linux-kernel - Re: [PATCH v6 0/5] Handle NBCON consoles on KDB

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Message-ID: <aPtodUgB37thKUMb@pathway.suse.cz>
Date: Fri, 24 Oct 2025 13:52:21 +0200
From: Petr Mladek <pmladek@...e.com>
To: Marcos Paulo de Souza <mpdesouza@...e.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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>,
	linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net
Subject: Re: [PATCH v6 0/5] Handle NBCON consoles on KDB

On Thu 2025-10-16 11:47:53, Marcos Paulo de Souza wrote:
> In v6 the patches were rebased on top of v6.18-rc1, added Reviewed-by tags from
> John and did some small changes suggested by him as well.
> 
> As usual, how I tested the changes:
> 
> Testing
> -------
> 
> 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 [1]. I had to solve some conflicts since the code has been
> reworked after the commit was reverted.
> 
> Then I would create three different serial entries on qemu:
> -serial mon:stdio -serial pty -serial pty
> 
> And for the kernel command line I added:
> earlyprintk=serial,ttyS2 console=ttyS2 console=ttyS1 console=ttyS1 kgdboc=ttyS1,115200
> 
> Without the last patch on this patchset, when KDB is triggered, the mirroring
> only worked on the earlyprintk console, since it's using the legacy console.
> 
> With the last patch applied, KDB mirroring works on legacy and nbcon
> console. For debugging I added some messages to be printed by KDB, showing
> also the console->name and console->index, and I was able to see both
> ->write and ->write_atomic being called, and it all working together.
> 
> [1]: https://github.com/marcosps/linux/commit/618bd49f8533db85d9c322f9ad1cb0da22aca9ee
> [2]: https://lore.kernel.org/lkml/20250825022947.1596226-1-wangjinchao600@gmail.com/
> 
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>
> ---
> Changes in v6:
> - Rebased on top opf v6.18-rc1
> - Changed some includes, as suggedted by John
> - Reworked comments as suggested by John

> Marcos Paulo de Souza (5):
>       printk: nbcon: Export console_is_usable
>       printk: nbcon: Introduce KDB helpers
>       printk: nbcon: Allow KDB to acquire the NBCON context
>       printk: nbcon: Export nbcon_write_context_set_buf
>       kdb: Adapt kdb_msg_write to work with NBCON consoles
> 
>  include/linux/console.h   | 55 ++++++++++++++++++++++++++++++++++++
>  include/linux/kdb.h       | 16 +++++++++++
>  kernel/debug/kdb/kdb_io.c | 47 +++++++++++++++++++++----------
>  kernel/printk/internal.h  | 45 ------------------------------
>  kernel/printk/nbcon.c     | 71 +++++++++++++++++++++++++++++++++++++++++++++--
>  5 files changed, 171 insertions(+), 63 deletions(-)

JFYI, the patchset has been committed into printk/linux.git,
branch rework/nbcon-in-kdb.

Note: As promised, I have fixed the two compilation problems reported
      by the robots when committing.

Best Regards,
Petr