linux-kernel - Re: RE: [PATCH] printk: nbcon: check uart port is nbcon or not in nbcon

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Date: Wed, 17 Jan 2024 11:24:46 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: John Ogness <john.ogness@...utronix.de>
Cc: "Chang, Junxiao" <junxiao.chang@...el.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Li, Hao3" <hao3.li@...el.com>, "Li, Lili" <lili.li@...el.com>,
	"Gao, Jianfeng" <jianfeng.gao@...el.com>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>
Subject: Re: RE: [PATCH] printk: nbcon: check uart port is nbcon or not in
 nbcon_release

On 2024-01-17 11:09:24 [+0106], John Ogness wrote:
> On 2024-01-17, "Chang, Junxiao" <junxiao.chang@...el.com> wrote:
> > There are several serial ports in one Intel ADL hardware, they are
> > enumerated as ttyS0, ttyS1, ttyS4, and so on. Multiple console options
> > might be appended to kernel command line. For example,
> > "console=ttyS0,115200n8 console=ttyS4,115200n8
> > console=ttyS5,115200n8".
> >
> > In this case, several uarts "cons" pointers are same.
> 
> So I ask again. Please explain how this is possible.

I have here
| 00:03: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
| 00:04: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A

and I have

| root        2315  0.0  0.0   5480  1792 ttyS0    Ss+  11:19   0:00 /sbin/agetty -o -p -- \u --keep-baud 115200,57600,38400,9600 - vt220
| root        2502  0.1  0.0   5480  1792 ttyS1    Ss+  11:20   0:00 /sbin/agetty -o -p -- \u --keep-baud 115200,57600,38400,9600 - vt220

and I can stop both of them without any trouble. 
Can this be reproduced on an ordinary x86 hardware given they have more
than one UART (up to four).
Is any of this ADL hardware upstream?

> John

Sebastian