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, 30 Apr 2020 19:44:13 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Alper Nebi Yasak <alpernebiyasak@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Petr Mladek <pmladek@...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>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        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 Thu, Apr 30, 2020 at 07:14:34PM +0300, Alper Nebi Yasak wrote:

First of all I see only cover letter and one out of 3 patches.

> I recently experienced some trouble with setting up an encrypted-root
> system, my Chromebook Plus (rk3399-gru-kevin, ARM64) would appear to
> hang where it should have asked for an encryption passphrase; and I
> 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.

> Running plymouth in the initramfs solves that specific problem, but
> both the documentation and tty-related kconfig descriptions imply that
> /dev/console should be tty0 if graphics are working, CONFIG_VT_CONSOLE
> is enabled and no explicit console argument is given in the kernel
> commandline.

What is plymouth?

> However, I'm seeing different behaviour on systems with SPCR (as in QEMU
> aarch64 virtual machines) and/or a device-tree chosen stdout-path node
> (as in most arm/arm64 devices). On these machines, depending on the
> console argument, the contents of the /proc/consoles file are:
> 
>                     |     "console=tty0"    |    (no console arg)   |
>   ------------------+-----------------------+-----------------------+
>   QEMU VM           | tty0     -WU (EC p  ) | ttyAMA0  -W- (EC   a) |
>   (w/ SPCR)         | ttyAMA0  -W- (E    a) |                       |
>   ------------------+-----------------------+-----------------------+
>   Chromebook Plus   | tty0     -WU (EC p  ) | ttyS2    -W- (EC p a) |
>   (w/ stdout-path)  |                       | tty0     -WU (E     ) |
>   ------------------+-----------------------+-----------------------+
>   Chromebook Plus   | tty0     -WU (EC p  ) | tty0     -WU (EC p  ) |
>   (w/o either)      |                       |                       |
>   ------------------+-----------------------+-----------------------+

either == SPCR or 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.

> These should
> cleanly apply onto next-20200430.
> 
> More discussion due to or about the console confusion on ARM64:
> - My Debian bug report about the initramfs prompts [0]
> - Fedora test issue arising from ARM64 QEMU machines having SPCR [1]
> - Debian-installer discussion on what to do with multiple consoles [2]

Maybe you should figure out the real root cause?

> [0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=952452
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1661288
> [2] https://lists.debian.org/debian-boot/2019/01/msg00184.html

-- 
With Best Regards,
Andy Shevchenko