linux-kernel - Re: [BUG] Suspend failure with nbcon + pm_debug

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Message-ID: <87tszamcaz.fsf@jogness.linutronix.de>
Date: Tue, 04 Nov 2025 09:34:36 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Sherry Sun <sherry.sun@....com>, "esben@...nix.com" <esben@...nix.com>,
 "pmladek@...e.com" <pmladek@...e.com>, "senozhatsky@...omium.org"
 <senozhatsky@...omium.org>, "tglx@...utronix.de" <tglx@...utronix.de>,
 Greg KH <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>,
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 "ryotkkr98@...il.com" <ryotkkr98@...il.com>, "kkartik@...dia.com"
 <kkartik@...dia.com>, "fj6611ie@...jp.fujitsu.com"
 <fj6611ie@...jp.fujitsu.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-serial
 <linux-serial@...r.kernel.org>, "imx@...ts.linux.dev"
 <imx@...ts.linux.dev>, Pengutronix Kernel Team <kernel@...gutronix.de>,
 "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [BUG] Suspend failure with nbcon + pm_debug_messages (Linux
 6.18-rc4)

Hi Sherry,

On 2025-11-04, Sherry Sun <sherry.sun@....com> wrote:
> Since the latest i.MX UART switch to nbcon console with commit
> 70acca67bdd3 ("serial: imx: Switch to nbcon console"), I'm
> encountering a suspend issue on an i.MX8MP EVK board while testing
> with Linux 6.18-rc4.
>
> The system fails to suspend when both nbcon is enabled and
> `pm_debug_messages` is turned on. When `pm_debug_messages` is
> disabled, suspend works normally. Additionally, if I revert the patch
> that adds nbcon support for the i.MX UART, suspend also works fine
> even with `pm_debug_messages` enabled.

Thanks for reporting! I believe this is the same issue reported by
NVIDIA [0] when we tried to switch the 8250 UART driver to nbcon.

We have been working with NVIDIA recently to address the issue. There is
a patch [1] we are currently testing that looks good so far. It is based
on 6.17 but should work fine for 6.18-rc4 as well. Can you give it a
spin?

John Ogness

[0] https://lore.kernel.org/lkml/80b020fc-c18a-4da4-b222-16da1cab2f4c@nvidia.com

[1] https://github.com/Linutronix/linux/commit/ae173249d9028ef159fba040bdab260d80dda43f