w1: new w1_ds2406 driver
Some preliminary work at making use of this driver led me to implement
CRC-16 checks on read and write to deal with the occasional glitchiness of
the 1-Wire bus. The revised driver (attached) returns an I/O error if the
CRC check fails. When reading the chip's state, either you get a valid
indication or you get an I/O error. When changing its state, either the
change is successful or an I/O error is returned.
Signed-off-by: Scott Alfter <scott@alfter.us>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/Documentation/w1/slaves/w1_ds2406 b/Documentation/w1/slaves/w1_ds2406
new file mode 100644
index 0000000..8137fe6
--- /dev/null
+++ b/Documentation/w1/slaves/w1_ds2406
@@ -0,0 +1,25 @@
+w1_ds2406 kernel driver
+=======================
+
+Supported chips:
+ * Maxim DS2406 (and other family 0x12) addressable switches
+
+Author: Scott Alfter <scott@alfter.us>
+
+Description
+-----------
+
+The w1_ds2406 driver allows connected devices to be switched on and off.
+These chips also provide 128 bytes of OTP EPROM, but reading/writing it is
+not supported. In TSOC-6 form, the DS2406 provides two switch outputs and
+can be provided with power on a dedicated input. In TO-92 form, it provides
+one output and uses parasitic power only.
+
+The driver provides two sysfs files. state is readable; it gives the
+current state of each switch, with PIO A in bit 0 and PIO B in bit 1. The
+driver ORs this state with 0x30, so shell scripts get an ASCII 0/1/2/3 to
+work with. output is writable; bits 0 and 1 control PIO A and B,
+respectively. Bits 2-7 are ignored, so it's safe to write ASCII data.
+
+CRCs are checked on read and write. Failed checks cause an I/O error to be
+returned. On a failed write, the switch status is not changed.