staging: comedi: comedi_8254: introduce module for 8254 timer support

A 8254 timer/counter is commonly used on data acquisition boards to provide
the internal pacer clock used to acquire analog input samples. Some boards
also to allow the timers to be used externally.

Currently the 8254 timers are supported by comedi using the 8253.h header
and a number of inline functions. This works for the internal pacer clock
but requires the drivers to implement subdevice code necessary to use the
timers externally.

Introduce a new module to support both the internal pacer clock and the
external counter subdevice. This will allow removing a bunch of duplicated
code in the drivers and standardizes the comedi 8254 timer support.

This implementation is based on the 8253.h inline functions and the various
subdevice functionality in the comedi drivers.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 664 insertions, 0 deletions

diff --git a/drivers/staging/comedi/drivers/comedi_8254.c b/drivers/staging/comedi/drivers/comedi_8254.c
new file mode 100644
index 000000000000..0d5d56b61f60
--- /dev/null
+++ b/drivers/staging/comedi/drivers/comedi_8254.c
@@ -0,0 +1,664 @@
+/*
+ * comedi_8254.c
+ * Generic 8254 timer/counter support
+ * Copyright (C) 2014 H Hartley Sweeten <hsweeten@visionengravers.com>
+ *
+ * Based on 8253.h and various subdevice implementations in comedi drivers.
+ *
+ * COMEDI - Linux Control and Measurement Device Interface
+ * Copyright (C) 2000 David A. Schleef <ds@schleef.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+/*
+ * Module: comedi_8254
+ * Description: Generic 8254 timer/counter support
+ * Author: H Hartley Sweeten <hsweeten@visionengravers.com>
+ * Updated: Thu Jan 8 16:45:45 MST 2015
+ * Status: works
+ *
+ * This module is not used directly by end-users. Rather, it is used by other
+ * drivers to provide support for an 8254 Programmable Interval Timer. These
+ * counters are typically used to generate the pacer clock used for data
+ * acquisition. Some drivers also expose the counters for general purpose use.
+ *
+ * This module provides the following basic functions:
+ *
+ * comedi_8254_init() / comedi_8254_mm_init()
+ *	Initializes this module to access the 8254 registers. The _mm version
+ *	sets up the module for MMIO register access the other for PIO access.
+ *	The pointer returned from these functions is normally stored in the
+ *	comedi_device dev->pacer and will be freed by the comedi core during
+ *	the driver (*detach). If a driver has multiple 8254 devices, they need
+ *	to be stored in the drivers private data and freed when the driver is
+ *	detached.
+ *
+ *	NOTE: The counters are reset by setting them to I8254_MODE0 as part of
+ *	this initialization.
+ *
+ * comedi_8254_set_mode()
+ *	Sets a counters operation mode:
+ *		I8254_MODE0	Interrupt on terminal count
+ *		I8254_MODE1	Hardware retriggerable one-shot
+ *		I8254_MODE2	Rate generator
+ *		I8254_MODE3	Square wave mode
+ *		I8254_MODE4	Software triggered strobe
+ *		I8254_MODE5	Hardware triggered strobe (retriggerable)
+ *
+ *	In addition I8254_BCD and I8254_BINARY specify the counting mode:
+ *		I8254_BCD	BCD counting
+ *		I8254_BINARY	Binary counting
+ *
+ * comedi_8254_write()
+ *	Writes an initial value to a counter.
+ *
+ *	The largest possible initial count is 0; this is equivalent to 2^16
+ *	for binary counting and 10^4 for BCD counting.
+ *
+ *	NOTE: The counter does not stop when it reaches zero. In Mode 0, 1, 4,
+ *	and 5 the counter "wraps around" to the highest count, either 0xffff
+ *	for binary counting or 9999 for BCD counting, and continues counting.
+ *	Modes 2 and 3 are periodic; the counter reloads itself with the initial
+ *	count and continues counting from there.
+ *
+ * comedi_8254_read()
+ *	Reads the current value from a counter.
+ *
+ * comedi_8254_status()
+ *	Reads the status of a counter.
+ *
+ * comedi_8254_load()
+ *	Sets a counters operation mode and writes the initial value.
+ *
+ * Typically the pacer clock is created by cascading two of the 16-bit counters
+ * to create a 32-bit rate generator (I8254_MODE2). These functions are
+ * provided to handle the cascaded counters:
+ *
+ * comedi_8254_ns_to_timer()
+ *	Calculates the divisor value needed for a single counter to generate
+ *	ns timing.
+ *
+ * comedi_8254_cascade_ns_to_timer()
+ *	Calculates the two divisor values needed to the generate the pacer
+ *	clock (in ns).
+ *
+ * comedi_8254_update_divisors()
+ *	Transfers the intermediate divisor values to the current divisors.
+ *
+ * comedi_8254_pacer_enable()
+ *	Programs the mode of the cascaded counters and writes the current
+ *	divisor values.
+ *
+ * To expose the counters as a subdevice for general purpose use the following
+ * functions a provided:
+ *
+ * comedi_8254_subdevice_init()
+ *	Initializes a comedi_subdevice to use the 8254 timer.
+ *
+ * comedi_8254_set_busy()
+ *	Internally flags a counter as "busy". This is done to protect the
+ *	counters that are used for the cascaded 32-bit pacer.
+ *
+ * The subdevice provides (*insn_read) and (*insn_write) operations to read
+ * the current value and write an initial value to a counter. A (*insn_config)
+ * operation is also provided to handle the following comedi instructions:
+ *
+ *	INSN_CONFIG_SET_COUNTER_MODE	calls comedi_8254_set_mode()
+ *	INSN_CONFIG_8254_READ_STATUS	calls comedi_8254_status()
+ *
+ * The (*insn_config) member of comedi_8254 can be initialized by the external
+ * driver to handle any additional instructions.
+ *
+ * NOTE: Gate control, clock routing, and any interrupt handling for the
+ * counters is not handled by this module. These features are driver dependent.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/io.h>
+
+#include "../comedidev.h"
+
+#include "comedi_8254.h"
+
+static unsigned int __i8254_read(struct comedi_8254 *i8254, unsigned int reg)
+{
+	unsigned int reg_offset = (reg * i8254->iosize) << i8254->regshift;
+	unsigned int val;
+
+	switch (i8254->iosize) {
+	default:
+	case I8254_IO8:
+		if (i8254->mmio)
+			val = readb(i8254->mmio + reg_offset);
+		else
+			val = inb(i8254->iobase + reg_offset);
+		break;
+	case I8254_IO16:
+		if (i8254->mmio)
+			val = readw(i8254->mmio + reg_offset);
+		else
+			val = inw(i8254->iobase + reg_offset);
+		break;
+	case I8254_IO32:
+		if (i8254->mmio)
+			val = readl(i8254->mmio + reg_offset);
+		else
+			val = inl(i8254->iobase + reg_offset);
+		break;
+	}
+	return val & 0xff;
+}
+
+static void __i8254_write(struct comedi_8254 *i8254,
+			  unsigned int val, unsigned int reg)
+{
+	unsigned int reg_offset = (reg * i8254->iosize) << i8254->regshift;
+
+	switch (i8254->iosize) {
+	default:
+	case I8254_IO8:
+		if (i8254->mmio)
+			writeb(val, i8254->mmio + reg_offset);
+		else
+			outb(val, i8254->iobase + reg_offset);
+		break;
+	case I8254_IO16:
+		if (i8254->mmio)
+			writew(val, i8254->mmio + reg_offset);
+		else
+			outw(val, i8254->iobase + reg_offset);
+		break;
+	case I8254_IO32:
+		if (i8254->mmio)
+			writel(val, i8254->mmio + reg_offset);
+		else
+			outl(val, i8254->iobase + reg_offset);
+		break;
+	}
+}
+
+/**
+ * comedi_8254_status - return the status of a counter
+ * @i8254:	comedi_8254 struct for the timer
+ * @counter:	the counter number
+ */
+unsigned int comedi_8254_status(struct comedi_8254 *i8254, unsigned int counter)
+{
+	unsigned int cmd;
+
+	if (counter > 2)
+		return 0;
+
+	cmd = I8254_CTRL_READBACK_STATUS | I8254_CTRL_READBACK_SEL_CTR(counter);
+	__i8254_write(i8254, cmd, I8254_CTRL_REG);
+
+	return __i8254_read(i8254, counter);
+}
+EXPORT_SYMBOL_GPL(comedi_8254_status);
+
+/**
+ * comedi_8254_read - read the current counter value
+ * @i8254:	comedi_8254 struct for the timer
+ * @counter:	the counter number
+ */
+unsigned int comedi_8254_read(struct comedi_8254 *i8254, unsigned int counter)
+{
+	unsigned int val;
+
+	if (counter > 2)
+		return 0;
+
+	/* latch counter */
+	__i8254_write(i8254, I8254_CTRL_SEL_CTR(counter) | I8254_CTRL_LATCH,
+		      I8254_CTRL_REG);
+
+	/* read LSB then MSB */
+	val = __i8254_read(i8254, counter);
+	val |= (__i8254_read(i8254, counter) << 8);
+
+	return val;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_read);
+
+/**
+ * comedi_8254_write - load a 16-bit initial counter value
+ * @i8254:	comedi_8254 struct for the timer
+ * @counter:	the counter number
+ * @val:	the initial value
+ */
+void comedi_8254_write(struct comedi_8254 *i8254,
+		       unsigned int counter, unsigned int val)
+{
+	unsigned int byte;
+
+	if (counter > 2)
+		return;
+	if (val > 0xffff)
+		return;
+
+	/* load LSB then MSB */
+	byte = val & 0xff;
+	__i8254_write(i8254, byte, counter);
+	byte = (val >> 8) & 0xff;
+	__i8254_write(i8254, byte, counter);
+}
+EXPORT_SYMBOL_GPL(comedi_8254_write);
+
+/**
+ * comedi_8254_set_mode - set the mode of a counter
+ * @i8254:	comedi_8254 struct for the timer
+ * @counter:	the counter number
+ * @mode:	the I8254_MODEx and I8254_BCD|I8254_BINARY
+ */
+int comedi_8254_set_mode(struct comedi_8254 *i8254, unsigned int counter,
+			 unsigned int mode)
+{
+	unsigned int byte;
+
+	if (counter > 2)
+		return -EINVAL;
+	if (mode > (I8254_MODE5 | I8254_BCD))
+		return -EINVAL;
+
+	byte = I8254_CTRL_SEL_CTR(counter) |	/* select counter */
+	       I8254_CTRL_LSB_MSB |		/* load LSB then MSB */
+	       mode;				/* mode and BCD|binary */
+	__i8254_write(i8254, byte, I8254_CTRL_REG);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_set_mode);
+
+/**
+ * comedi_8254_load - program the mode and initial count of a counter
+ * @i8254:	comedi_8254 struct for the timer
+ * @counter:	the counter number
+ * @mode:	the I8254_MODEx and I8254_BCD|I8254_BINARY
+ * @val:	the initial value
+ */
+int comedi_8254_load(struct comedi_8254 *i8254, unsigned int counter,
+		     unsigned int val, unsigned int mode)
+{
+	if (counter > 2)
+		return -EINVAL;
+	if (val > 0xffff)
+		return -EINVAL;
+	if (mode > (I8254_MODE5 | I8254_BCD))
+		return -EINVAL;
+
+	comedi_8254_set_mode(i8254, counter, mode);
+	comedi_8254_write(i8254, counter, val);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_load);
+
+/**
+ * comedi_8254_pacer_enable - set the mode and load the cascaded counters
+ * @i8254:	comedi_8254 struct for the timer
+ * @counter1:	the counter number for the first divisor
+ * @counter2:	the counter number for the second divisor
+ * @enable:	flag to enable (load) the counters
+ */
+void comedi_8254_pacer_enable(struct comedi_8254 *i8254,
+			      unsigned int counter1,
+			      unsigned int counter2,
+			      bool enable)
+{
+	unsigned int mode;
+
+	if (counter1 > 2 || counter2 > 2 || counter1 == counter2)
+		return;
+
+	if (enable)
+		mode = I8254_MODE2 | I8254_BINARY;
+	else
+		mode = I8254_MODE0 | I8254_BINARY;
+
+	comedi_8254_set_mode(i8254, counter1, mode);
+	comedi_8254_set_mode(i8254, counter2, mode);
+
+	if (enable) {
+		/*
+		 * Divisors are loaded second counter then first counter to
+		 * avoid possible issues with the first counter expiring
+		 * before the second counter is loaded.
+		 */
+		comedi_8254_write(i8254, counter2, i8254->divisor2);
+		comedi_8254_write(i8254, counter1, i8254->divisor1);
+	}
+}
+EXPORT_SYMBOL_GPL(comedi_8254_pacer_enable);
+
+/**
+ * comedi_8254_update_divisors - update the divisors for the cascaded counters
+ * @i8254:	comedi_8254 struct for the timer
+ */
+void comedi_8254_update_divisors(struct comedi_8254 *i8254)
+{
+	/* masking is done since counter maps zero to 0x10000 */
+	i8254->divisor = i8254->next_div & 0xffff;
+	i8254->divisor1 = i8254->next_div1 & 0xffff;
+	i8254->divisor2 = i8254->next_div2 & 0xffff;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_update_divisors);
+
+/**
+ * comedi_8254_cascade_ns_to_timer - calculate the cascaded divisor values
+ * @i8254:	comedi_8254 struct for the timer
+ * @nanosec:	the desired ns time
+ * @flags:	comedi_cmd flags
+ */
+void comedi_8254_cascade_ns_to_timer(struct comedi_8254 *i8254,
+				     unsigned int *nanosec,
+				     unsigned int flags)
+{
+	unsigned int d1 = i8254->next_div1 ? i8254->next_div1 : I8254_MAX_COUNT;
+	unsigned int d2 = i8254->next_div2 ? i8254->next_div2 : I8254_MAX_COUNT;
+	unsigned int div = d1 * d2;
+	unsigned int ns_lub = 0xffffffff;
+	unsigned int ns_glb = 0;
+	unsigned int d1_lub = 0;
+	unsigned int d1_glb = 0;
+	unsigned int d2_lub = 0;
+	unsigned int d2_glb = 0;
+	unsigned int start;
+	unsigned int ns;
+	unsigned int ns_low;
+	unsigned int ns_high;
+
+	/* exit early if everything is already correct */
+	if (div * i8254->osc_base == *nanosec &&
+	    d1 > 1 && d1 <= I8254_MAX_COUNT &&
+	    d2 > 1 && d2 <= I8254_MAX_COUNT &&
+	    /* check for overflow */
+	    div > d1 && div > d2 &&
+	    div * i8254->osc_base > div &&
+	    div * i8254->osc_base > i8254->osc_base)
+		return;
+
+	div = *nanosec / i8254->osc_base;
+	d2 = I8254_MAX_COUNT;
+	start = div / d2;
+	if (start < 2)
+		start = 2;
+	for (d1 = start; d1 <= div / d1 + 1 && d1 <= I8254_MAX_COUNT; d1++) {
+		for (d2 = div / d1;
+		     d1 * d2 <= div + d1 + 1 && d2 <= I8254_MAX_COUNT; d2++) {
+			ns = i8254->osc_base * d1 * d2;
+			if (ns <= *nanosec && ns > ns_glb) {
+				ns_glb = ns;
+				d1_glb = d1;
+				d2_glb = d2;
+			}
+			if (ns >= *nanosec && ns < ns_lub) {
+				ns_lub = ns;
+				d1_lub = d1;
+				d2_lub = d2;
+			}
+		}
+	}
+
+	switch (flags & CMDF_ROUND_MASK) {
+	case CMDF_ROUND_NEAREST:
+	default:
+		ns_high = d1_lub * d2_lub * i8254->osc_base;
+		ns_low = d1_glb * d2_glb * i8254->osc_base;
+		if (ns_high - *nanosec < *nanosec - ns_low) {
+			d1 = d1_lub;
+			d2 = d2_lub;
+		} else {
+			d1 = d1_glb;
+			d2 = d2_glb;
+		}
+		break;
+	case CMDF_ROUND_UP:
+		d1 = d1_lub;
+		d2 = d2_lub;
+		break;
+	case CMDF_ROUND_DOWN:
+		d1 = d1_glb;
+		d2 = d2_glb;
+		break;
+	}
+
+	*nanosec = d1 * d2 * i8254->osc_base;
+	i8254->next_div1 = d1;
+	i8254->next_div2 = d2;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_cascade_ns_to_timer);
+
+/**
+ * comedi_8254_ns_to_timer - calculate the divisor value for nanosec timing
+ * @i8254:	comedi_8254 struct for the timer
+ * @nanosec:	the desired ns time
+ * @flags:	comedi_cmd flags
+ */
+void comedi_8254_ns_to_timer(struct comedi_8254 *i8254,
+			     unsigned int *nanosec, unsigned int flags)
+{
+	unsigned int divisor;
+
+	switch (flags & CMDF_ROUND_MASK) {
+	default:
+	case CMDF_ROUND_NEAREST:
+		divisor = DIV_ROUND_CLOSEST(*nanosec, i8254->osc_base);
+		break;
+	case CMDF_ROUND_UP:
+		divisor = DIV_ROUND_UP(*nanosec, i8254->osc_base);
+		break;
+	case CMDF_ROUND_DOWN:
+		divisor = *nanosec / i8254->osc_base;
+		break;
+	}
+	if (divisor < 2)
+		divisor = 2;
+	if (divisor > I8254_MAX_COUNT)
+		divisor = I8254_MAX_COUNT;
+
+	*nanosec = divisor * i8254->osc_base;
+	i8254->next_div = divisor;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_ns_to_timer);
+
+/**
+ * comedi_8254_set_busy - set/clear the "busy" flag for a given counter
+ * @i8254:	comedi_8254 struct for the timer
+ * @counter:	the counter number
+ * @busy:	set/clear flag
+ */
+void comedi_8254_set_busy(struct comedi_8254 *i8254,
+			  unsigned int counter, bool busy)
+{
+	if (counter < 3)
+		i8254->busy[counter] = busy;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_set_busy);
+
+static int comedi_8254_insn_read(struct comedi_device *dev,
+				 struct comedi_subdevice *s,
+				 struct comedi_insn *insn,
+				 unsigned int *data)
+{
+	struct comedi_8254 *i8254 = s->private;
+	unsigned int chan = CR_CHAN(insn->chanspec);
+	int i;
+
+	if (i8254->busy[chan])
+		return -EBUSY;
+
+	for (i = 0; i < insn->n; i++)
+		data[i] = comedi_8254_read(i8254, chan);
+
+	return insn->n;
+}
+
+static int comedi_8254_insn_write(struct comedi_device *dev,
+				  struct comedi_subdevice *s,
+				  struct comedi_insn *insn,
+				  unsigned int *data)
+{
+	struct comedi_8254 *i8254 = s->private;
+	unsigned int chan = CR_CHAN(insn->chanspec);
+
+	if (i8254->busy[chan])
+		return -EBUSY;
+
+	if (insn->n)
+		comedi_8254_write(i8254, chan, data[insn->n - 1]);
+
+	return insn->n;
+}
+
+static int comedi_8254_insn_config(struct comedi_device *dev,
+				   struct comedi_subdevice *s,
+				   struct comedi_insn *insn,
+				   unsigned int *data)
+{
+	struct comedi_8254 *i8254 = s->private;
+	unsigned int chan = CR_CHAN(insn->chanspec);
+	int ret;
+
+	if (i8254->busy[chan])
+		return -EBUSY;
+
+	switch (data[0]) {
+	case INSN_CONFIG_RESET:
+		ret = comedi_8254_set_mode(i8254, chan,
+					   I8254_MODE0 | I8254_BINARY);
+		if (ret)
+			return ret;
+		break;
+	case INSN_CONFIG_SET_COUNTER_MODE:
+		ret = comedi_8254_set_mode(i8254, chan, data[1]);
+		if (ret)
+			return ret;
+		break;
+	case INSN_CONFIG_8254_READ_STATUS:
+		data[1] = comedi_8254_status(i8254, chan);
+		break;
+	default:
+		/*
+		 * If available, call the driver provided (*insn_config)
+		 * to handle any driver implemented instructions.
+		 */
+		if (i8254->insn_config)
+			return i8254->insn_config(dev, s, insn, data);
+
+		return -EINVAL;
+	}
+
+	return insn->n;
+}
+
+/**
+ * comedi_8254_subdevice_init - initialize a comedi_subdevice for the 8254 timer
+ * @s:		comedi_subdevice struct
+ */
+void comedi_8254_subdevice_init(struct comedi_subdevice *s,
+				struct comedi_8254 *i8254)
+{
+	s->type		= COMEDI_SUBD_COUNTER;
+	s->subdev_flags	= SDF_READABLE | SDF_WRITABLE;
+	s->n_chan	= 3;
+	s->maxdata	= 0xffff;
+	s->range_table	= &range_unknown;
+	s->insn_read	= comedi_8254_insn_read;
+	s->insn_write	= comedi_8254_insn_write;
+	s->insn_config	= comedi_8254_insn_config;
+
+	s->private	= i8254;
+}
+EXPORT_SYMBOL_GPL(comedi_8254_subdevice_init);
+
+static struct comedi_8254 *__i8254_init(unsigned long iobase,
+					void __iomem *mmio,
+					unsigned int osc_base,
+					unsigned int iosize,
+					unsigned int regshift)
+{
+	struct comedi_8254 *i8254;
+	int i;
+
+	/* sanity check that the iosize is valid */
+	if (!(iosize == I8254_IO8 || iosize == I8254_IO16 ||
+	      iosize == I8254_IO32))
+		return NULL;
+
+	i8254 = kzalloc(sizeof(*i8254), GFP_KERNEL);
+	if (!i8254)
+		return NULL;
+
+	i8254->iobase	= iobase;
+	i8254->mmio	= mmio;
+	i8254->iosize	= iosize;
+	i8254->regshift	= regshift;
+
+	/* default osc_base to the max speed of a generic 8254 timer */
+	i8254->osc_base	= osc_base ? osc_base : I8254_OSC_BASE_10MHZ;
+
+	/* reset all the counters by setting them to I8254_MODE0 */
+	for (i = 0; i < 3; i++)
+		comedi_8254_set_mode(i8254, i, I8254_MODE0 | I8254_BINARY);
+
+	return i8254;
+}
+
+/**
+ * comedi_8254_init - allocate and initialize the 8254 device for pio access
+ * @mmio:	port I/O base address
+ * @osc_base:	base time of the counter in ns
+ *		OPTIONAL - only used by comedi_8254_cascade_ns_to_timer()
+ * @iosize:	I/O register size
+ * @regshift:	register gap shift
+ */
+struct comedi_8254 *comedi_8254_init(unsigned long iobase,
+				     unsigned int osc_base,
+				     unsigned int iosize,
+				     unsigned int regshift)
+{
+	return __i8254_init(iobase, NULL, osc_base, iosize, regshift);
+}
+EXPORT_SYMBOL_GPL(comedi_8254_init);
+
+/**
+ * comedi_8254_mm_init - allocate and initialize the 8254 device for mmio access
+ * @mmio:	memory mapped I/O base address
+ * @osc_base:	base time of the counter in ns
+ *		OPTIONAL - only used by comedi_8254_cascade_ns_to_timer()
+ * @iosize:	I/O register size
+ * @regshift:	register gap shift
+ */
+struct comedi_8254 *comedi_8254_mm_init(void __iomem *mmio,
+					unsigned int osc_base,
+					unsigned int iosize,
+					unsigned int regshift)
+{
+	return __i8254_init(0, mmio, osc_base, iosize, regshift);
+}
+EXPORT_SYMBOL_GPL(comedi_8254_mm_init);
+
+static int __init comedi_8254_module_init(void)
+{
+	return 0;
+}
+module_init(comedi_8254_module_init);
+
+static void __exit comedi_8254_module_exit(void)
+{
+}
+module_exit(comedi_8254_module_exit);
+
+MODULE_AUTHOR("H Hartley Sweeten <hsweeten@visionengravers.com>");
+MODULE_DESCRIPTION("Comedi: Generic 8254 timer/counter support");
+MODULE_LICENSE("GPL");