From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761550AbcKDNWZ (ORCPT ); Fri, 4 Nov 2016 09:22:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55266 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755107AbcKDNWX (ORCPT ); Fri, 4 Nov 2016 09:22:23 -0400 Subject: Re: [REGRESSION] "console: don't prefer first registered if DT specifies stdout-path" breaks console on video outputs of various ARM boards To: Paul Burton References: <20161104121135.4780-1-hdegoede@redhat.com> <17833033.PtOSTzKXGD@np-p-burton> Cc: Linus Torvalds , Andrew Morton , Rob Herring , Frank Rowand , Thorsten Leemhuis , Greg Kroah-Hartman , Tejun Heo , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org From: Hans de Goede Message-ID: Date: Fri, 4 Nov 2016 14:22:17 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <17833033.PtOSTzKXGD@np-p-burton> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 04 Nov 2016 13:22:22 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 04-11-16 13:30, Paul Burton wrote: > Hi Hans, > > On Friday, 4 November 2016 13:11:34 GMT Hans de Goede wrote: >> Hi All, >> >> While booting 4.9-rc# for the first time on an Allwinner A33 tablet, >> I noticed that after u-boot the LCD display stayed black. It turns out >> that there was an issue which caused X to never get up, and all kernel >> (and other startup) messages prior to that only went to ttyS0 which >> consists of 2 tiny testpads on the PCB with this tablet. >> >> The same issue will also happen on any ARM boards which have a HDMI or >> composite video output and which use a stdout-path pointing to their >> serial console. I think this will e.g. also impact the Raspberry Pi, >> I know for certain that this will impact the 99 different Allwinnner >> boards currently supported by mainline u-boot + the mainline kernel. >> >> This is a behavior changes from previous kernels and I consider this >> a regression. Thus I propose to revert the commit in question, for more >> info here is a partial copy of the commit message of the proposed revert: >> >> The reverted commit changes existing behavior on which many ARM boards >> rely. Many ARM small-board-computers, like e.g. the Raspberry Pi have >> both a video output and a serial console. Depending on whether the user >> is using the device as a more regular computer; or as a headless device >> we need to have the console on either one or the other. >> >> Many users rely on the kernel behavior of the console being present on >> both outputs, before the reverted commit the console setup with no >> console= kernel arguments on an ARM board which sets stdout-path in dt >> would look like this: >> >> [root@localhost ~]# cat /proc/consoles >> ttyS0 -W- (EC p a) 4:64 >> tty0 -WU (E p ) 4:1 >> >> Where as after the reverted commit, it looks like this: >> >> [root@localhost ~]# cat /proc/consoles >> ttyS0 -W- (EC p a) 4:64 >> >> This commit reverts commit 05fd007e4629 ("console: don't prefer first >> registered if DT specifies stdout-path") restoring the original behavior. >> >> Regards, >> >> Hans > > Ugh... so the devices you're talking about rely upon set stdout-path in their > device tree but effectively rely upon us ignoring it? No they rely on the kernel using stdout-path as an extra console while keeping tty0 as console, not ignoring it. This how stdout-path has always worked (at least as long as the Allwinner boards have used it, which has been 2 - 3 years now). If you want only the console specified by stdout-path you can get this by specifying it with console=... on the kernel cmdline. > If that's the case then I guess reverting is probably the best option, but it > does restore us to a position where we honor stdout-path for earlycon & then > essentially ignore it for the proper kernel console. That seems pretty bust to > me... We do not ignore it, we use both the tty pointed to by stdout-path and tty0. Regards, Hans