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 X-Spam-Level: X-Spam-Status: No, score=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 5134BC47080 for ; Tue, 1 Jun 2021 04:49:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22B1861378 for ; Tue, 1 Jun 2021 04:49:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232770AbhFAEvE (ORCPT ); Tue, 1 Jun 2021 00:51:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:35048 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229521AbhFAEvD (ORCPT ); Tue, 1 Jun 2021 00:51:03 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 12B2D61005; Tue, 1 Jun 2021 04:49:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1622522961; bh=E6eMszyR4j43HLBX4pS6cALAerAGNXAaH9kUd/gzZFo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=q5x13V+SKFxYk/dYvmAGs/sVqQ4W+yFASo4BLD0af2gMaXYKX9LADwF4VQIhAM/DB RqcQ8yXLSvtedE+pboogSjCxLbZZh4QhoEFtjjctFF4915RDR2D9MizKi8h4Y293Lq qKt7MzJcQbK2t/vNBl9Q+azSgOO3Re1pO+3hEhUE= Date: Tue, 1 Jun 2021 06:49:18 +0200 From: Greg KH To: "xuyang2018.jy@fujitsu.com" Cc: "linux-serial@vger.kernel.org" Subject: Re: the usage of hardware flow control in serial console Message-ID: References: <60B59E0F.7030609@fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <60B59E0F.7030609@fujitsu.com> Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On Tue, Jun 01, 2021 at 02:39:41AM +0000, xuyang2018.jy@fujitsu.com wrote: > HI All > > I append "console=ttyS0,115200n8r" to my kernel command line and reboot > my system. > > # cat /proc/tty/driver/serial > serinfo:1.0 driver revision: > 0: uart:16550A port:000003F8 irq:4 tx:0 rx:0 RTS|DTR > 1: uart:unknown port:000002F8 irq:3 > 2: uart:unknown port:000003E8 irq:4 > 3: uart:unknown port:000002E8 irq:3 > > then I echo 1 > /dev/ttyS0, but it hangs.(If I don't use r, it works well.) 'echo' is horrible at testing serial port communication. Why not use a real serial terminal program that knows how to set the line settings? > Does it need my console connected with other machine? Something needs to be on the other end of that serial connection for this to work properly, right? > Also, many services become timeout when I use systemctl > restart/status/stop(tx,rx data doesn't increase). > > I just want to check whether it is a usage problem(my system environmet > is centos8). My machine is physical machine and virtual machine doesn't > have this problem(it has RTS|CTS|DTR|DSR|CD flag). Why do you want to use "r" here? What problem are you trying to solve? thanks, greg k-h