linux-kernel - Re: [PATCH printk v3 23/40] serial_core: replace uart_console_enabled() with uart_console

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Date:   Thu, 10 Nov 2022 14:24:36 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Tony Lindgren <tony@...mide.com>,
        Lukas Wunner <lukas@...ner.de>, linux-serial@...r.kernel.org
Subject: Re: [PATCH printk v3 23/40] serial_core: replace
 uart_console_enabled() with uart_console_registered()

On Tue 2022-11-08 09:46:20, Geert Uytterhoeven wrote:
> Hi John,
> 
> On Mon, Nov 7, 2022 at 3:16 PM John Ogness <john.ogness@...utronix.de> wrote:
> > All users of uart_console_enabled() really want to know if a console
> > is registered. It is not reliable to check for CON_ENABLED in order
> > to identify if a console is registered. Use console_is_registered()
> > instead.
> >
> > A _locked() variant is provided because uart_set_options() is always
> > called with the console_list_lock held and must check if a console
> > is registered in order to synchronize with kgdboc.
> >
> > Signed-off-by: John Ogness <john.ogness@...utronix.de>
> 
> > --- a/include/linux/serial_core.h
> > +++ b/include/linux/serial_core.h
> > @@ -743,9 +743,20 @@ static const bool earlycon_acpi_spcr_enable EARLYCON_USED_OR_UNUSED;
> >  static inline int setup_earlycon(char *buf) { return 0; }
> >  #endif
> >
> > -static inline bool uart_console_enabled(struct uart_port *port)
> > +/* Variant of uart_console_registered() when the console_list_lock is held. */
> > +static inline bool uart_console_registered_locked(struct uart_port *port)
> >  {
> > -       return uart_console(port) && (port->cons->flags & CON_ENABLED);
> > +       return uart_console(port) && console_is_registered_locked(port->cons);
> > +}
> > +
> > +static inline bool uart_console_registered(struct uart_port *port)
> > +{
> > +       bool ret;
> > +
> > +       console_list_lock();
> > +       ret = uart_console_registered_locked(port);
> > +       console_list_unlock();
> > +       return ret;
> 
> Perhaps
> 
>     return uart_console(port) && console_is_registered();
> 
> to avoid locking the list when the first condition is not true?

I do not have strong opinion on this. It is true that the code
duplication is trivial but it is a code duplication. Either
way would work for me.

The reset of the code looks good. Feel free to use:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr