eeprom: Add IDT 89HPESx EEPROM/CSR driver

  This driver provides an access to EEPROM of IDT PCIe-switches. IDT PCIe-
switches expose a simple SMBus interface to perform IO-operations from/to
EEPROM, which is located at private (so called Master) SMBus. The driver
creates a simple binary sysfs-file to have an access to the EEPROM using
the SMBus-slave interface in the i2c-device susfs-directory:
     /sys/bus/i2c/devices/<bus>-<devaddr>/eeprom
In case if read-only flag is specified at dts-node of the device, User-space
applications won't be able to write to the EEPROM sysfs-node.

  Additionally IDT 89HPESx SMBus interface has an ability to read/write
values of device CSRs. This driver exposes debugfs-file to perform simple
IO-operations using that ability for just basic debug purpose. Particularly
the next file is created in the specific debugfs-directory:
     /sys/kernel/debug/idt_csr/
Format of the debugfs-file value is:
     $ cat /sys/kernel/debug/idt_csr/<bus>-<devaddr>/<devname>;
     <CSR address>:<CSR value>
So reading the content of the file gives current CSR address and it value.
If User-space application wishes to change current CSR address, it can just
write a proper value to the sysfs-file:
     $ echo "<CSR address>" >
         /sys/kernel/debug/idt_csr/<bus>-<devaddr>/<devname>
If it wants to change the CSR value as well, the format of the write
operation is:
     $ echo "<CSR address>:<CSR value>" > \
         /sys/kernel/debug/idt_csr/<bus>-<devaddr>/<devname>;
CSR address and value can be any of hexadecimal, decimal or octal format.
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/eeprom/Kconfig

@@ -100,4 +100,14 @@ config EEPROM_DIGSY_MTC_CFG
 
 	  If unsure, say N.
 
+config EEPROM_IDT_89HPESX
+	tristate "IDT 89HPESx PCIe-swtiches EEPROM / CSR support"
+	depends on I2C && SYSFS
+	help
+	  Enable this driver to get read/write access to EEPROM / CSRs
+	  over IDT PCIe-swtich i2c-slave interface.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called idt_89hpesx.
+
 endmenu

drivers/misc/eeprom/Makefile

@@ -5,3 +5,4 @@ obj-$(CONFIG_EEPROM_MAX6875)	+= max6875.o
 obj-$(CONFIG_EEPROM_93CX6)	+= eeprom_93cx6.o
 obj-$(CONFIG_EEPROM_93XX46)	+= eeprom_93xx46.o
 obj-$(CONFIG_EEPROM_DIGSY_MTC_CFG) += digsy_mtc_eeprom.o
+obj-$(CONFIG_EEPROM_IDT_89HPESX) += idt_89hpesx.o