linux-kernel - Re: [PATCH tty-next v4 0/6] convert 8250 to nbcon

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Message-ID: <841pxpqvua.fsf@jogness.linutronix.de>
Date: Mon, 30 Dec 2024 12:06:29 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby
 <jirislaby@...nel.org>, Petr Mladek <pmladek@...e.com>, Sergey Senozhatsky
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 linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org, Arnd Bergmann
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 linux-rpi-kernel@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH tty-next v4 0/6] convert 8250 to nbcon

On 2024-12-29, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> On Fri, Dec 27, 2024 at 11:51:16PM +0106, John Ogness wrote:
>> This is v4 of a series to convert the 8250 driver to an NBCON
>> console, providing both threaded and atomic printing
>> implementations. v3 of this series is here [0]. Additional
>> background information about NBCON consoles in general is
>> available in the cover letter of v2 [1].
>
> Just to be sure I understand the side effect of this series, i.e.
> the
>
> https://elixir.bootlin.com/linux/v6.13-rc3/source/drivers/tty/serial/8250/8250_port.c#L44
> https://elixir.bootlin.com/linux/v6.13-rc3/source/drivers/tty/serial/8250/8250_pci.c#L9
>
> are not needed anymore (the first one can be replaced to something like
> dev_dbg() or analogue)?

Correct. With NBCON console drivers it is safe to call printk() while
holding the port lock for non-console-printing purposes because:

1. printing via ->write_atomic() does not use the port lock

   and

2. printing via ->write_thread() is performed in a separate dedicated
   printing kthread that can safely spin on the port lock

John