From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from metis.whiteo.stw.pengutronix.de (metis.whiteo.stw.pengutronix.de [185.203.201.7]) (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 349D1314D12 for ; Tue, 14 Oct 2025 14:10:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.203.201.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760451035; cv=none; b=D2hDcwZVDFxu3J7dziozLXB//Ve8admKwSF9r6grCOK3+QZhdP1Dvbx9QzMTfL1oKMdfW61vwFt8Mxi7NFF+HJwdRwbWFoNod13x5KHMmmm3JRoxbUP9yXiZxjJkOFmHoOvihoGLL74XIF3/SGtKcgqPxau3VUAAhDWuW2FDU00= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760451035; c=relaxed/simple; bh=gXat+PGv1u78rWVjmOz0QjCschIiYBwYOHwql3Mg3VY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=B2ypgpDeB3lrO4WHPwYIgz+aMXjmTxnT1ovmlEekcpNwjGKsW7ooUvJ+Pb5QTDstYxKtHvJoPJgvBapC1Nu4B3do7zl4IqZu4ibYyMIFOka2d7+wLpzQ3HQny4ovnCGoPdTdI80Y8ybUMTaNj6AsV9TQqYwZViAw9x2QPwdvEcA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de; spf=pass smtp.mailfrom=pengutronix.de; arc=none smtp.client-ip=185.203.201.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pengutronix.de Received: from drehscheibe.grey.stw.pengutronix.de ([2a0a:edc0:0:c01:1d::a2]) by metis.whiteo.stw.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1v8fjK-0008IN-Ua; Tue, 14 Oct 2025 16:10:22 +0200 Received: from moin.white.stw.pengutronix.de ([2a0a:edc0:0:b01:1d::7b] helo=bjornoya.blackshift.org) by drehscheibe.grey.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1v8fjK-003ZQB-2F; Tue, 14 Oct 2025 16:10:22 +0200 Received: from blackshift.org (p54b152ce.dip0.t-ipconnect.de [84.177.82.206]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) (Authenticated sender: mkl-all@blackshift.org) by smtp.blackshift.org (Postfix) with ESMTPSA id 6DA40485F1D; Tue, 14 Oct 2025 14:10:22 +0000 (UTC) From: Marc Kleine-Budde To: netdev@vger.kernel.org Cc: davem@davemloft.net, kuba@kernel.org, linux-can@vger.kernel.org, kernel@pengutronix.de, Vincent Mailhol , Marc Kleine-Budde Subject: [PATCH net 09/10] can: add Transmitter Delay Compensation (TDC) documentation Date: Tue, 14 Oct 2025 14:17:56 +0200 Message-ID: <20251014122140.990472-10-mkl@pengutronix.de> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251014122140.990472-1-mkl@pengutronix.de> References: <20251014122140.990472-1-mkl@pengutronix.de> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2a0a:edc0:0:c01:1d::a2 X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.whiteo.stw.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: netdev@vger.kernel.org From: Vincent Mailhol 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 Link: https://patch.msgid.link/20251013-can-fd-doc-v2-2-5d53bdc8f2ad@kernel.org Signed-off-by: Marc Kleine-Budde --- Documentation/networking/can.rst | 64 ++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst index ccd321d29a8a..194e305ae973 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 ---------------------- -- 2.51.0