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From: Alper Nebi Yasak <alpernebiyasak@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>, Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: linux-serial@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	Alper Nebi Yasak <alpernebiyasak@gmail.com>,
	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>,
	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>
Subject: [RFC PATCH v2 0/3] Prefer working VT console over SPCR and device-tree chosen stdout-path
Date: Thu, 30 Apr 2020 19:14:34 +0300	[thread overview]
Message-ID: <20200430161438.17640-1-alpernebiyasak@gmail.com> (raw)

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.

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.

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)      |                       |                       |
  ------------------+-----------------------+-----------------------+

This patchset tries to ensure that VT is preferred in those conditions
even in the presence of firmware-mandated serial consoles. 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]

[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

Changes in v2:
- Fix #elif to #else (Reported-by: kbuild test robot <lkp@intel.com>)
- Refresh dmesg outputs with/without earlycon for next-20200430
- Use the correct format when referencing a commit

Alper Nebi Yasak (3):
  printk: Add function to set console to preferred console's driver
  vt: Set as preferred console when a non-dummy backend is bound
  printk: Preset tty0 as a pseudo-preferred console

 drivers/tty/vt/vt.c     |  7 +++++
 include/linux/console.h |  1 +
 kernel/printk/printk.c  | 68 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+)

-- 
2.26.2


             reply	other threads:[~2020-04-30 16:16 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-30 16:14 Alper Nebi Yasak [this message]
2020-04-30 16:14 ` [RFC PATCH v2 1/3] printk: Add function to set console to preferred console's driver Alper Nebi Yasak
2020-04-30 16:46   ` Andy Shevchenko
2020-05-01  1:44   ` Sergey Senozhatsky
2020-05-01 11:48     ` Alper Nebi Yasak
2020-05-13  5:35   ` Sergey Senozhatsky
2020-05-24 10:01     ` Daniel Vetter
2020-04-30 16:14 ` [RFC PATCH v2 2/3] vt: Set as preferred console when a non-dummy backend is bound Alper Nebi Yasak
2020-04-30 16:14 ` [RFC PATCH v2 3/3] printk: Preset tty0 as a pseudo-preferred console Alper Nebi Yasak
2020-04-30 16:44 ` [RFC PATCH v2 0/3] Prefer working VT console over SPCR and device-tree chosen stdout-path Andy Shevchenko
2020-04-30 19:32   ` Alper Nebi Yasak
2020-05-01  1:30 ` Sergey Senozhatsky
2020-05-01 11:08   ` Alper Nebi Yasak
2020-05-01 13:16     ` Andy Shevchenko
2020-05-01 15:07       ` Alper Nebi Yasak
2020-05-13 14:37 ` Petr Mladek
2020-05-13 22:22   ` Benjamin Herrenschmidt
2020-05-15 19:27   ` Alper Nebi Yasak
2020-05-25 13:04     ` Petr Mladek

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