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From:   John Ogness <john.ogness@linutronix.de>
To:     Ilpo =?utf-8?Q?J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        linux-serial <linux-serial@vger.kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Tony Lindgren <tony@atomide.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Florian Fainelli <f.fainelli@gmail.com>
Subject: Re: [PATCH tty v1 06/74] serial: 8250: Use port lock wrappers
In-Reply-To: <2045de5e-b7f8-18fe-dc92-e1d88a62f810@linux.intel.com>
References: <20230914183831.587273-1-john.ogness@linutronix.de>
 <20230914183831.587273-7-john.ogness@linutronix.de>
 <2045de5e-b7f8-18fe-dc92-e1d88a62f810@linux.intel.com>
Date:   Fri, 15 Sep 2023 13:27:05 +0206
Message-ID: <87y1h7vg0u.fsf@jogness.linutronix.de>
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On 2023-09-15, Ilpo J=C3=A4rvinen <ilpo.jarvinen@linux.intel.com> wrote:
>> @@ -3403,9 +3403,9 @@ void serial8250_console_write(struct uart_8250_por=
t *up, const char *s,
>>  	touch_nmi_watchdog();
>>=20=20
>>  	if (oops_in_progress)
>> -		locked =3D spin_trylock_irqsave(&port->lock, flags);
>> +		locked =3D uart_port_trylock_irqsave(port, &flags);
>>  	else
>> -		spin_lock_irqsave(&port->lock, flags);
>> +		uart_port_lock_irqsave(port, &flags);
>
> Not related to any problem (with this patch) but I'm a bit curious is
> this construct going to remain there after the follow-up work?

Yes. The uart port lock already provides excellent coverage of unsafe
regions in uart drivers. We want to take advantage of that.

> And there's the similar one in some other drivers (with some
> variations related to local_irq_save()):
>
>         if (port->sysrq) {
>                 locked =3D 0;
>         } else if (oops_in_progress) {
>                 locked =3D spin_trylock(&port->lock);
>         } else {
>                 spin_lock(&port->lock);
>                 locked =3D 1;
>         }

With the follow-up work we are introducing a new type of console
(CON_NBCON) that supports atomic and threaded printing. Current console
drivers must be converted if they want these features. When converting a
driver to NBCON, such variations as above will need to be addressed. The
follow-up work provides new functions and semantics to allow drivers to
implement more reliable code than just: "trylock and keep going no
matter what".

For console drivers that are _not_ converted to NBCON, the uart port
lock wrappers will not provide any changed functionality.

John Ogness