linux-kernel - Re: [RFC PATCH v2 0/3] Prefer working VT console over SPCR and device-tree chosen stdout-path

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Date:   Thu, 14 May 2020 08:22:33 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Petr Mladek <pmladek@...e.com>,
        Alper Nebi Yasak <alpernebiyasak@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-serial@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Biggers <ebiggers@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        Grzegorz Halat <ghalat@...hat.com>,
        Lukas Wunner <lukas@...ner.de>,
        Nicolas Pitre <nico@...xnic.net>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [RFC PATCH v2 0/3] Prefer working VT console over SPCR and
 device-tree chosen stdout-path

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.