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>

1 files changed, 15 insertions, 3 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bfcb1a62a7b4..1facf0bebb31 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