linux-kernel - Re: [PATCH 6/6] serial: 8250_dw: Ensure BUSY is deasserted

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Message-ID: <871pjb6nb7.fsf@jogness.linutronix.de>
Date: Tue, 27 Jan 2026 17:25:08 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Ilpo Järvinen
 <ilpo.jarvinen@...ux.intel.com>, Petr Mladek <pmladek@...e.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby
 <jirislaby@...nel.org>, linux-serial <linux-serial@...r.kernel.org>,
 qianfan Zhao <qianfanguijin@....com>, Adriana Nicolae
 <adriana@...sta.com>, Markus Mayer <markus.mayer@...aro.org>, Tim Kryger
 <tim.kryger@...aro.org>, Matt Porter <matt.porter@...aro.org>, Heikki
 Krogerus <heikki.krogerus@...ux.intel.com>, Jamie Iles
 <jamie@...ieiles.com>, LKML <linux-kernel@...r.kernel.org>,
 stable@...r.kernel.org, "Bandal, Shankar" <shankar.bandal@...el.com>,
 "Murthy, Shanth" <shanth.murthy@...el.com>
Subject: Re: [PATCH 6/6] serial: 8250_dw: Ensure BUSY is deasserted

On 2026-01-27, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
>> > > +	if (d->in_idle) {
>> > 
>> > > +		/*
>> > > +		 * FIXME: this deadlocks if port->lock is already held
>> > > +		 * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
>> > > +		 */
>> > 
>> > Hmm... That FIXME should gone since we have non-blocking consoles, no?
>> 
>> No, lockdep still gets angry if printing is used while holding port's 
>> lock.
>
> Hmm... Let's ask PRINTK people about this. John, do we still have a gap
> with nbcon? Or did I misunderstand the scope of its use?

The 8250 has not yet been converted to a nbcon. I am still working on
it. Unfortunately I got side-tracked first fixing the broken 8250
console hardware-flow-control support. :-/

So the comment is correct. Once the driver converts to nbcon, the
dev_err() is fine.

Note that if the message is important, you could use a printk_deferred()
here with a FIXME to say to convert it to dev_err() once the 8250
supports nbcon.

John Ogness