counter: Add support for Intel Quadrature Encoder Peripheral

Add support for Intel Quadrature Encoder Peripheral found on Intel
Elkhart Lake platform.

Initial implementation was done by Felipe Balbi while he was working at
Intel with later changes from Raymond Tan and me.
Co-developed-by: Felipe Balbi (Intel) <balbi@kernel.org>
Signed-off-by: Felipe Balbi (Intel) <balbi@kernel.org>
Co-developed-by: Raymond Tan <raymond.tan@intel.com>
Signed-off-by: Raymond Tan <raymond.tan@intel.com>
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/20210602113259.158674-1-jarkko.nikula@linux.intel.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-counter

@@ -193,6 +193,15 @@ Description:
 		both edges:
 			Any state transition.
 
+What:		/sys/bus/counter/devices/counterX/countY/spike_filter_ns
+KernelVersion:	5.14
+Contact:	linux-iio@vger.kernel.org
+Description:
+		If the counter device supports programmable spike filter this
+		attribute indicates the value in nanoseconds where noise pulses
+		shorter or equal to configured value are ignored. Value 0 means
+		filter is disabled.
+
 What:		/sys/bus/counter/devices/counterX/name
 KernelVersion:	5.2
 Contact:	linux-iio@vger.kernel.org

MAINTAINERS

@@ -9364,6 +9364,11 @@ L:	linux-pm@vger.kernel.org
 S:	Supported
 F:	drivers/cpufreq/intel_pstate.c
 
+INTEL QUADRATURE ENCODER PERIPHERAL DRIVER
+M:	Jarkko Nikula <jarkko.nikula@linux.intel.com>
+L:	linux-iio@vger.kernel.org
+F:	drivers/counter/intel-qep.c
+
 INTEL RDMA RNIC DRIVER
 M:	Faisal Latif <faisal.latif@intel.com>
 M:	Shiraz Saleem <shiraz.saleem@intel.com>

drivers/counter/Kconfig

@@ -91,4 +91,14 @@ config MICROCHIP_TCB_CAPTURE
 	  To compile this driver as a module, choose M here: the
 	  module will be called microchip-tcb-capture.
 
+config INTEL_QEP
+	tristate "Intel Quadrature Encoder Peripheral driver"
+	depends on PCI
+	help
+	  Select this option to enable the Intel Quadrature Encoder Peripheral
+	  driver.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called intel-qep.
+
 endif # COUNTER

drivers/counter/Makefile

@@ -12,3 +12,4 @@ obj-$(CONFIG_STM32_LPTIMER_CNT)	+= stm32-lptimer-cnt.o
 obj-$(CONFIG_TI_EQEP)		+= ti-eqep.o
 obj-$(CONFIG_FTM_QUADDEC)	+= ftm-quaddec.o
 obj-$(CONFIG_MICROCHIP_TCB_CAPTURE)	+= microchip-tcb-capture.o
+obj-$(CONFIG_INTEL_QEP)		+= intel-qep.o