Move the pcf8591 driver to hwmon

Directory drivers/i2c/chips is going away, so drivers there must find
new homes. For the pcf8591 driver, the best choice seems to be the
hwmon subsystem. While the Philips PCF8591 device isn't a typical
hardware monitoring chip, its DAC interface is compatible with the
hwmon one, so it fits somewhat.

If a better subsystem is ever created for ADC/DAC chips, the driver
could be moved there.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 90 insertions, 0 deletions

diff --git a/Documentation/hwmon/pcf8591 b/Documentation/hwmon/pcf8591
new file mode 100644
index 000000000000..5628fcf4207f
--- /dev/null
+++ b/Documentation/hwmon/pcf8591
@@ -0,0 +1,90 @@
+Kernel driver pcf8591
+=====================
+
+Supported chips:
+  * Philips PCF8591
+    Prefix: 'pcf8591'
+    Addresses scanned: I2C 0x48 - 0x4f
+    Datasheet: Publicly available at the Philips Semiconductor website
+               http://www.semiconductors.philips.com/pip/PCF8591P.html
+
+Authors:
+        Aurelien Jarno <aurelien@aurel32.net>
+        valuable contributions by Jan M. Sendler <sendler@sendler.de>,
+        Jean Delvare <khali@linux-fr.org>
+
+
+Description
+-----------
+The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one
+analog output) for the I2C bus produced by Philips Semiconductors. It
+is designed to provide a byte I2C interface to up to 4 separate devices.
+
+The PCF8591 has 4 analog inputs programmable as single-ended or
+differential inputs :
+- mode 0 : four single ended inputs
+        Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
+
+- mode 1 : three differential inputs
+        Pins AIN3 is the common negative differential input
+        Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2
+
+- mode 2 : single ended and differential mixed
+        Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
+        Pins AIN2 is the positive differential input for channel 3
+        Pins AIN3 is the negative differential input for channel 3
+
+- mode 3 : two differential inputs
+        Pins AIN0 is the positive differential input for channel 0
+        Pins AIN1 is the negative differential input for channel 0
+        Pins AIN2 is the positive differential input for channel 1
+        Pins AIN3 is the negative differential input for channel 1
+
+See the datasheet for details.
+
+Module parameters
+-----------------
+
+* input_mode int
+
+    Analog input mode:
+         0 = four single ended inputs
+         1 = three differential inputs
+         2 = single ended and differential mixed
+         3 = two differential inputs
+
+
+Accessing PCF8591 via /sys interface
+-------------------------------------
+
+! Be careful !
+The PCF8591 is plainly impossible to detect ! Stupid chip.
+So every chip with address in the interval [48..4f] is
+detected as PCF8591. If you have other chips in this address
+range, the workaround is to load this module after the one
+for your others chips.
+
+On detection (i.e. insmod, modprobe et al.), directories are being
+created for each detected PCF8591:
+
+/sys/bus/devices/<0>-<1>/
+where <0> is the bus the chip was detected on (e. g. i2c-0)
+and <1> the chip address ([48..4f])
+
+Inside these directories, there are such files:
+in0, in1, in2, in3, out0_enable, out0_output, name
+
+Name contains chip name.
+
+The in0, in1, in2 and in3 files are RO. Reading gives the value of the
+corresponding channel. Depending on the current analog inputs configuration,
+files in2 and/or in3 do not exist. Values range are from 0 to 255 for single
+ended inputs and -128 to +127 for differential inputs (8-bit ADC).
+
+The out0_enable file is RW. Reading gives "1" for analog output enabled and
+"0" for analog output disabled. Writing accepts "0" and "1" accordingly.
+
+The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send
+the value to the digital-to-analog converter. Note that a voltage will
+only appears on AOUT pin if aout0_enable equals 1. Reading returns the last
+value written.