xtensa: ISS: add host file-based simulated disk

Simdisk is a block device that maps to a file in the host file system.
It is usable for testing in the simulated environment, like xt-sim or
QEMU. Device binding to host file may be changed at runtime via proc
interface provided the device is not in use. Number of block devices
and initial binding to host files is controlled via kernel/module
parameters, with defaults specified in the kernel configuration.

Signed-off-by: Victor Prupis <vnp@tensilica.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/Kconfig

@@ -203,6 +203,42 @@ config BUILTIN_DTB
 	string "DTB to build into the kernel image"
 	depends on OF
 
+config BLK_DEV_SIMDISK
+	tristate "Host file-based simulated block device support"
+	default n
+	depends on XTENSA_PLATFORM_ISS
+	help
+	  Create block devices that map to files in the host file system.
+	  Device binding to host file may be changed at runtime via proc
+	  interface provided the device is not in use.
+
+config BLK_DEV_SIMDISK_COUNT
+	int "Number of host file-based simulated block devices"
+	range 1 10
+	depends on BLK_DEV_SIMDISK
+	default 2
+	help
+	  This is the default minimal number of created block devices.
+	  Kernel/module parameter 'simdisk_count' may be used to change this
+	  value at runtime. More file names (but no more than 10) may be
+	  specified as parameters, simdisk_count grows accordingly.
+
+config SIMDISK0_FILENAME
+	string "Host filename for the first simulated device"
+	depends on BLK_DEV_SIMDISK = y
+	default ""
+	help
+	  Attach a first simdisk to a host file. Conventionally, this file
+	  contains a root file system.
+
+config SIMDISK1_FILENAME
+	string "Host filename for the second simulated device"
+	depends on BLK_DEV_SIMDISK = y && BLK_DEV_SIMDISK_COUNT != 1
+	default ""
+	help
+	  Another simulated disk in a host file for a buildroot-independent
+	  storage.
+
 source "mm/Kconfig"
 
 source "drivers/pcmcia/Kconfig"

arch/xtensa/platforms/iss/Makefile

@@ -6,3 +6,4 @@
 
 obj-y			= console.o setup.o
 obj-$(CONFIG_NET)	+= network.o
+obj-$(CONFIG_BLK_DEV_SIMDISK) += simdisk.o