Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <2b67927057455bc91310f88a1952f808339f14cb.camel@kernel.crashing.org>
Subject: Re: [RFC PATCH v2 0/3] Prefer working VT console over SPCR and
 device-tree chosen stdout-path
From:   Benjamin Herrenschmidt <benh@kernel.crashing.org>
To:     Petr Mladek <pmladek@suse.com>,
        Alper Nebi Yasak <alpernebiyasak@gmail.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        linux-serial@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Biggers <ebiggers@google.com>,
        Feng Tang <feng.tang@intel.com>,
        Grzegorz Halat <ghalat@redhat.com>,
        Lukas Wunner <lukas@wunner.de>,
        Nicolas Pitre <nico@fluxnic.net>,
        Sam Ravnborg <sam@ravnborg.org>
Date:   Thu, 14 May 2020 08:22:33 +1000
In-Reply-To: <20200513143755.GM17734@linux-b0ei>
References: <20200430161438.17640-1-alpernebiyasak@gmail.com>
         <20200513143755.GM17734@linux-b0ei>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, 2020-05-13 at 16:37 +0200, Petr Mladek wrote:
> The only common rules are:
> 
>    + The last console on the command line should always be the
>      preferred one when defined.
> 
>    + Consoles defined by the device (SPCR, device tree) are used
>      when there is no commandline.

With the exception that on x86, SPCR is only used for early_con, we
don't do add_preferred_console() at all for it.

I sort-of understand why... the track record on BIOS quality out there
being what it is, I could see this causing a number of systems start
sending the console to a non-existent or non-wired serial port instead
of the tty/gpu because the BIOS leave SPCR set/enabled for no reason.

It may or may not be the case in practice but I don't see how we can
figure that out without either a large campain of data collection from
tons of systems (which will miss plenty) or just taking the chance &
breaking people and see who screams :-)

Cheers,
Ben.