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 0F8DAC00140 for ; Wed, 24 Aug 2022 12:02:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236618AbiHXMCr (ORCPT ); Wed, 24 Aug 2022 08:02:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50876 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236657AbiHXMCn (ORCPT ); Wed, 24 Aug 2022 08:02:43 -0400 Received: from mga06.intel.com (mga06b.intel.com [134.134.136.31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2DA432D99; Wed, 24 Aug 2022 05:02:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1661342561; x=1692878561; h=date:from:to:cc:subject:in-reply-to:message-id: references:mime-version; bh=CrWyZLJD2SRdNlJrJZciJFk6p2Q2ugSTZKjZU9gzjJ4=; b=nawCodA2IvAmgPyxTUNGTRJjZgxk9n43KY+CAw9shzjvMc+Ak4OubF3I Bqnjz46iIAyY0OQ07xikid/4El63IjPddgvBQVweWHQssHotbs2XCebqO K4gYBaB0hQoNShZ7Z/f+Ir+CXxx+PwyDBqx4B1iDQ7JKTkps7bTMADwtJ j8g5lHZaXGsSxUD+O6mqaKyVLeQL+nk+CQiFF2Mm0l0jNUu8x+jWxBArP o5SQoVVL+DdG3/BoMAfPha+TfNmxTqzktG11zEL190byq4UtIejHK2Ogx ZBoZmzphUarYk9uDzNshEOFTs5HcL3+7noUy2HtrKooPXUgqQ8WtyRvb1 Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10448"; a="355672888" X-IronPort-AV: E=Sophos;i="5.93,260,1654585200"; d="scan'208";a="355672888" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Aug 2022 05:02:41 -0700 X-IronPort-AV: E=Sophos;i="5.93,260,1654585200"; d="scan'208";a="670474495" Received: from cdenk-mobl.ger.corp.intel.com ([10.252.40.24]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Aug 2022 05:02:36 -0700 Date: Wed, 24 Aug 2022 15:02:30 +0300 (EEST) From: =?ISO-8859-15?Q?Ilpo_J=E4rvinen?= To: Sergiu Moga cc: richard.genoud@gmail.com, Greg Kroah-Hartman , Jiri Slaby , nicolas.ferre@microchip.com, alexandre.belloni@bootlin.com, claudiu.beznea@microchip.com, rmk+kernel@arm.linux.org.uk, claudio@evidence.eu.com, rick@efn.org, michael@evidence.eu.com, ryan@bluewatersys.com, linux-serial , linux-arm-kernel@lists.infradead.org, LKML Subject: Re: [PATCH] tty: serial: atmel: Preserve previous USART mode if RS485 disabled In-Reply-To: <20220824114255.444655-1-sergiu.moga@microchip.com> Message-ID: <2cab23a2-7a82-9321-dca1-5c7c71484ad@linux.intel.com> References: <20220824114255.444655-1-sergiu.moga@microchip.com> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="8323329-121819602-1661342560=:1558" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-121819602-1661342560=:1558 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 8BIT On Wed, 24 Aug 2022, Sergiu Moga wrote: > Whenever the atmel_rs485_config driver method would be called, > the USART mode is reset to normal mode before even checking if > RS485 flag is set, thus resulting in losing the previous USART > mode in the case where the checking fails. Some tools, such as > `linux-serial-test`, lead to the driver calling this method > when doing the setup of the serial port: after setting the port > mode (Hardware Flow Control, Normal Mode, RS485 Mode, etc.), > `linux-serial-test` tries to enable/disable RS485 depending on > the commandline arguments passed. If we were to, for example, enable > Hardware Flow Control through `linux-serial-test`, the tool would > make the driver set the corresponding bit to 1 (ATMEL_US_USMODE_HWHS > bit in the ATMEL_US_MR register) through the atmel_set_termios method > and then proceed to disabling RS485. This, in turn, causes the > ATMEL_US_USMODE_HWHS bit of the ATMEL_US_MR mode register to be unset > and, if the checking for RS485 fails, leads to having the mode set > back to the ATMEL_US_USMODE_NORMAL normal mode. Since in hardware > flow control mode the meanings of the ATMEL_US_RTSDIS and > ATMEL_US_RTSEN bits are swapped, this leads to our endpoint leaving > the RTS line to high when wanting to receive, which is the opposite > of what the other endpoint is expecting in order to start transmitting. > This fix ensures that this reset is done only if the checking for RS485 > succeeds. Could you please try to split this long paragraph to a slightly shorter bits such that it would be easier to read. > Fixes: e8faff7330a35 ("ARM: 6092/1: atmel_serial: support for RS485 communications") > Signed-off-by: Sergiu Moga > --- > drivers/tty/serial/atmel_serial.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c > index 0a0b46ee0955..c29b1fb48694 100644 > --- a/drivers/tty/serial/atmel_serial.c > +++ b/drivers/tty/serial/atmel_serial.c > @@ -298,9 +298,6 @@ static int atmel_config_rs485(struct uart_port *port, struct ktermios *termios, > > mode = atmel_uart_readl(port, ATMEL_US_MR); > > - /* Resetting serial mode to RS232 (0x0) */ > - mode &= ~ATMEL_US_USMODE; > - > if (rs485conf->flags & SER_RS485_ENABLED) { > dev_dbg(port->dev, "Setting UART to RS485\n"); > if (rs485conf->flags & SER_RS485_RX_DURING_TX) > @@ -310,6 +307,7 @@ static int atmel_config_rs485(struct uart_port *port, struct ktermios *termios, > > atmel_uart_writel(port, ATMEL_US_TTGR, > rs485conf->delay_rts_after_send); > + mode &= ~ATMEL_US_USMODE; > mode |= ATMEL_US_USMODE_RS485; > } else { > dev_dbg(port->dev, "Setting UART to RS232\n"); > Makes sense. Reviewed-by: Ilpo Järvinen Unrelated to this patch but I came across it while reviewing yours... Do you BTW have any idea why atmel_serial_probe() sets ATMEL_US_USMODE_NORMAL inside rs485_enabled block? I'd have expected it wanted to do ATMEL_US_USMODE_RS485 there too like is done in atmel_config_rs485(). -- i. --8323329-121819602-1661342560=:1558--