linux-kernel - [PATCH] earlycon: 8250: Document kernel command line options

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Message-Id: <1428331959-21865-1-git-send-email-peter@hurleysoftware.com>
Date:	Mon,  6 Apr 2015 10:52:39 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH] earlycon: 8250: Document kernel command line options

Document the expected behavior of kernel command lines of the forms:
    console=uart[8250],io|mmio|mmio32,<addr>[,options]
    console=uart[8250],<addr>[,options]
and
    earlycon=uart[8250],io|mmio|mmio32,<addr>[,options]
    earlycon=uart[8250],<addr>[,options]

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 Documentation/kernel-parameters.txt | 18 +++++++++++++++---
 drivers/tty/serial/8250/8250_core.c |  5 +++--
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bfcb1a6..1facf0b 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -713,10 +713,18 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 		uart[8250],io,<addr>[,options]
 		uart[8250],mmio,<addr>[,options]
+		uart[8250],mmio32,<addr>[,options]
+		uart[8250],0x<addr>[,options]
 			Start an early, polled-mode console on the 8250/16550
 			UART at the specified I/O port or MMIO address,
-			switching to the matching ttyS device later.  The
-			options are the same as for ttyS, above.
+			switching to the matching ttyS device later.
+			MMIO inter-register address stride is either 8-bit
+			(mmio) or 32-bit (mmio32).
+			If none of [io|mmio|mmio32], <addr> is assumed to be
+			equivalent to 'mmio'. 'options' are specified in the
+			same format described for ttyS above; if unspecified,
+			the h/w is not re-initialized.
+
 		hvc<n>	Use the hypervisor console device <n>. This is for
 			both Xen and PowerPC hypervisors.
 
@@ -944,11 +952,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 		uart[8250],io,<addr>[,options]
 		uart[8250],mmio,<addr>[,options]
 		uart[8250],mmio32,<addr>[,options]
+		uart[8250],0x<addr>[,options]
 			Start an early, polled-mode console on the 8250/16550
 			UART at the specified I/O port or MMIO address.
 			MMIO inter-register address stride is either 8-bit
 			(mmio) or 32-bit (mmio32).
-			The options are the same as for ttyS, above.
+			If none of [io|mmio|mmio32], <addr> is assumed to be
+			equivalent to 'mmio'. 'options' are specified in the
+			same format described for "console=ttyS<n>"; if
+			unspecified, the h/w is not initialized.
 
 		pl011,<addr>
 			Start an early, polled-mode console on a pl011 serial
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 18142ee..422ebea 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -3471,12 +3471,13 @@ static int univ8250_console_setup(struct console *co, char *options)
  *	@options: ptr to option string from console command line
  *
  *	Only attempts to match console command lines of the form:
- *	    console=uart<>,io|mmio|mmio32,<addr>,<options>
- *	    console=uart<>,<addr>,options
+ *	    console=uart[8250],io|mmio|mmio32,<addr>[,<options>]
+ *	    console=uart[8250],0x<addr>[,<options>]
  *	This form is used to register an initial earlycon boot console and
  *	replace it with the serial8250_console at 8250 driver init.
  *
  *	Performs console setup for a match (as required by interface)
+ *	If no <options> are specified, then assume the h/w is already setup.
  *
  *	Returns 0 if console matches; otherwise non-zero to use default matching
  */
-- 
2.3.5

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