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, 10 insertions, 0 deletions

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 4290d05875b1..988fa2b6243b 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -73,6 +73,16 @@ config SERIAL_AMBA_PL011_CONSOLE
           your boot loader (lilo or loadlin) about how to pass options to the
           kernel at boot time.)
 
+config SERIAL_EARLYCON_ARM_SEMIHOST
+        bool "Early console using ARM semihosting"
+        depends on ARM64 || ARM
+        select SERIAL_EARLYCON
+        help
+          Support for early debug console using ARM semihosting. This enables
+          the console before standard serial driver is probed. This is enabled
+          with "earlycon=smh" on the kernel command line. The console is
+          enabled when early_param is processed.
+
 config SERIAL_SB1250_DUART
         tristate "BCM1xxx on-chip DUART serial support"
         depends on SIBYTE_SB1xxx_SOC=y