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 <andriy.shevchenko@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Petr Mladek <pmladek@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>,
        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>
 <20200430164413.GV185537@smile.fi.intel.com>
From:   Alper Nebi Yasak <alpernebiyasak@gmail.com>
Message-ID: <f332a19b-e8d1-d2b0-37c8-08381563f41b@gmail.com>
Date:   Thu, 30 Apr 2020 22:32:04 +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: <20200430164413.GV185537@smile.fi.intel.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 30/04/2020 19:44, Andy Shevchenko wrote:
> First of all I see only cover letter and one out of 3 patches.

Apologies, the tool I've used to send the patches (U-Boot's patman)
Cc-ed the scripts/get_maintainer.pl output per-patch, instead of
per-series as I had assumed it would. This was the first time I tried
it, I'll keep that in mind.

Here are links to all four emails:

https://lore.kernel.org/linux-serial/20200430161438.17640-1-alpernebiyasak@gmail.com/
https://lore.kernel.org/linux-serial/20200430161438.17640-2-alpernebiyasak@gmail.com/
https://lore.kernel.org/linux-serial/20200430161438.17640-3-alpernebiyasak@gmail.com/
https://lore.kernel.org/linux-serial/20200430161438.17640-4-alpernebiyasak@gmail.com/

Or I can resend the last two patches to you, or resend all the parts to
everyone again.

>> eventually figured out that the kernel preferred the serial port
>> (inaccessible to me) over the built-in working display/keyboard and was
>> probably asking there.
> 
> "probably". Please, confirm that first.
> Also, without command line it's hard to say what you have asked kernel to do.

I was trying to boot a Debian userspace with cryptsetup, with the kernel
command line:

	root=/dev/mapper/sda3_crypt quiet splash

The Debian initramfs handles most of the work (the password prompt,
device mounts, etc.).

When I used the same kernel/initramfs/rootfs on a QEMU aarch64 VM, it
only prompted on the serial console instead the framebuffer. I'm
assuming the same thing happens on my hardware as well.

I can also ask the Debian initramfs to launch a shell by adding "break"
to the command line, which won't be printed on my device's screen unless
I also add "console=tty0". That shell also only appears on the serial
console on the QEMU aarch64 VM, unless I again add "console=tty0".

This is my primary computer and I'd prefer not dismantling it, so my
findings above are the best I believe I can do to confirm it now. I'm 
hoping other people would be interested in this, and would test more 
than I can.

>> Running plymouth in the initramfs solves that specific problem, but
> 
> What is plymouth?

Plymouth is a userspace program that's famous for showing a splash
animation during boot, but in this context: it handles user-interaction
that might need to happen while the initramfs is running, by printing
messages and prompts and reading user input to/from all consoles.

>>    ------------------+-----------------------+-----------------------+
>>    Chromebook Plus   | tty0     -WU (EC p  ) | tty0     -WU (EC p  ) |
>>    (w/o either)      |                       |                       |
>>    ------------------+-----------------------+-----------------------+
> 
> either == SPCR or stdout-path?

As in "When the device has no SPCR _and_ no chosen stdout-path".

>> This patchset tries to ensure that VT is preferred in those conditions
>> even in the presence of firmware-mandated serial consoles.
> 
> This sounds completely wrong. serial should be preferred over vt due to very
> debugging on early stages and SPCR is exactly for that.

I'm saying that from a userspace perspective, and the patches explicitly
try to switch to the vt only after a real framebuffer is initialized. So
if I did it right, it would still use SPCR/stdout-path's console during
the early stages. (I admit I haven't adjusted to talking within a kernel 
context yet).

In all honesty, I'm not sure if this is even considered a kernel bug,
let alone my patches a correct solution; hence the RFC PATCH as an
attempt at demonstrating this can be "fixed" in kernel.

> Maybe you should figure out the real root cause?

Thanks for the reply. Any ideas on what else could be causing this 
behaviour?