linux-kernel - [PATCH v2 0/3] Handle NBCON consoles on KDB

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Message-Id: <20250811-nbcon-kgdboc-v2-0-c7c72bcdeaf6@suse.com>
Date: Mon, 11 Aug 2025 10:32:44 -0300
From: Marcos Paulo de Souza <mpdesouza@...e.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
 John Ogness <john.ogness@...utronix.de>, 
 Sergey Senozhatsky <senozhatsky@...omium.org>, 
 Jason Wessel <jason.wessel@...driver.com>, 
 Daniel Thompson <danielt@...nel.org>, 
 Douglas Anderson <dianders@...omium.org>
Cc: linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net, 
 Marcos Paulo de Souza <mpdesouza@...e.com>
Subject: [PATCH v2 0/3] Handle NBCON consoles on KDB

After the proposed patches [1], it was suggested to start using
console_is_usable instead of checking if a console is enabled. It was
noticed that KDB was always calling con->write method, but this
callback is not set for NBCON consoles.

To fix this usecase, export console_is_usable and add new nbcon code to
acquire a context that KDB needs in order to call ->write_atomic. After
these patches are accepted I'm planning to go back to [1] again to use
the function expected here.

I did the tests using qemu and reapplying commit f79b163c4231
('Revert "serial: 8250: Switch to nbcon console"') created originally by
John, just to exercise the common 8250 serial from qemu. The commit can
be checked on [2]. I had to solve some conflicts since the code has been
reworked after the commit was reverted.

Without these patches, NBCON consoles won't receive the kgdb messages. I
tested using [2], and it works after this patchset.

Thanks to all reviewers of the patches posted on [1]! I hope this is the
first step into implementing all the changes suggested in that patchset.

[1]: https://lore.kernel.org/lkml/20250606-printk-cleanup-part2-v1-0-f427c743dda0@suse.com/
[2]: https://github.com/marcosps/linux/commit/bea249773c9caf56821f9ec06c7f9649e4966c61

Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>
---
Changes in v2:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v1: https://lore.kernel.org/r/20250713-nbcon-kgdboc-v1-0-51eccd9247a8@suse.com

---
Marcos Paulo de Souza (3):
      printk: nbcon: Export console_is_usable
      printk: nbcon: Introduce KDB helpers
      kdb: Adapt kdb_msg_write to work with NBCON consoles

 include/linux/console.h   | 50 +++++++++++++++++++++++++++++++++++++++++++++++
 kernel/debug/kdb/kdb_io.c | 26 ++++++++++++++++++++----
 kernel/printk/internal.h  | 41 --------------------------------------
 kernel/printk/nbcon.c     | 26 ++++++++++++++++++++++++
 4 files changed, 98 insertions(+), 45 deletions(-)
---
base-commit: bea249773c9caf56821f9ec06c7f9649e4966c61
change-id: 20250713-nbcon-kgdboc-efcfc37fde46

Best regards,
-- 
Marcos Paulo de Souza <mpdesouza@...e.com>