linux-kernel - Re: [RFC/PATCH] printk: Fix preferred console selection with multiple matches

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Date:   Tue, 10 Dec 2019 17:01:54 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        AlekseyMakarov <aleksey.makarov@...aro.org>
Subject: Re: [RFC/PATCH] printk: Fix preferred console selection with
 multiple matches

On (19/12/10 11:57), Benjamin Herrenschmidt wrote:
[..]
>  - add_preferred_console is called early to register "uart0". In
> our case that happens from acpi_parse_spcr() on arm64 since the
> "enable_console" argument is true on that architecture. This causes
> "uart0" to become entry 0 of the console_cmdline array.

Hmm, two independent console list configuration sources.

[..]
> +++ b/kernel/printk/printk.c
> @@ -2646,8 +2646,8 @@ void register_console(struct console *newcon)
>  		if (i == preferred_console) {
>  			newcon->flags |= CON_CONSDEV;
>  			has_preferred = true;
> +			break;
>  		}
> -		break;
>  	}
>  
>  	if (!(newcon->flags & CON_ENABLED))

Wouldn't this, basically, mean that we want to match only consoles,
which were in the kernel's console= cmdline? IOW, ignore consoles
that were placed into consoles list via alternative path - ACPI.

Hmm.

The patch may affect setups where alias matching is expected to
happen. E.g.:

	console=uartFOO,BAR

Is 8250 the only console that does alias matching?

	-ss