linux-kernel - [PATCH v7 7/7] Documentation: kernel-parameters: Add DEVNAME:0.0 format for serial ports

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Message-ID: <20240327110021.59793-8-tony@atomide.com>
Date: Wed, 27 Mar 2024 12:59:41 +0200
From: Tony Lindgren <tony@...mide.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: "David S . Miller" <davem@...emloft.net>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Dhruva Gole <d-gole@...com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Johan Hovold <johan@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Vignesh Raghavendra <vigneshr@...com>,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	Sebastian Reichel <sre@...nel.org>,
	linux-doc@...r.kernel.org
Subject: [PATCH v7 7/7] Documentation: kernel-parameters: Add DEVNAME:0.0 format for serial ports

Document the console option for DEVNAME:0.0 style addressing for serial
ports.

Suggested-by: Sebastian Reichel <sre@...nel.org>
Signed-off-by: Tony Lindgren <tony@...mide.com>
---
 .../admin-guide/kernel-parameters.txt         | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -785,6 +785,25 @@
 			Documentation/networking/netconsole.rst for an
 			alternative.
 
+		<DEVNAME>:<n>.<n>[,options]
+			Use the specified serial port on the serial core bus.
+			The addressing uses DEVNAME of the physical serial port
+			device, followed by the serial core controller instance,
+			and the serial port instance. The options are the same
+			as documented for the ttyS addressing above.
+
+			The mapping of the serial ports to the tty instances
+			can be viewed with:
+
+			$ ls -d /sys/bus/serial-base/devices/*:*.*/tty/*
+			/sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0
+
+			In the above example, the console can be addressed with
+			console=00:04:0.0. Note that a console addressed this
+			way will only get added when the related device driver
+			is ready. The use of an earlycon parameter in addition to
+			the console may be desired for console output early on.
+
 		uart[8250],io,<addr>[,options]
 		uart[8250],mmio,<addr>[,options]
 		uart[8250],mmio16,<addr>[,options]
-- 
2.44.0