Introduce the Counter subsystem

index 83a439c65925..7f0ab08184d8 100644
@@ -3706,6 +3706,14 @@ W:	http://www.fi.muni.cz/~kas/cosa/
 S:	Maintained
 F:	drivers/net/wan/cosa*
 
+COUNTER SUBSYSTEM
+M:	William Breathitt Gray <[email protected]>
+L:	linux-iio at vger.kernel.org
+S:	Maintained
+F:	drivers/counter/
+F:	include/linux/counter.h
+F:	include/linux/counter_enum.h
+
 CPMAC ETHERNET DRIVER
 M:	Florian Fainelli <[email protected]>
 L:	netdev at vger.kernel.org

index 95b9ccc08165..6932ac9316e0 100644
@@ -217,4 +217,6 @@ source "drivers/siox/Kconfig"
 
 source "drivers/slimbus/Kconfig"
 
+source "drivers/counter/Kconfig"
+
 endmenu

index 24cd47014657..ae9596976372 100644
@@ -185,3 +185,4 @@ obj-$(CONFIG_TEE)		+= tee/
 obj-$(CONFIG_MULTIPLEXER)	+= mux/
 obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
 obj-$(CONFIG_SIOX)		+= siox/
+obj-$(CONFIG_COUNTER)		+= counter/

new file mode 100644
index 000000000000..a74998400282
@@ -0,0 +1,10 @@
+#
+# Counter devices
+#
+
+menuconfig COUNTER
+	tristate "Counter support"
+	help
+	  This enables counter device support through the Generic Counter
+	  interface. You only need to enable this, if you also want to enable
+	  one or more of the counter device drivers below.

new file mode 100644
index 000000000000..b1464604bdbe
@@ -0,0 +1,5 @@
+#
+# Makefile for Counter devices
+#
+
+obj-$(CONFIG_COUNTER) += counter.o

new file mode 100644
index 000000000000..62d4a931326a
@@ -0,0 +1,230 @@
+What:		/sys/bus/counter/devices/counterX/countY/count
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Count data of Count Y represented as a string.
+
+What:		/sys/bus/counter/devices/counterX/countY/ceiling
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Count value ceiling for Count Y. This is the upper limit for the
+		respective counter.
+
+What:		/sys/bus/counter/devices/counterX/countY/floor
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Count value floor for Count Y. This is the lower limit for the
+		respective counter.
+
+What:		/sys/bus/counter/devices/counterX/countY/count_mode
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Count mode for channel Y. The ceiling and floor values for
+		Count Y are used by the count mode where required. The following
+		count modes are available:
+
+		normal:
+			Counting is continuous in either direction.
+
+		range limit:
+			An upper or lower limit is set, mimicking limit switches
+			in the mechanical counterpart. The upper limit is set to
+			the Count Y ceiling value, while the lower limit is set
+			to the Count Y floor value. The counter freezes at
+			count = ceiling when counting up, and at count = floor
+			when counting down. At either of these limits, the
+			counting is resumed only when the count direction is
+			reversed.
+
+		non-recycle:
+			The counter is disabled whenever a counter overflow or
+			underflow takes place. The counter is re-enabled when a
+			new count value is loaded to the counter via a preset
+			operation or direct write.
+
+		modulo-n:
+			A count value boundary is set between the Count Y floor
+			value and the Count Y ceiling value. The counter is
+			reset to the Cunt Y floor value at count = ceiling when
+			counting up, while the counter is set to the Count Y
+			ceiling value at count = floor when counting down; the
+			counter does not freeze at the boundary points, but
+			counts continuously throughout.
+
+What:		/sys/bus/counter/devices/counterX/countY/count_mode_available
+What:		/sys/bus/counter/devices/counterX/countY/error_noise_available
+What:		/sys/bus/counter/devices/counterX/countY/function_available
+What:		/sys/bus/counter/devices/counterX/countY/signalZ_action_available
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Discrete set of available values for the respective Count Y
+		configuration are listed in this file. Values are delineated by
+		newline characters.
+
+What:		/sys/bus/counter/devices/counterX/countY/direction
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Read-only attribute that indicates the count direction of Count
+		Y. Two count directions are available: forward and backward.
+
+		Some counter devices are able to determine the direction of
+		their counting. For example, quadrature encoding counters can
+		determine the direction of movement by evaluating the leading
+		phase of the respective A and B quadrature encoding signals.
+		This attribute exposes such count directions.
+
+What:		/sys/bus/counter/devices/counterX/countY/enable
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Whether channel Y counter is enabled. Valid attribute values are
+		boolean.
+
+		This attribute is intended to serve as a pause/unpause mechanism
+		for Count Y. Suppose a counter device is used to count the total
+		movement of a conveyor belt: this attribute allows an operator
+		to temporarily pause the counter, service the conveyor belt,
+		and then finally unpause the counter to continue where it had
+		left off.
+
+What:		/sys/bus/counter/devices/counterX/countY/error_noise
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Read-only attribute that indicates whether excessive noise is
+		present at the channel Y counter inputs.
+
+What:		/sys/bus/counter/devices/counterX/countY/function
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Count function mode of Count Y; count function evaluation is
+		triggered by conditions specified by the Count Y signalZ_action
+		attributes. The following count functions are available:
+
+		increase:
+			Accumulated count is incremented.
+
+		decrease:
+			Accumulated count is decremented.
+
+		pulse-direction:
+			Rising edges on signal A updates the respective count.
+			The input level of signal B determines direction.
+
+		quadrature x1 a:
+			If direction is forward, rising edges on quadrature pair
+			signal A updates the respective count; if the direction
+			is backward, falling edges on quadrature pair signal A
+			updates the respective count. Quadrature encoding
+			determines the direction.
+
+		quadrature x1 b:
+			If direction is forward, rising edges on quadrature pair
+			signal B updates the respective count; if the direction
+			is backward, falling edges on quadrature pair signal B
+			updates the respective count. Quadrature encoding
+			determines the direction.
+
+		quadrature x2 a:
+			Any state transition on quadrature pair signal A updates
+			the respective count. Quadrature encoding determines the
+			direction.
+
+		quadrature x2 b:
+			Any state transition on quadrature pair signal B updates
+			the respective count. Quadrature encoding determines the
+			direction.
+
+		quadrature x4:
+			Any state transition on either quadrature pair signals
+			updates	the respective count. Quadrature encoding
+			determines the direction.
+
+What:		/sys/bus/counter/devices/counterX/countY/name
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Read-only attribute that indicates the device-specific name of
+		Count Y. If possible, this should match the name of the
+		respective channel as it appears in the device datasheet.
+
+What:		/sys/bus/counter/devices/counterX/countY/preset
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		If the counter device supports preset registers -- registers
+		used to load counter channels to a set count upon device-defined
+		preset operation trigger events -- the preset count for channel
+		Y is provided by this attribute.
+
+What:		/sys/bus/counter/devices/counterX/countY/preset_enable
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Whether channel Y counter preset operation is enabled. Valid
+		attribute values are boolean.
+
+What:		/sys/bus/counter/devices/counterX/countY/signalZ_action
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Action mode of Count Y for Signal Z. This attribute indicates
+		the condition of Signal Z that triggers the count function
+		evaluation for Count Y. The following action modes are
+		available:
+
+		none:
+			Signal does not trigger the count function. In
+			Pulse-Direction count function mode, this Signal is
+			evaluated as Direction.
+
+		rising edge:
+			Low state transitions to high state.
+
+		falling edge:
+			High state transitions to low state.
+
+		both edges:
+			Any state transition.
+
+What:		/sys/bus/counter/devices/counterX/name
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Read-only attribute that indicates the device-specific name of
+		the Counter. This should match the name of the device as it
+		appears in its respective datasheet.
+
+What:		/sys/bus/counter/devices/counterX/num_counts
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Read-only attribute that indicates the total number of Counts
+		belonging to the Counter.
+
+What:		/sys/bus/counter/devices/counterX/num_signals
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Read-only attribute that indicates the total number of Signals
+		belonging to the Counter.
+
+What:		/sys/bus/counter/devices/counterX/signalY/signal
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Signal data of Signal Y represented as a string.
+
+What:		/sys/bus/counter/devices/counterX/signalY/name
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Read-only attribute that indicates the device-specific name of
+		Signal Y. If possible, this should match the name of the
+		respective signal as it appears in the device datasheet.

index 7f0ab08184d8..46bff1b47d83 100644
@@ -3710,6 +3710,7 @@ COUNTER SUBSYSTEM
 M:	William Breathitt Gray <[email protected]>
 L:	linux-iio at vger.kernel.org
 S:	Maintained
+F:	Documentation/ABI/testing/sysfs-bus-counter*
 F:	drivers/counter/
 F:	include/linux/counter.h
 F:	include/linux/counter_enum.h

new file mode 100644
index 000000000000..f51db893f595
@@ -0,0 +1,342 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+Generic Counter Interface
+=========================
+
+Introduction
+============
+
+Counter devices are prevalent within a diverse spectrum of industries.
+The ubiquitous presence of these devices necessitates a common interface
+and standard of interaction and exposure. This driver API attempts to
+resolve the issue of duplicate code found among existing counter device
+drivers by introducing a generic counter interface for consumption. The
+Generic Counter interface enables drivers to support and expose a common
+set of components and functionality present in counter devices.
+
+Theory
+======
+
+Counter devices can vary greatly in design, but regardless of whether
+some devices are quadrature encoder counters or tally counters, all
+counter devices consist of a core set of components. This core set of
+components, shared by all counter devices, is what forms the essence of
+the Generic Counter interface.
+
+There are three core components to a counter:
+
+* Count:
+  Count data for a set of Signals.
+
+* Signal:
+  Input data that is evaluated by the counter to determine the count
+  data.
+
+* Synapse:
+  The association of a Signal with a respective Count.
+
+COUNT
+-----
+A Count represents the count data for a set of Signals. The Generic
+Counter interface provides the following available count data types:
+
+* COUNT_POSITION:
+  Unsigned integer value representing position.
+
+A Count has a count function mode which represents the update behavior
+for the count data. The Generic Counter interface provides the following
+available count function modes:
+
+* Increase:
+  Accumulated count is incremented.
+
+* Decrease:
+  Accumulated count is decremented.
+
+* Pulse-Direction:
+  Rising edges on signal A updates the respective count. The input level
+  of signal B determines direction.
+
+* Quadrature:
+  A pair of quadrature encoding signals are evaluated to determine
+  position and direction. The following Quadrature modes are available:
+
+  - x1 A:
+    If direction is forward, rising edges on quadrature pair signal A
+    updates the respective count; if the direction is backward, falling
+    edges on quadrature pair signal A updates the respective count.
+    Quadrature encoding determines the direction.
+
+  - x1 B:
+    If direction is forward, rising edges on quadrature pair signal B
+    updates the respective count; if the direction is backward, falling
+    edges on quadrature pair signal B updates the respective count.
+    Quadrature encoding determines the direction.
+
+  - x2 A:
+    Any state transition on quadrature pair signal A updates the
+    respective count. Quadrature encoding determines the direction.
+
+  - x2 B:
+    Any state transition on quadrature pair signal B updates the
+    respective count. Quadrature encoding determines the direction.
+
+  - x4:
+    Any state transition on either quadrature pair signals updates the
+    respective count. Quadrature encoding determines the direction.
+
+A Count has a set of one or more associated Signals.
+
+SIGNAL
+------
+A Signal represents a counter input data; this is the input data that is
+evaluated by the counter to determine the count data; e.g. a quadrature
+signal output line of a rotary encoder. Not all counter devices provide
+user access to the Signal data.
+
+The Generic Counter interface provides the following available signal
+data types for when the Signal data is available for user access:
+
+* SIGNAL_LEVEL:
+  Signal line state level. The following states are possible:
+
+  - SIGNAL_LEVEL_LOW:
+    Signal line is in a low state.
+
+  - SIGNAL_LEVEL_HIGH:
+    Signal line is in a high state.
+
+A Signal may be associated with one or more Counts.
+
+SYNAPSE
+-------
+A Synapse represents the association of a Signal with a respective
+Count. Signal data affects respective Count data, and the Synapse
+represents this relationship.
+
+The Synapse action mode specifies the Signal data condition which
+triggers the respective Count's count function evaluation to update the
+count data. The Generic Counter interface provides the following
+available action modes:
+
+* None:
+  Signal does not trigger the count function. In Pulse-Direction count
+  function mode, this Signal is evaluated as Direction.
+
+* Rising Edge:
+  Low state transitions to high state.
+
+* Falling Edge:
+  High state transitions to low state.
+
+* Both Edges:
+  Any state transition.
+
+A counter is defined as a set of input signals associated with count
+data that are generated by the evaluation of the state of the associated
+input signals as defined by the respective count functions. Within the
+context of the Generic Counter interface, a counter consists of Counts
+each associated with a set of Signals, whose respective Synapse
+instances represent the count function update conditions for the
+associated Counts.
+
+Paradigm
+========
+
+The most basic counter device may be expressed as a single Count
+associated with a single Signal via a single Synapse. Take for example
+a counter device which simply accumulates a count of rising edges on a
+source input line::
+
+                Count                Synapse        Signal
+                -----                -------        ------
+        +---------------------+
+        | Data: Count         |    Rising Edge     ________
+        | Function: Increase  |  <-------------   / Source \
+        |                     |                  ____________
+        +---------------------+
+
+In this example, the Signal is a source input line with a pulsing
+voltage, while the Count is a persistent count value which is repeatedly
+incremented. The Signal is associated with the respective Count via a
+Synapse. The increase function is triggered by the Signal data condition
+specified by the Synapse -- in this case a rising edge condition on the
+voltage input line. In summary, the counter device existence and
+behavior is aptly represented by respective Count, Signal, and Synapse
+components: a rising edge condition triggers an increase function on an
+accumulating count datum.
+
+A counter device is not limited to a single Signal; in fact, in theory
+many Signals may be associated with even a single Count. For example, a
+quadrature encoder counter device can keep track of position based on
+the states of two input lines::
+
+                   Count                 Synapse     Signal
+                   -----                 -------     ------
+        +-------------------------+
+        | Data: Position          |    Both Edges     ___
+        | Function: Quadrature x4 |  <------------   / A \
+        |                         |                 _______
+        |                         |
+        |                         |    Both Edges     ___
+        |                         |  <------------   / B \
+        |                         |                 _______
+        +-------------------------+
+
+In this example, two Signals (quadrature encoder lines A and B) are
+associated with a single Count: a rising or falling edge on either A or
+B triggers the "Quadrature x4" function which determines the direction
+of movement and updates the respective position data. The "Quadrature
+x4" function is likely implemented in the hardware of the quadrature
+encoder counter device; the Count, Signals, and Synapses simply
+represent this hardware behavior and functionality.
+
+Signals associated with the same Count can have differing Synapse action
+mode conditions. For example, a quadrature encoder counter device
+operating in a non-quadrature Pulse-Direction mode could have one input
+line dedicated for movement and a second input line dedicated for
+direction::
+
+                   Count                   Synapse      Signal
+                   -----                   -------      ------
+        +---------------------------+
+        | Data: Position            |    Rising Edge     ___
+        | Function: Pulse-Direction |  <-------------   / A \ (Movement)
+        |                           |                  _______
+        |                           |
+        |                           |       None         ___
+        |                           |  <-------------   / B \ (Direction)
+        |                           |                  _______
+        +---------------------------+
+
+Only Signal A triggers the "Pulse-Direction" update function, but the
+instantaneous state of Signal B is still required in order to know the
+direction so that the position data may be properly updated. Ultimately,
+both Signals are associated with the same Count via two respective
+Synapses, but only one Synapse has an active action mode condition which
+triggers the respective count function while the other is left with a
+"None" condition action mode to indicate its respective Signal's
+availability for state evaluation despite its non-triggering mode.
+
+Keep in mind that the Signal, Synapse, and Count are abstract
+representations which do not need to be closely married to their
+respective physical sources. This allows the user of a counter to
+divorce themselves from the nuances of physical components (such as
+whether an input line is differential or single-ended) and instead focus
+on the core idea of what the data and process represent (e.g. position
+as interpreted from quadrature encoding data).
+
+Userspace Interface
+===================
+
+Several sysfs attributes are generated by the Generic Counter interface,
+and reside under the /sys/bus/counter/devices/counterX directory, where
+counterX refers to the respective counter device. Please see
+Documentation/ABI/testing/sys-bus-counter-generic-sysfs for detailed
+information on each Generic Counter interface sysfs attribute.
+
+Through these sysfs attributes, programs and scripts may interact with
+the Generic Counter paradigm Counts, Signals, and Synapses of respective
+counter devices.
+
+Driver API
+==========
+
+Driver authors may utilize the Generic Counter interface in their code
+by including the include/linux/counter.h header file. This header file
+provides several core data structures, function prototypes, and macros
+for defining a counter device.
+
+.. kernel-doc:: include/linux/counter.h
+   :internal:
+
+.. kernel-doc:: drivers/counter/generic-counter.c
+   :export:
+
+Implementation
+==============
+
+To support a counter device, a driver must first allocate the available
+Counter Signals via counter_signal structures. These Signals should
+be stored as an array and set to the signals array member of an
+allocated counter_device structure before the Counter is registered to
+the system.
+
+Counter Counts may be allocated via counter_count structures, and
+respective Counter Signal associations (Synapses) made via
+counter_synapse structures. Associated counter_synapse structures are
+stored as an array and set to the the synapses array member of the
+respective counter_count structure. These counter_count structures are
+set to the counts array member of an allocated counter_device structure
+before the Counter is registered to the system.
+
+Driver callbacks should be provided to the counter_device structure via
+a constant counter_ops structure in order to communicate with the
+device: to read and write various Signals and Counts, and to set and get
+the "action mode" and "function mode" for various Synapses and Counts
+respectively.
+
+A defined counter_device structure may be registered to the system by
+passing it to the counter_register function, and unregistered by passing
+it to the counter_unregister function. Similarly, the
+devm_counter_register and devm_counter_unregister functions may be used
+if device memory-managed registration is desired.
+
+Extension sysfs attributes can be created for auxiliary functionality
+and data by passing in defined counter_device_ext, counter_count_ext,
+and counter_signal_ext structures. In these cases, the
+counter_device_ext structure is used for global configuration of the
+respective Counter device, while the counter_count_ext and
+counter_signal_ext structures allow for auxiliary exposure and
+configuration of a specific Count or Signal respectively.
+
+Architecture
+============
+
+When the Generic Counter interface counter module is loaded, the
+counter_init function is called which registers a bus_type named
+"counter" to the system. Subsequently, when the module is unloaded, the
+counter_exit function is called which unregisters the bus_type named
+"counter" from the system.
+
+Counter devices are registered to the system via the counter_register
+function, and later removed via the counter_unregister function. The
+counter_register function establishes a unique ID for the Counter
+device and creates a respective sysfs directory, where X is the
+mentioned unique ID:
+
+    /sys/bus/counter/devices/counterX
+
+Sysfs attributes are created within the counterX directory to expose
+functionality, configurations, and data relating to the Counts, Signals,
+and Synapses of the Counter device, as well as options and information
+for the Counter device itself.
+
+Each Signal has a directory created to house its relevant sysfs
+attributes, where Y is the unique ID of the respective Signal:
+
+    /sys/bus/counter/devices/counterX/signalY
+
+Similarly, each Count has a directory created to house its relevant
+sysfs attributes, where Y is the unique ID of the respective Count:
+
+    /sys/bus/counter/devices/counterX/countY
+
+For a more detailed breakdown of the available Generic Counter interface
+sysfs attributes, please refer to the
+Documentation/ABI/testing/sys-bus-counter file.
+
+The Signals and Counts associated with the Counter device are registered
+to the system as well by the counter_register function. The
+signal_read/signal_write driver callbacks are associated with their
+respective Signal attributes, while the count_read/count_write and
+function_get/function_set driver callbacks are associated with their
+respective Count attributes; similarly, the same is true for the
+action_get/action_set driver callbacks and their respective Synapse
+attributes. If a driver callback is left undefined, then the respective
+read/write permission is left disabled for the relevant attributes.
+
+Similarly, extension sysfs attributes are created for the defined
+counter_device_ext, counter_count_ext, and counter_signal_ext
+structures that are passed in.

index 6d9f2f9fe20e..fd8d76fa3760 100644
@@ -53,6 +53,7 @@ available subsections can be seen below.
    slimbus
    soundwire/index
    fpga/index
+   generic-counter
 
 .. only::  subproject and html
 

index 46bff1b47d83..08339129d342 100644
@@ -3711,6 +3711,7 @@ M:	William Breathitt Gray <[email protected]>
 L:	linux-iio at vger.kernel.org
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-bus-counter*
+F:	Documentation/driver-api/generic-counter.rst
 F:	drivers/counter/
 F:	include/linux/counter.h
 F:	include/linux/counter_enum.h

index 08339129d342..f41c45246e2b 100644
@@ -266,12 +266,12 @@ L:	linux-gpio at vger.kernel.org
 S:	Maintained
 F:	drivers/gpio/gpio-104-idio-16.c
 
-ACCES 104-QUAD-8 IIO DRIVER
+ACCES 104-QUAD-8 DRIVER
 M:	William Breathitt Gray <[email protected]>
 L:	linux-iio at vger.kernel.org
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-bus-iio-counter-104-quad-8
-F:	drivers/iio/counter/104-quad-8.c
+F:	drivers/counter/104-quad-8.c
 
 ACCES PCI-IDIO-16 GPIO DRIVER
 M:	William Breathitt Gray <[email protected]>

index a74998400282..dd3add729529 100644
@@ -8,3 +8,24 @@ menuconfig COUNTER
 	  This enables counter device support through the Generic Counter
 	  interface. You only need to enable this, if you also want to enable
 	  one or more of the counter device drivers below.
+
+if COUNTER
+
+config 104_QUAD_8
+	tristate "ACCES 104-QUAD-8 driver"
+	depends on PC104 && X86 && IIO
+	select ISA_BUS_API
+	help
+	  Say yes here to build support for the ACCES 104-QUAD-8 quadrature
+	  encoder counter/interface device family (104-QUAD-8, 104-QUAD-4).
+
+	  A counter's respective error flag may be cleared by performing a write
+	  operation on the respective count value attribute. Although the
+	  104-QUAD-8 counters have a 25-bit range, only the lower 24 bits may be
+	  set, either directly or via the counter's preset attribute. Interrupts
+	  are not supported by this driver.
+
+	  The base port addresses for the devices may be configured via the base
+	  array module parameter.
+
+endif # COUNTER

index b1464604bdbe..aee0d2ddcf2c 100644
@@ -3,3 +3,5 @@
 #
 
 obj-$(CONFIG_COUNTER) += counter.o
+
+obj-$(CONFIG_104_QUAD_8)	+= 104-quad-8.o

index bf1e559ad7cd..eeb358122cbe 100644
@@ -5,23 +5,6 @@
 
 menu "Counters"
 
-config 104_QUAD_8
-	tristate "ACCES 104-QUAD-8 driver"
-	depends on PC104 && X86
-	select ISA_BUS_API
-	help
-	  Say yes here to build support for the ACCES 104-QUAD-8 quadrature
-	  encoder counter/interface device family (104-QUAD-8, 104-QUAD-4).
-
-	  Performing a write to a counter's IIO_CHAN_INFO_RAW sets the counter and
-	  also clears the counter's respective error flag. Although the counters
-	  have a 25-bit range, only the lower 24 bits may be set, either directly
-	  or via a counter's preset attribute. Interrupts are not supported by
-	  this driver.
-
-	  The base port addresses for the devices may be configured via the base
-	  array module parameter.
-
 config STM32_LPTIMER_CNT
 	tristate "STM32 LP Timer encoder counter driver"
 	depends on MFD_STM32_LPTIMER || COMPILE_TEST

index 1b9a896eb488..93933ba49280 100644
@@ -4,5 +4,4 @@
 
 # When adding new entries keep the list in alphabetical order
 
-obj-$(CONFIG_104_QUAD_8)	+= 104-quad-8.o
 obj-$(CONFIG_STM32_LPTIMER_CNT)	+= stm32-lptimer-cnt.o

new file mode 100644
index 000000000000..2d9fa57af101
@@ -0,0 +1,36 @@
+What:		/sys/bus/counter/devices/counterX/signalY/index_polarity
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Active level of index input Signal Y; irrelevant in
+		non-synchronous load mode.
+
+What:		/sys/bus/counter/devices/counterX/signalY/index_polarity_available
+What:		/sys/bus/counter/devices/counterX/signalY/synchronous_mode_available
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Discrete set of available values for the respective Signal Y
+		configuration are listed in this file.
+
+What:		/sys/bus/counter/devices/counterX/signalY/synchronous_mode
+KernelVersion:	4.19
+Contact:	linux-iio at vger.kernel.org
+Description:
+		Configure the counter associated with Signal Y for
+		non-synchronous or synchronous load mode. Synchronous load mode
+		cannot be selected in non-quadrature (Pulse-Direction) clock
+		mode.
+
+		non-synchronous:
+			A logic low level is the active level at this index
+			input. The index function (as enabled via preset_enable)
+			is performed directly on the active level of the index
+			input.
+
+		synchronous:
+			Intended for interfacing with encoder Index output in
+			quadrature clock mode. The active level is configured
+			via index_polarity. The index function (as enabled via
+			preset_enable) is performed synchronously with the
+			quadrature clock on the active level of the index input.

index f41c45246e2b..865c47a3feae 100644
@@ -270,6 +270,7 @@ ACCES 104-QUAD-8 DRIVER
 M:	William Breathitt Gray <[email protected]>
 L:	linux-iio at vger.kernel.org
 S:	Maintained
+F:	Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
 F:	Documentation/ABI/testing/sysfs-bus-iio-counter-104-quad-8
 F:	drivers/counter/104-quad-8.c
 

index dd3add729529..0bb2340d6087 100644
@@ -28,4 +28,14 @@ config 104_QUAD_8
 	  The base port addresses for the devices may be configured via the base
 	  array module parameter.
 
+config STM32_TIMER_CNT
+	tristate "STM32 Timer encoder counter driver"
+	depends on MFD_STM32_TIMERS || COMPILE_TEST
+	help
+	  Select this option to enable STM32 Timer quadrature encoder
+	  and counter driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called stm32-timer-cnt.
+
 endif # COUNTER

index aee0d2ddcf2c..6b4a5be21b00 100644
@@ -5,3 +5,4 @@
 obj-$(CONFIG_COUNTER) += counter.o
 
 obj-$(CONFIG_104_QUAD_8)	+= 104-quad-8.o
+obj-$(CONFIG_STM32_TIMER_CNT)	+= stm32-timer-cnt.o

new file mode 100644
index 000000000000..c52fcdd4bf6c
@@ -0,0 +1,31 @@
+STMicroelectronics STM32 Timer quadrature encoder
+
+STM32 Timer provides quadrature encoder to detect
+angular position and direction of rotary elements,
+from IN1 and IN2 input signals.
+
+Must be a sub-node of an STM32 Timer device tree node.
+See ../mfd/stm32-timers.txt for details about the parent node.
+
+Required properties:
+- compatible:		Must be "st,stm32-timer-counter".
+- pinctrl-names: 	Set to "default".
+- pinctrl-0: 		List of phandles pointing to pin configuration nodes,
+			to set CH1/CH2 pins in mode of operation for STM32
+			Timer input on external pin.
+
+Example:
+	timers at 40010000 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "st,stm32-timers";
+		reg = <0x40010000 0x400>;
+		clocks = <&rcc 0 160>;
+		clock-names = "int";
+
+		counter {
+			compatible = "st,stm32-timer-counter";
+			pinctrl-names = "default";
+			pinctrl-0 = <&tim1_in_pins>;
+		};
+	};

index 0e900b52e895..15c3b87f51d9 100644
@@ -28,6 +28,7 @@ Optional parameters:
 Optional subnodes:
 - pwm:			See ../pwm/pwm-stm32.txt
 - timer:		See ../iio/timer/stm32-timer-trigger.txt
+- counter:		See ../counter/stm32-timer-cnt.txt
 
 Example:
 	timers at 40010000 {

@@ -48,6 +49,12 @@ Example:
 			compatible = "st,stm32-timer-trigger";
 			reg = <0>;
 		};
+
+		counter {
+			compatible = "st,stm32-timer-counter";
+			pinctrl-names = "default";
+			pinctrl-0 = <&tim1_in_pins>;
+		};
 	};
 
 Example with all dmas:

index 0bb2340d6087..87c491a19c63 100644
@@ -38,4 +38,14 @@ config STM32_TIMER_CNT
 	  To compile this driver as a module, choose M here: the
 	  module will be called stm32-timer-cnt.
 
+config STM32_LPTIMER_CNT
+	tristate "STM32 LP Timer encoder counter driver"
+	depends on (MFD_STM32_LPTIMER || COMPILE_TEST) && IIO
+	help
+	  Select this option to enable STM32 Low-Power Timer quadrature encoder
+	  and counter driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called stm32-lptimer-cnt.
+
 endif # COUNTER

index 6b4a5be21b00..5589976d37f8 100644
@@ -6,3 +6,4 @@ obj-$(CONFIG_COUNTER) += counter.o
 
 obj-$(CONFIG_104_QUAD_8)	+= 104-quad-8.o
 obj-$(CONFIG_STM32_TIMER_CNT)	+= stm32-timer-cnt.o
+obj-$(CONFIG_STM32_LPTIMER_CNT)	+= stm32-lptimer-cnt.o

index d08aeb41cd07..ac764840483a 100644
@@ -74,7 +74,6 @@ source "drivers/iio/afe/Kconfig"
 source "drivers/iio/amplifiers/Kconfig"
 source "drivers/iio/chemical/Kconfig"
 source "drivers/iio/common/Kconfig"
-source "drivers/iio/counter/Kconfig"
 source "drivers/iio/dac/Kconfig"
 source "drivers/iio/dummy/Kconfig"
 source "drivers/iio/frequency/Kconfig"

index cb5993251381..bff682ad1cfb 100644
@@ -20,7 +20,6 @@ obj-y += amplifiers/
 obj-y += buffer/
 obj-y += chemical/
 obj-y += common/
-obj-y += counter/
 obj-y += dac/
 obj-y += dummy/
 obj-y += gyro/

deleted file mode 100644
index eeb358122cbe..000000000000
@@ -1,17 +0,0 @@
-#
-# Counter devices
-#
-# When adding new entries keep the list in alphabetical order
-
-menu "Counters"
-
-config STM32_LPTIMER_CNT
-	tristate "STM32 LP Timer encoder counter driver"
-	depends on MFD_STM32_LPTIMER || COMPILE_TEST
-	help
-	  Select this option to enable STM32 Low-Power Timer quadrature encoder
-	  and counter driver.
-
-	  To compile this driver as a module, choose M here: the
-	  module will be called stm32-lptimer-cnt.
-endmenu

deleted file mode 100644
index 93933ba49280..000000000000
@@ -1,7 +0,0 @@
-#
-# Makefile for IIO counter devices
-#
-
-# When adding new entries keep the list in alphabetical order
-
-obj-$(CONFIG_STM32_LPTIMER_CNT)	+= stm32-lptimer-cnt.o

similarity index 100%
rename from Documentation/devicetree/bindings/iio/counter/stm32-lptimer-cnt.txt
rename to Documentation/devicetree/bindings/counter/stm32-lptimer-cnt.txt

index 2a9ff29db9c9..fb54e4dad5b3 100644
@@ -16,7 +16,7 @@ Required properties:
 
 Optional subnodes:
 - pwm:			See ../pwm/pwm-stm32-lp.txt
-- counter:		See ../iio/timer/stm32-lptimer-cnt.txt
+- counter:		See ../counter/stm32-lptimer-cnt.txt
 - trigger:		See ../iio/timer/stm32-lptimer-trigger.txt
 
 Example:

index a5b4f223641d..06218a5ae10c 100644
@@ -1652,6 +1652,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_countY_raw
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Raw counter device counts from channel Y. For quadrature
 		counters, multiplication by an available [Y]_scale results in
 		the counts of a single quadrature signal phase from channel Y.

@@ -1660,6 +1662,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_indexY_raw
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Raw counter device index value from channel Y. This attribute
 		provides an absolute positional reference (e.g. a pulse once per
 		revolution) which may be used to home positional systems as

@@ -1669,6 +1673,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_count_count_direction_available
 KernelVersion:	4.12
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		A list of possible counting directions which are:
 		- "up"	: counter device is increasing.
 		- "down": counter device is decreasing.

@@ -1677,6 +1683,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_countY_count_direction
 KernelVersion:	4.12
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Raw counter device counters direction for channel Y.
 
 What:		/sys/bus/iio/devices/iio:deviceX/in_phaseY_raw

index 7fac2c268d9a..bac3d0d48b7b 100644
@@ -6,6 +6,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_index_synchronous_mode_available
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Discrete set of available values for the respective counter
 		configuration are listed in this file.
 

@@ -13,6 +15,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_countY_count_mode
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Count mode for channel Y. Four count modes are available:
 		normal, range limit, non-recycle, and modulo-n. The preset value
 		for channel Y is used by the count mode where required.

@@ -47,6 +51,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_countY_noise_error
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Read-only attribute that indicates whether excessive noise is
 		present at the channel Y count inputs in quadrature clock mode;
 		irrelevant in non-quadrature clock mode.

@@ -55,6 +61,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_countY_preset
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		If the counter device supports preset registers, the preset
 		count for channel Y is provided by this attribute.
 

@@ -62,6 +70,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_countY_quadrature_mode
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Configure channel Y counter for non-quadrature or quadrature
 		clock mode. Selecting non-quadrature clock mode will disable
 		synchronous load mode. In quadrature clock mode, the channel Y

@@ -83,6 +93,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_countY_set_to_preset_on_index
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Whether to set channel Y counter with channel Y preset value
 		when channel Y index input is active, or continuously count.
 		Valid attribute values are boolean.

@@ -91,6 +103,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_indexY_index_polarity
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Active level of channel Y index input; irrelevant in
 		non-synchronous load mode.
 

@@ -98,6 +112,8 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_indexY_synchronous_mode
 KernelVersion:	4.10
 Contact:	linux-iio at vger.kernel.org
 Description:
+		This interface is deprecated; please use the Counter subsystem.
+
 		Configure channel Y counter for non-synchronous or synchronous
 		load mode. Synchronous load mode cannot be selected in
 		non-quadrature clock mode.