported by your device, this can be added as an optional +argument to either "tdc-mode auto" or "tdc-mode manual". + +Example configuring a 500 kbit/s arbitration bitrate, a 5 Mbit/s data +bitrate, a TDCO of 15 minimum time quantum and a TDCV automatically measured +by the device:: + + $ ip link set can0 up type can bitrate 500000 \ + fd on dbitrate 4000000 \ + tdc-mode auto tdco 15 + $ ip -details link show can0 + 5: can0: mtu 72 qdisc pfifo_fast state UP \ + mode DEFAULT group default qlen 10 + link/can promiscuity 0 allmulti 0 minmtu 72 maxmtu 72 + can state ERROR-ACTIVE restart-ms 0 + bitrate 500000 sample-point 0.875 + tq 12 prop-seg 69 phase-seg1 70 phase-seg2 20 sjw 10 brp 1 + ES582.1/ES584.1: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 \ + brp_inc 1 + dbitrate 4000000 dsample-point 0.750 + dtq 12 dprop-seg 7 dphase-seg1 7 dphase-seg2 5 dsjw 2 dbrp 1 + tdco 15 tdcf 0 + ES582.1/ES584.1: dtseg1 2..32 dtseg2 1..16 dsjw 1..8 dbrp 1..32 \ + dbrp_inc 1 + tdco 0..127 tdcf 0..127 + clock 80000000 + + Supported CAN Hardware ---------------------- -- 2.49.1