tty/powerpc: introduce the ePAPR embedded hypervisor byte channel driver
The ePAPR embedded hypervisor specification provides an API for "byte
channels", which are serial-like virtual devices for sending and receiving
streams of bytes. This driver provides Linux kernel support for byte
channels via three distinct interfaces:
1) An early-console (udbg) driver. This provides early console output
through a byte channel. The byte channel handle must be specified in a
Kconfig option.
2) A normal console driver. Output is sent to the byte channel designated
for stdout in the device tree. The console driver is for handling kernel
printk calls.
3) A tty driver, which is used to handle user-space input and output. The
byte channel used for the console is designated as the default tty.
Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index bd7cc05..f1ea59b 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -350,3 +350,37 @@
If you select this option, you need to select
"Trace data router for MIPI P1149.7 cJTAG standard".
+
+config PPC_EPAPR_HV_BYTECHAN
+ tristate "ePAPR hypervisor byte channel driver"
+ depends on PPC
+ help
+ This driver creates /dev entries for each ePAPR hypervisor byte
+ channel, thereby allowing applications to communicate with byte
+ channels as if they were serial ports.
+
+config PPC_EARLY_DEBUG_EHV_BC
+ bool "Early console (udbg) support for ePAPR hypervisors"
+ depends on PPC_EPAPR_HV_BYTECHAN
+ help
+ Select this option to enable early console (a.k.a. "udbg") support
+ via an ePAPR byte channel. You also need to choose the byte channel
+ handle below.
+
+config PPC_EARLY_DEBUG_EHV_BC_HANDLE
+ int "Byte channel handle for early console (udbg)"
+ depends on PPC_EARLY_DEBUG_EHV_BC
+ default 0
+ help
+ If you want early console (udbg) output through a byte channel,
+ specify the handle of the byte channel to use.
+
+ For this to work, the byte channel driver must be compiled
+ in-kernel, not as a module.
+
+ Note that only one early console driver can be enabled, so don't
+ enable any others if you enable this one.
+
+ If the number you specify is not a valid byte channel handle, then
+ there simply will be no early console output. This is true also
+ if you don't boot under a hypervisor at all.