linux-kernel - Re: [PATCH tty-next v1 0/2] convert 8250 to nbcon

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Message-ID: <Ztm36qPI7fVteSX_@smile.fi.intel.com>
Date: Thu, 5 Sep 2024 16:53:46 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>, Petr Mladek <pmladek@...e.com>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Serge Semin <fancer.lancer@...il.com>,
	Rengarajan S <rengarajan.s@...rochip.com>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	Lino Sanfilippo <l.sanfilippo@...bus.com>,
	Derek Barbosa <debarbos@...hat.com>
Subject: Re: [PATCH tty-next v1 0/2] convert 8250 to nbcon

On Thu, Sep 05, 2024 at 03:53:17PM +0206, John Ogness wrote:
> The recent printk rework introduced a new type of console NBCON
> that will perform printing via a dedicated kthread during
> normal operation. For times when the kthread is not available
> (early boot, panic, reboot/shutdown) the NBCON console will
> print directly from the printk() calling context (even if from
> NMI).
> 
> Futher details about NBCON consoles are available here [0].
> 
> This series converts the 8250 driver to an NBCON console,
> providing both threaded and atomic printing implementations.
> Users can verify the UART console is an NBCON console via the
> proc filesystem. For example:
> 
> $  cat /proc/consoles
> ttyS0                -W- (EC N  a)    4:64
> 
> The 'N' shows that it is an NBCON console.
> 
> There will also be a dedicated printing kthread. For example:
> 
> $ ps ax | grep pr/
>    16 root       0:00 [pr/ttyS0]

Wondering if this can use the DEVNAME instead of opaque (to some extent) ttySx?
Or is it using the same what has been passed to the console= kernel command line
parameter?

> Derek Barbosa performed extensive tests [1] using this driver
> and encountered no issues. On the contrary, his tests showed
> the improved reliability and non-interference features of the
> NBCON-based driver.
> 
> Since this is the first console driver to be converted to an
> NBCON console, it may include variables and functions that
> could be abstracted to all UART consoles (such as the
> @console_newline_needed field). However, we can abstract such
> things later as more consoles are converted to NBCON.
> 
> John Ogness
> 
> [0] https://lore.kernel.org/lkml/20230302195618.156940-1-john.ogness@linutronix.de
> [1] https://lore.kernel.org/lkml/ZsdoD6PomBRsB-ow@debarbos-thinkpadt14sgen2i.remote.csb

-- 
With Best Regards,
Andy Shevchenko