Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+Kernel driver pcf8591
+=====================
+
+Supported chips:
+  * Philips/NXP PCF8591
+    Prefix: 'pcf8591'
+    Addresses scanned: none
+    Datasheet: Publicly available at the NXP website
+               http://www.nxp.com/pip/PCF8591_6.html
+
+Authors:
+        Aurelien Jarno <aurelien@aurel32.net>
+        valuable contributions by Jan M. Sendler <sendler@sendler.de>,
+        Jean Delvare <jdelvare@suse.de>
+
+
+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 (now NXP).
+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
+-------------------------------------
+
+The PCF8591 is plainly impossible to detect! Thus the driver won't even
+try. You have to explicitly instantiate the device at the relevant
+address (in the interval [0x48..0x4f]) either through platform data, or
+using the sysfs interface. See Documentation/i2c/instantiating-devices
+for details.
+
+Directories are being created for each instantiated PCF8591:
+
+/sys/bus/i2c/devices/<0>-<1>/
+where <0> is the bus the chip is connected to (e. g. i2c-0)
+and <1> the chip address ([48..4f])
+
+Inside these directories, there are such files:
+in0_input, in1_input, in2_input, in3_input, out0_enable, out0_output, name
+
+Name contains chip name.
+
+The in0_input, in1_input, in2_input and in3_input files are RO. Reading gives
+the value of the corresponding channel. Depending on the current analog inputs
+configuration, files in2_input and in3_input may not exist. Values range
+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.