From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19833C433FE for ; Wed, 26 Oct 2022 08:40:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233301AbiJZIkQ (ORCPT ); Wed, 26 Oct 2022 04:40:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233267AbiJZIkP (ORCPT ); Wed, 26 Oct 2022 04:40:15 -0400 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB5CA2ED55 for ; Wed, 26 Oct 2022 01:40:13 -0700 (PDT) Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=bjornoya.blackshift.org) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1onbxL-0006aO-MH for linux-can@vger.kernel.org; Wed, 26 Oct 2022 10:40:11 +0200 Received: from dspam.blackshift.org (localhost [127.0.0.1]) by bjornoya.blackshift.org (Postfix) with SMTP id 03E6A10A07A for ; Wed, 26 Oct 2022 08:40:10 +0000 (UTC) Received: from hardanger.blackshift.org (unknown [172.20.34.65]) (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) by bjornoya.blackshift.org (Postfix) with ESMTPS id 5ECFF10A064; Wed, 26 Oct 2022 08:40:09 +0000 (UTC) Received: from blackshift.org (localhost [::1]) by hardanger.blackshift.org (OpenSMTPD) with ESMTP id 97b34878; Wed, 26 Oct 2022 08:40:08 +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, "Daniel S. Trevitz" , Marc Kleine-Budde Subject: [PATCH net-next 01/29] can: add termination resistor documentation Date: Wed, 26 Oct 2022 10:39:39 +0200 Message-Id: <20221026084007.1583333-2-mkl@pengutronix.de> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20221026084007.1583333-1-mkl@pengutronix.de> References: <20221026084007.1583333-1-mkl@pengutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-can@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org From: "Daniel S. Trevitz" Add documentation for how to use and setup the switchable termination resistor support for CAN controllers. Signed-off-by: Daniel Trevitz Link: https://lore.kernel.org/all/3441354.44csPzL39Z@daniel6430 Signed-off-by: Marc Kleine-Budde --- Documentation/networking/can.rst | 33 ++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst index ebc822e605f5..90121deef217 100644 --- a/Documentation/networking/can.rst +++ b/Documentation/networking/can.rst @@ -1148,6 +1148,39 @@ tuning on deep embedded systems'. The author is running a MPC603e load without any problems ... +Switchable Termination Resistors +-------------------------------- + +CAN bus requires a specific impedance across the differential pair, +typically provided by two 120Ohm resistors on the farthest nodes of +the bus. Some CAN controllers support activating / deactivating a +termination resistor(s) to provide the correct impedance. + +Query the available resistances:: + + $ ip -details link show can0 + ... + termination 120 [ 0, 120 ] + +Activate the terminating resistor:: + + $ ip link set dev can0 type can termination 120 + +Deactivate the terminating resistor:: + + $ ip link set dev can0 type can termination 0 + +To enable termination resistor support to a can-controller, either +implement in the controller's struct can-priv:: + + termination_const + termination_const_cnt + do_set_termination + +or add gpio control with the device tree entries from +Documentation/devicetree/bindings/net/can/can-controller.yaml + + The Virtual CAN Driver (vcan) ----------------------------- base-commit: a526a3cc9c8d426713f8bebc18ebbe39a8495d82 -- 2.35.1