linux-kernel - Re: [PATCH] ARM: early_printk: respect keep parameter

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Date:   Tue, 17 Jul 2018 16:16:44 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
cc:     Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: early_printk: respect keep parameter

On Wed, 11 Jul 2018, Alexandre Belloni wrote:

> Parse and use the keep parameter of earlyprintk to avoid having the kernel
> output stop with:
> 
> Console: colour dummy device 80x30
> console [tty0] enabled
> bootconsole [earlycon0] disabled
> 
> This happens because once tty0, the virtual terminal console is registered,
> it is selected as the default console, disregarding an existing stdout-path
> DT property and the early console is shutdown before the console driver is
> probed.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>

Why can't you have a real console driver that takes over at that point 
which respects whatever DT property you give it?

The early_printk code is very raw and inefficient, and it shouldn't be 
used for anything but the debugging of early boot hangs.

> ---
>  arch/arm/kernel/early_printk.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/kernel/early_printk.c b/arch/arm/kernel/early_printk.c
> index 9257736ec9fa..bbb10150b11a 100644
> --- a/arch/arm/kernel/early_printk.c
> +++ b/arch/arm/kernel/early_printk.c
> @@ -42,6 +42,9 @@ static struct console early_console_dev = {
>  
>  static int __init setup_early_printk(char *buf)
>  {
> +	if (buf && strstr(buf, "keep"))
> +		early_console_dev.flags &= ~CON_BOOT;
> +
>  	early_console = &early_console_dev;
>  	register_console(&early_console_dev);
>  	return 0;
> -- 
> 2.18.0
> 
>