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

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Message-ID: <3444595a705960b1f38a34368c22d637a92ffa4d.camel@suse.com>
Date: Tue, 12 Aug 2025 14:14:28 -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
Subject: Re: [PATCH v2 0/3] Handle NBCON consoles on KDB

On Mon, 2025-08-11 at 10:32 -0300, Marcos Paulo de Souza wrote:
> 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

This patchset wasn't thought as a v2 of [1], but somehow I messed up
with my b4 setup, and it's like this... ignore the v2 mark :)

> 
> ---
> 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,