tty/serial: add arm/arm64 semihosting earlycon

Add earlycon support for the arm/arm64 semihosting debug serial
interface. This allows enabling a debug console when early_params are
processed. This is based on the arm64 earlyprintk smh support and is
intended to replace it.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 2609ead7ff55..4946d8e58d53 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -899,6 +899,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         must already be setup and configured. Options are not
                         yet supported.
 
+                smh     Use ARM semihosting calls for early console.
+
         earlyprintk=    [X86,SH,BLACKFIN,ARM]
                         earlyprintk=vga
                         earlyprintk=efi