add w1_ds28e17 driver for the DS28E17 Onewire to I2C master bridge

This subpatch adds a driver for the DS28E17 Onewire to I2C master bridge.
Signed-off-by: Jan Kandziora <jjj@gmx.de>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-driver-w1_ds28e17

+What:		/sys/bus/w1/devices/19-<id>/speed
+Date:		Sep 2017
+KernelVersion:	4.14
+Contact:	Jan Kandziora <jjj@gmx.de>
+Description:	When written, this file sets the I2C speed on the connected
+		DS28E17 chip. When read, it reads the current setting from
+		the DS28E17 chip.
+		Valid values: 100, 400, 900 [kBaud].
+		Default 100, can be set by w1_ds28e17.speed= module parameter.
+Users:		w1_ds28e17 driver
+
+What:		/sys/bus/w1/devices/19-<id>/stretch
+Date:		Sep 2017
+KernelVersion:	4.14
+Contact:	Jan Kandziora <jjj@gmx.de>
+Description:	When written, this file sets the multiplier used to calculate
+		the busy timeout for I2C operations on the connected DS28E17
+		chip. When read, returns the current setting.
+		Valid values: 1 to 9.
+		Default 1, can be set by w1_ds28e17.stretch= module parameter.
+Users:		w1_ds28e17 driver

Documentation/w1/slaves/00-INDEX

@@ -10,3 +10,5 @@ w1_ds2438
 	- The Maxim/Dallas Semiconductor ds2438 smart battery monitor.
 w1_ds28e04
 	- The Maxim/Dallas Semiconductor ds28e04 eeprom.
+w1_ds28e17
+	- The Maxim/Dallas Semiconductor ds28e17 1-Wire-to-I2C Master Bridge.

Documentation/w1/slaves/w1_ds28e17

+Kernel driver w1_ds28e17
+========================
+
+Supported chips:
+  * Maxim DS28E17 1-Wire-to-I2C Master Bridge
+
+supported family codes:
+	W1_FAMILY_DS28E17  0x19
+
+Author: Jan Kandziora <jjj@gmx.de>
+
+
+Description
+-----------
+The DS28E17 is a Onewire slave device which acts as an I2C bus master.
+
+This driver creates a new I2C bus for any DS28E17 device detected. I2C buses
+come and go as the DS28E17 devices come and go. I2C slave devices connected to
+a DS28E17 can be accessed by the kernel or userspace tools as if they were
+connected to a "native" I2C bus master.
+
+
+An udev rule like the following
+-------------------------------------------------------------------------------
+SUBSYSTEM=="i2c-dev", KERNEL=="i2c-[0-9]*", ATTRS{name}=="w1-19-*", \
+        SYMLINK+="i2c-$attr{name}"
+-------------------------------------------------------------------------------
+may be used to create stable /dev/i2c- entries based on the unique id of the
+DS28E17 chip.
+
+
+Driver parameters are:
+
+speed:
+	This sets up the default I2C speed a DS28E17 get configured for as soon
+	it is connected. The power-on default	of the DS28E17 is 400kBaud, but
+	chips may come and go on the Onewire bus without being de-powered and
+	as soon the "w1_ds28e17" driver notices a freshly connected, or
+	reconnected DS28E17 device on the Onewire bus, it will re-apply this
+	setting.
+
+	Valid values are 100, 400, 900 [kBaud]. Any other value means to leave
+	alone the current DS28E17 setting on detect. The default value is 100.
+
+stretch:
+	This sets up the default stretch value used for freshly connected
+	DS28E17 devices. It is a multiplier used on the calculation of the busy
+	wait time for an I2C transfer. This is to account for I2C slave devices
+	which make heavy use of the I2C clock stretching feature and thus, the
+	needed timeout cannot be pre-calculated correctly. As the w1_ds28e17
+	driver checks the DS28E17's busy flag in a loop after the precalculated
+	wait time, it should be hardly needed to tweak this setting.
+
+	Leave it at 1 unless you get ETIMEDOUT errors and a "w1_slave_driver
+	19-00000002dbd8: busy timeout" in the kernel log.
+
+	Valid values are 1 to 9. The default is 1.
+
+
+The driver creates sysfs files /sys/bus/w1/devices/19-<id>/speed and
+/sys/bus/w1/devices/19-<id>/stretch for each device, preloaded with the default
+settings from the driver parameters. They may be changed anytime. In addition a
+directory /sys/bus/w1/devices/19-<id>/i2c-<nnn> for the I2C bus master sysfs
+structure is created.
+
+
+See https://github.com/ianka/w1_ds28e17 for even more information.
+

drivers/w1/slaves/Kconfig

@@ -148,4 +148,19 @@ config W1_SLAVE_DS28E04
 
 	  If you are unsure, say N.
 
+config W1_SLAVE_DS28E17
+	tristate "1-wire-to-I2C master bridge (DS28E17)"
+	select CRC16
+	depends on I2C
+	help
+	  Say Y here if you want to use the DS28E17 1-wire-to-I2C master bridge.
+	  For each DS28E17 detected, a new I2C adapter is created within the
+	  kernel. I2C devices on that bus can be configured to be used by the
+	  kernel and userspace tools as on any other "native" I2C bus.
+
+	  This driver is also available as a module. If so, the module
+	  will be called w1_ds28e17.
+
+	  If you are unsure, say N.
+
 endmenu

drivers/w1/slaves/Makefile

@@ -17,3 +17,4 @@ obj-$(CONFIG_W1_SLAVE_DS2760)	+= w1_ds2760.o
 obj-$(CONFIG_W1_SLAVE_DS2780)	+= w1_ds2780.o
 obj-$(CONFIG_W1_SLAVE_DS2781)	+= w1_ds2781.o
 obj-$(CONFIG_W1_SLAVE_DS28E04)	+= w1_ds28e04.o
+obj-$(CONFIG_W1_SLAVE_DS28E17)	+= w1_ds28e17.o