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;
Subject: Re: [RFC PATCH v2 0/3] Prefer working VT console over SPCR and
 device-tree chosen stdout-path
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Petr Mladek <pmladek@suse.com>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        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>
References: <20200430161438.17640-1-alpernebiyasak@gmail.com>
 <20200501013044.GA288759@jagdpanzerIV.localdomain>
 <818ba356-ba35-68de-b7bf-f145a89280f1@gmail.com>
 <CAHp75VeZRwUp+CpOct4dCAQAfyJZBAY7=qSKwRQh935KEMWw+g@mail.gmail.com>
From:   Alper Nebi Yasak <alpernebiyasak@gmail.com>
Message-ID: <3cd630dd-9bb9-e975-7466-c3125aa6afa3@gmail.com>
Date:   Fri, 1 May 2020 18:07:10 +0300
User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
In-Reply-To: <CAHp75VeZRwUp+CpOct4dCAQAfyJZBAY7=qSKwRQh935KEMWw+g@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 01/05/2020 16:16, Andy Shevchenko wrote:
> On Fri, May 1, 2020 at 2:11 PM Alper Nebi Yasak
> <alpernebiyasak@gmail.com> wrote:
>> I'm assuming "by default" here means "without console arguments"
>> regardless of firmware requests. This paragraph (with small changes) is
>> repeated on many other Kconfig descriptions (drivers/tty/serial/Kconfig,
>> drivers/tty/serial/8250/Kconfig, arch/sparc/Kconfig from grepping for
>> '/dev/tty0' on **/Kconfig).
>>
>>  From Documentation/admin-guide/serial-console.rst:
>>
>>> You can specify multiple console= options on the kernel command line.
>>> [...]
>>> Note that you can only define one console per device type (serial, video).
>>>
>>> If no console device is specified, the first device found capable of
>>> acting as a system console will be used. At this time, the system
>>> first looks for a VGA card and then for a serial port. So if you don't
>>> have a VGA card in your system the first serial port will automatically
>>> become the console.
>>
>> and later on:
>>
>>> Note that if you boot without a ``console=`` option (or with
>>> ``console=/dev/tty0``), ``/dev/console`` is the same as ``/dev/tty0``.
>>> In that case everything will still work.
> 
> I'm wondering if behaviour is changed if you put console=tty1 instead
> of console=tty0.

Just tested again with the QEMU aarch64 VM. Comparing console=tty1 and
console=tty0 cases: /proc/consoles has tty1 instead of tty0 (both also
has ttyAMA0), and `echo '/dev/console is here' >>/dev/console` goes to
vt1 instead of the currently visible vt. Same difference before and
after this patchset.