linux-kernel - [RFC 0/1] serdes: Add whitelist to bring back missing serial port

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Date:   Mon, 16 Dec 2019 13:08:24 +0900
From:   Punit Agrawal <punit1.agrawal@...hiba.co.jp>
To:     linux-serial@...r.kernel.org
Cc:     Punit Agrawal <punit1.agrawal@...hiba.co.jp>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        nobuhiro1.iwamatsu@...hiba.co.jp, shrirang.bagul@...onical.com,
        robh@...nel.org, gregkh@...uxfoundation.org, johan@...nel.org,
        hdegoede@...hat.com
Subject: [RFC  0/1] serdes: Add whitelist to bring back missing serial port

Hi,

While booting v5.5-rc1 on Apollo Lake based UP2[0], I ran into an
issue with the primary serial port. The kernel is able to output to
ttyS0 but systemd isn't able to raise a login prompt. On further
investigation, it turns out that no serial device (/dev/ttyS0) is
being created as the device is claimed by serdev sub-system.

The issue has been reported in a few different places[0][1]. A patch
was proposed to solve the issue but there doesn't seem to be any
further progress[2]. Feedback on the thread suggested implementing a
whitelist based approach - which is what this RFC does.

With this patch, systemd is able to create a login prompt. The
whitelist has intentionally been left blank as it's not clear which
devices go in there.

Feedback welcome.

Thanks,
Punit

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=911831
[1] https://bugs.launchpad.net/ubuntu/+source/linux-oem/+bug/1769610
[2] https://marc.info/?l=linux-serial&m=152455861101408&w=2

Punit Agrawal (1):
  serdev: Only claim supported devices

 drivers/tty/serdev/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

-- 
2.24.0