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>

1 files changed, 34 insertions, 0 deletions

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index bd7cc0527999..f1ea59b09444 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -350,3 +350,37 @@ config TRACE_SINK
 
           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.