From patchwork Mon May 18 14:45:02 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lukas Wunner X-Patchwork-Id: 200401 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6539CC433DF for ; Mon, 18 May 2020 14:47:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C8AC20756 for ; Mon, 18 May 2020 14:47:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727063AbgEROrM (ORCPT ); Mon, 18 May 2020 10:47:12 -0400 Received: from mailout2.hostsharing.net ([83.223.78.233]:45505 "EHLO mailout2.hostsharing.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727938AbgEROrM (ORCPT ); Mon, 18 May 2020 10:47:12 -0400 Received: from h08.hostsharing.net (h08.hostsharing.net [83.223.95.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.hostsharing.net", Issuer "COMODO RSA Domain Validation Secure Server CA" (not verified)) by mailout2.hostsharing.net (Postfix) with ESMTPS id DCDE410189B69; Mon, 18 May 2020 16:47:09 +0200 (CEST) Received: from localhost (pd95be530.dip0.t-ipconnect.de [217.91.229.48]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (No client certificate requested) by h08.hostsharing.net (Postfix) with ESMTPSA id 9A0F8612B6E6; Mon, 18 May 2020 16:47:09 +0200 (CEST) X-Mailbox-Line: From 94c6c800d1ca9fa04766dd1d43a8272c5ad4bedd Mon Sep 17 00:00:00 2001 Message-Id: <94c6c800d1ca9fa04766dd1d43a8272c5ad4bedd.1589811297.git.lukas@wunner.de> In-Reply-To: References: From: Lukas Wunner Date: Mon, 18 May 2020 16:45:02 +0200 Subject: [PATCH v3 2/2] serial: 8250: Support rs485 bus termination GPIO To: Greg Kroah-Hartman , Jiri Slaby , Rob Herring Cc: "Matwey V. Kornilov" , Giulio Benetti , Heiko Stuebner , Andy Shevchenko , Christoph Muellner , Jan Kiszka , linux-serial@vger.kernel.org, devicetree@vger.kernel.org Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Commit e8759ad17d41 ("serial: uapi: Add support for bus termination") introduced the ability to enable rs485 bus termination from user space. So far the feature is only used by a single driver, 8250_exar.c, using a hardcoded GPIO pin specific to Siemens IOT2040 products. Provide for a more generic solution by allowing specification of an rs485 bus termination GPIO pin in the device tree: Amend the serial core to retrieve the GPIO from the device tree (or ACPI table) and amend the default ->rs485_config() callback for 8250 drivers to change the GPIO on request from user space. Perhaps 8250_exar.c can be converted to the generic approach in a follow-up patch. Signed-off-by: Lukas Wunner Reviewed-by: Andy Shevchenko Cc: Jan Kiszka --- drivers/tty/serial/8250/8250_port.c | 3 +++ drivers/tty/serial/serial_core.c | 16 ++++++++++++++++ include/linux/serial_core.h | 2 ++ 3 files changed, 21 insertions(+) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 4d83c85a7389..4f6ff54175ce 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -681,6 +681,9 @@ int serial8250_em485_config(struct uart_port *port, struct serial_rs485 *rs485) memset(rs485->padding, 0, sizeof(rs485->padding)); port->rs485 = *rs485; + gpiod_set_value(port->rs485_term_gpio, + rs485->flags & SER_RS485_TERMINATE_BUS); + /* * Both serial8250_em485_init() and serial8250_em485_destroy() * are idempotent. diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 43b6682877d5..57840cf90388 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -3317,6 +3317,7 @@ int uart_get_rs485_mode(struct uart_port *port) * to get to a defined state with the following properties: */ rs485conf->flags &= ~(SER_RS485_RX_DURING_TX | SER_RS485_ENABLED | + SER_RS485_TERMINATE_BUS | SER_RS485_RTS_AFTER_SEND); rs485conf->flags |= SER_RS485_RTS_ON_SEND; @@ -3331,6 +3332,21 @@ int uart_get_rs485_mode(struct uart_port *port) rs485conf->flags |= SER_RS485_RTS_AFTER_SEND; } + /* + * Disabling termination by default is the safe choice: Else if many + * bus participants enable it, no communication is possible at all. + * Works fine for short cables and users may enable for longer cables. + */ + port->rs485_term_gpio = devm_gpiod_get_optional(dev, "rs485-term", + GPIOD_OUT_LOW); + if (IS_ERR(port->rs485_term_gpio)) { + ret = PTR_ERR(port->rs485_term_gpio); + port->rs485_term_gpio = NULL; + if (ret != -EPROBE_DEFER) + dev_err(dev, "Cannot get rs485-term-gpios\n"); + return ret; + } + return 0; } EXPORT_SYMBOL_GPL(uart_get_rs485_mode); diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index b649a2b894e7..9fd550e7946a 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -10,6 +10,7 @@ #include #include #include +#include #include #include #include @@ -251,6 +252,7 @@ struct uart_port { struct attribute_group *attr_group; /* port specific attributes */ const struct attribute_group **tty_groups; /* all attributes (serial core use only) */ struct serial_rs485 rs485; + struct gpio_desc *rs485_term_gpio; /* enable RS485 bus termination */ struct serial_iso7816 iso7816; void *private_data; /* generic platform data pointer */ };