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>

arch/powerpc/include/asm/udbg.h

@@ -54,6 +54,7 @@ extern void __init udbg_init_40x_realmode(void);
 extern void __init udbg_init_cpm(void);
 extern void __init udbg_init_usbgecko(void);
 extern void __init udbg_init_wsp(void);
+extern void __init udbg_init_ehv_bc(void);
 
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_UDBG_H */

arch/powerpc/kernel/udbg.c

@@ -67,6 +67,8 @@ void __init udbg_early_init(void)
 	udbg_init_usbgecko();
 #elif defined(CONFIG_PPC_EARLY_DEBUG_WSP)
 	udbg_init_wsp();
+#elif defined(CONFIG_PPC_EARLY_DEBUG_EHV_BC)
+	udbg_init_ehv_bc();
 #endif
 
 #ifdef CONFIG_PPC_EARLY_DEBUG

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.

drivers/tty/Makefile

@@ -26,5 +26,6 @@ obj-$(CONFIG_ROCKETPORT)	+= rocket.o
 obj-$(CONFIG_SYNCLINK_GT)	+= synclink_gt.o
 obj-$(CONFIG_SYNCLINKMP)	+= synclinkmp.o
 obj-$(CONFIG_SYNCLINK)		+= synclink.o
+obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o
 
 obj-y += ipwireless/