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[3/3] Documentation: kernel-parameters: Add DEVNAME:0.0 format for serial ports

Message ID 20240703100615.118762-4-tony.lindgren@linux.intel.com
State New
Headers show
Series [1/3] printk: Add match_devname_and_update_preferred_console() | expand

Commit Message

Tony Lindgren July 3, 2024, 10:06 a.m. UTC 
From: Tony Lindgren <tony@atomide.com>

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

Suggested-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
---
 .../admin-guide/kernel-parameters.txt         | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
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Patch

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 27ec49af1bf2..11e57ba2985c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -788,6 +788,25 @@ 
 			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]