[S390] cio: Add chsc subchannel driver.

This patch adds a driver for subchannels of type chsc.

A device /dev/chsc is created which may be used to issue ioctls to:
- obtain information about the machine's I/O configuration
- dynamically change the machine's I/O configuration via
  asynchronous chsc commands

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index a79820c..6d0d3165 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -345,6 +345,22 @@
 
 	  If unsure, say N.
 
+config CHSC_SCH
+	tristate "Support for CHSC subchannels"
+	help
+	  This driver allows usage of CHSC subchannels. A CHSC subchannel
+	  is usually present on LPAR only.
+	  The driver creates a device /dev/chsc, which may be used to
+	  obtain I/O configuration information about the machine and
+	  to issue asynchronous chsc commands (DANGEROUS).
+	  You will usually only want to use this interface on a special
+	  LPAR designated for system management.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called chsc_sch.
+
+	  If unsure, say N.
+
 comment "Misc"
 
 config IPL