linux-kernel - Re: [PATCH printk v3 40/40] tty: serial: sh-sci: use setup() callback for early console

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Date:   Tue, 8 Nov 2022 09:53:29 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        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>,
        linux-serial@...r.kernel.org,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH printk v3 40/40] tty: serial: sh-sci: use setup() callback
 for early console

Hi John,

CC linux-sh (SH-specific code)
CC linux-renesas-soc (JFYI)

On Mon, Nov 7, 2022 at 3:20 PM John Ogness <john.ogness@...utronix.de> wrote:
> When setting up the early console, the setup() callback of the
> regular console is used. It is called manually before registering
> the early console instead of providing a setup() callback for the
> early console. This is probably because the early setup needs a
> different @options during the early stage.
>
> The issue here is that the setup() callback is called without the
> console_list_lock held and functions such as uart_set_options()
> expect that.
>
> Rather than manually calling the setup() function before registering,
> provide an early console setup() callback that will use the different
> early options. This ensures that the error checking, ordering, and
> locking context when setting up the early console are correct.
>
> Note that technically the current implementation works because it is
> only used in early boot. And since the early console setup is
> performed before registering, it cannot race with anything and thus
> does not need any locking. However, longterm maintenance is easier
> when drivers rely on the subsystem API rather than manually
> implementing steps that could cause breakage in the future.
>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

Thanks for your patch!

> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -3054,15 +3054,26 @@ static struct console serial_console = {
>  };
>
>  #ifdef CONFIG_SUPERH
> +static char early_serial_buf[32];
> +
> +static int early_serial_console_setup(struct console *co, char *options)
> +{
> +       WARN_ON(options);
> +       /*
> +        * Use @early_serial_buf because @options will always be
> +        * NULL at this early stage.
> +        */
> +       return serial_console_setup(co, early_serial_buf);
> +}
> +
>  static struct console early_serial_console = {
>         .name           = "early_ttySC",
>         .write          = serial_console_write,
> +       .setup          = early_serial_console_setup,
>         .flags          = CON_PRINTBUFFER,
>         .index          = -1,
>  };
>
> -static char early_serial_buf[32];
> -
>  static int sci_probe_earlyprintk(struct platform_device *pdev)
>  {
>         const struct plat_sci_port *cfg = dev_get_platdata(&pdev->dev);
> @@ -3074,8 +3085,6 @@ static int sci_probe_earlyprintk(struct platform_device *pdev)
>
>         sci_init_single(pdev, &sci_ports[pdev->id], pdev->id, cfg, true);
>
> -       serial_console_setup(&early_serial_console, early_serial_buf);
> -
>         if (!strstr(early_serial_buf, "keep"))
>                 early_serial_console.flags |= CON_BOOT;
>
> --
> 2.30.2

LGTM, so
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds