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 13070C433EF for ; Sat, 4 Jun 2022 09:21:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233935AbiFDJVU (ORCPT ); Sat, 4 Jun 2022 05:21:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52644 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233873AbiFDJVS (ORCPT ); Sat, 4 Jun 2022 05:21:18 -0400 Received: from mx1.molgen.mpg.de (mx3.molgen.mpg.de [141.14.17.11]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3C236377EB; Sat, 4 Jun 2022 02:21:16 -0700 (PDT) Received: from [192.168.0.2] (ip5f5aeb34.dynamic.kabel-deutschland.de [95.90.235.52]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: pmenzel) by mx.molgen.mpg.de (Postfix) with ESMTPSA id 4BA5961EA1938; Sat, 4 Jun 2022 11:21:13 +0200 (CEST) Message-ID: <477007d7-e573-56dd-90de-877eeebd5c4c@molgen.mpg.de> Date: Sat, 4 Jun 2022 11:21:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: Non-working serial console Content-Language: en-US To: Greg KH Cc: linux-serial@vger.kernel.org, LKML References: <1880b7a7-2353-c381-5afb-1d4224eb223b@molgen.mpg.de> From: Paul Menzel In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dear Greg, Am 04.06.22 um 11:04 schrieb Greg KH: > On Thu, Jun 02, 2022 at 11:09:15PM +0200, Paul Menzel wrote: >> Am 02.06.22 um 18:50 schrieb Paul Menzel: >> >>> Since a while I noticed, output to the serial console with >>> `console=ttyS0,115200n8` does not work with the attached configuration >>> `defconfig-non-working-serial.txt` created by `make savedefconfig`. >>> Only, when with `earlyprintk=ttyS0,115200,keep` the serial console >>> starts working. I am able to reproduce it in QEMU. It’s reproducible >>> with Linus’ latest master branch. >>> >>>     $ git log --oneline --no-decorate -1 >>>     8ab2afa23bd19 Merge tag 'for-5.19/fbdev-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev >>>     $ qemu-system-x86_64 --version >>>     QEMU emulator version 5.1.0 >>>     Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers >>>     $ qemu-system-x86_64 -kernel arch/x86/boot/bzImage -append "console=ttyS0,115200n8" -serial file:/dev/shm/kernel.txt -curses >>> >>> With `earlyprintk=` it works: >>> >>>     $ qemu-system-x86_64 -kernel arch/x86/boot/bzImage -append "earlyprintk=serial console=ttyS0,115200n8" -serial file:/dev/shm/kernel.txt -curses >>> >>> Strangely, I found a different configuration, where it works, but I >>> didn’t see what configuration option makes the difference. >>> >>> Can you reproduce the problem with `defconfig-no-working-serial.txt`? >> >> It turns out, the non-working configuration build the serial 8250 driver as >> a module (`CONFIG_SERIAL_8250=m`) instead of building it into the Linux >> kernel. Building it into the Linux kernel and using >> `CONFIG_SERIAL_8250_CONSOLE=y` fixes my issue. > > That makes sense, you need the console to be able to properly send data > out to it :) Indeed. I am still confused, that `earlyprintk=ttyS0,115200,keep` works though despite `CONFIG_SERIAL_8250=m`. Doesn’t that mean, that Linux nevertheless contains some code to initialize the serial console, and send data to it? > Was this a Kconfig change somewhere recently that we messed up the > defaults for? Any chance you can use 'git bisect' to track down the > offending change? No, I guess I made the change several months back to make the Linux kernel image smaller to decrease the boot time. (I have to do measurements again.) Kind regards, Paul