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@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bfcb1a62a7b48466f3cbe5a08d3e1a632eadc3d2..1facf0bebb31df9c2976475be135c8a675489fb9 100644 (file)
--- 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 18142ee3c0130b8fcee8427306bd8f42170c79e5..422ebea96a64ae01d473266c214db4b66fb7a5ec 100644 (file)
--- 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
  */