counter: i8254: Introduce the Intel 8254 interface library module

Exposes consumer library functions providing support for interfaces
compatible with the venerable Intel 8254 Programmable Interval Timer
(PIT).

The Intel 8254 PIT first appeared in the early 1980s and was used
initially in IBM PC compatibles. The popularity of the original Intel
825x family of chips led to many subsequent variants and clones of the
interface in various chips and integrated circuits. Although still
popular, interfaces compatible with the Intel 8254 PIT are nowdays
typically found embedded in larger VLSI processing chips and FPGA
components rather than as discrete ICs.

A CONFIG_I8254 Kconfig option is introduced by this patch. Modules
wanting access to these i8254 library functions should select this
Kconfig option, and import the I8254 symbol namespace.

Link: https://lore.kernel.org/r/f6fe32c2db9525d816ab1a01f45abad56c081652.1681665189.git.william.gray@linaro.org/
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>

4 files changed, 470 insertions, 1 deletions

diff --git a/drivers/counter/Kconfig b/drivers/counter/Kconfig
index f8b2a6508bb3..a61a4b9b8ec6 100644
--- a/drivers/counter/Kconfig
+++ b/drivers/counter/Kconfig
@@ -10,6 +10,21 @@ menuconfig COUNTER
 	  interface. You only need to enable this, if you also want to enable
 	  one or more of the counter device drivers below.
 
+config I8254
+	tristate
+	select COUNTER
+	select REGMAP
+	help
+	  Enables support for the i8254 interface library functions. The i8254
+	  interface library provides functions to facilitate communication with
+	  interfaces compatible with the venerable Intel 8254 Programmable
+	  Interval Timer (PIT). The Intel 825x family of chips was first
+	  released in the early 1980s but compatible interfaces are nowadays
+	  typically found embedded in larger VLSI processing chips and FPGA
+	  components.
+
+	  If built as a module its name will be i8254.
+
 if COUNTER
 
 config 104_QUAD_8
diff --git a/drivers/counter/Makefile b/drivers/counter/Makefile
index 933fdd50b3e4..fa3c1d08f706 100644
--- a/drivers/counter/Makefile
+++ b/drivers/counter/Makefile
@@ -6,6 +6,7 @@
 obj-$(CONFIG_COUNTER) += counter.o
 counter-y := counter-core.o counter-sysfs.o counter-chrdev.o
 
+obj-$(CONFIG_I8254)		+= i8254.o
 obj-$(CONFIG_104_QUAD_8)	+= 104-quad-8.o
 obj-$(CONFIG_INTERRUPT_CNT)		+= interrupt-cnt.o
 obj-$(CONFIG_RZ_MTU3_CNT)	+= rz-mtu3-cnt.o
diff --git a/drivers/counter/counter-sysfs.c b/drivers/counter/counter-sysfs.c
index b9efe66f9f8d..42c523343d32 100644
--- a/drivers/counter/counter-sysfs.c
+++ b/drivers/counter/counter-sysfs.c
@@ -88,7 +88,13 @@ static const char *const counter_count_mode_str[] = {
 	[COUNTER_COUNT_MODE_NORMAL] = "normal",
 	[COUNTER_COUNT_MODE_RANGE_LIMIT] = "range limit",
 	[COUNTER_COUNT_MODE_NON_RECYCLE] = "non-recycle",
-	[COUNTER_COUNT_MODE_MODULO_N] = "modulo-n"
+	[COUNTER_COUNT_MODE_MODULO_N] = "modulo-n",
+	[COUNTER_COUNT_MODE_INTERRUPT_ON_TERMINAL_COUNT] = "interrupt on terminal count",
+	[COUNTER_COUNT_MODE_HARDWARE_RETRIGGERABLE_ONESHOT] = "hardware retriggerable one-shot",
+	[COUNTER_COUNT_MODE_RATE_GENERATOR] = "rate generator",
+	[COUNTER_COUNT_MODE_SQUARE_WAVE_MODE] = "square wave mode",
+	[COUNTER_COUNT_MODE_SOFTWARE_TRIGGERED_STROBE] = "software triggered strobe",
+	[COUNTER_COUNT_MODE_HARDWARE_TRIGGERED_STROBE] = "hardware triggered strobe",
 };
 
 static const char *const counter_signal_polarity_str[] = {
diff --git a/drivers/counter/i8254.c b/drivers/counter/i8254.c
new file mode 100644
index 000000000000..c41e4fdc9601
--- /dev/null
+++ b/drivers/counter/i8254.c
@@ -0,0 +1,447 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Intel 8254 Programmable Interval Timer
+ * Copyright (C) William Breathitt Gray
+ */
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/counter.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/i8254.h>
+#include <linux/limits.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/regmap.h>
+
+#include <asm/unaligned.h>
+
+#define I8254_COUNTER_REG(_counter) (_counter)
+#define I8254_CONTROL_REG 0x3
+
+#define I8254_SC GENMASK(7, 6)
+#define I8254_RW GENMASK(5, 4)
+#define I8254_M GENMASK(3, 1)
+#define I8254_CONTROL(_sc, _rw, _m) \
+	(u8_encode_bits(_sc, I8254_SC) | u8_encode_bits(_rw, I8254_RW) | \
+	 u8_encode_bits(_m, I8254_M))
+
+#define I8254_RW_TWO_BYTE 0x3
+#define I8254_MODE_INTERRUPT_ON_TERMINAL_COUNT 0
+#define I8254_MODE_HARDWARE_RETRIGGERABLE_ONESHOT 1
+#define I8254_MODE_RATE_GENERATOR 2
+#define I8254_MODE_SQUARE_WAVE_MODE 3
+#define I8254_MODE_SOFTWARE_TRIGGERED_STROBE 4
+#define I8254_MODE_HARDWARE_TRIGGERED_STROBE 5
+
+#define I8254_COUNTER_LATCH(_counter) I8254_CONTROL(_counter, 0x0, 0x0)
+#define I8254_PROGRAM_COUNTER(_counter, _mode) I8254_CONTROL(_counter, I8254_RW_TWO_BYTE, _mode)
+
+#define I8254_NUM_COUNTERS 3
+
+/**
+ * struct i8254 - I8254 device private data structure
+ * @lock:	synchronization lock to prevent I/O race conditions
+ * @preset:	array of Counter Register states
+ * @out_mode:	array of mode configuration states
+ * @map:	Regmap for the device
+ */
+struct i8254 {
+	struct mutex lock;
+	u16 preset[I8254_NUM_COUNTERS];
+	u8 out_mode[I8254_NUM_COUNTERS];
+	struct regmap *map;
+};
+
+static int i8254_count_read(struct counter_device *const counter, struct counter_count *const count,
+			    u64 *const val)
+{
+	struct i8254 *const priv = counter_priv(counter);
+	int ret;
+	u8 value[2];
+
+	mutex_lock(&priv->lock);
+
+	ret = regmap_write(priv->map, I8254_CONTROL_REG, I8254_COUNTER_LATCH(count->id));
+	if (ret) {
+		mutex_unlock(&priv->lock);
+		return ret;
+	}
+	ret = regmap_noinc_read(priv->map, I8254_COUNTER_REG(count->id), value, sizeof(value));
+	if (ret) {
+		mutex_unlock(&priv->lock);
+		return ret;
+	}
+
+	mutex_unlock(&priv->lock);
+
+	*val = get_unaligned_le16(value);
+
+	return ret;
+}
+
+static int i8254_function_read(struct counter_device *const counter,
+			       struct counter_count *const count,
+			       enum counter_function *const function)
+{
+	*function = COUNTER_FUNCTION_DECREASE;
+	return 0;
+}
+
+#define I8254_SYNAPSES_PER_COUNT 2
+#define I8254_SIGNAL_ID_CLK 0
+#define I8254_SIGNAL_ID_GATE 1
+
+static int i8254_action_read(struct counter_device *const counter,
+			     struct counter_count *const count,
+			     struct counter_synapse *const synapse,
+			     enum counter_synapse_action *const action)
+{
+	struct i8254 *const priv = counter_priv(counter);
+
+	switch (synapse->signal->id % I8254_SYNAPSES_PER_COUNT) {
+	case I8254_SIGNAL_ID_CLK:
+		*action = COUNTER_SYNAPSE_ACTION_FALLING_EDGE;
+		return 0;
+	case I8254_SIGNAL_ID_GATE:
+		switch (priv->out_mode[count->id]) {
+		case I8254_MODE_HARDWARE_RETRIGGERABLE_ONESHOT:
+		case I8254_MODE_RATE_GENERATOR:
+		case I8254_MODE_SQUARE_WAVE_MODE:
+		case I8254_MODE_HARDWARE_TRIGGERED_STROBE:
+			*action = COUNTER_SYNAPSE_ACTION_RISING_EDGE;
+			return 0;
+		default:
+			*action = COUNTER_SYNAPSE_ACTION_NONE;
+			return 0;
+		}
+	default:
+		/* should never reach this path */
+		return -EINVAL;
+	}
+}
+
+static int i8254_count_ceiling_read(struct counter_device *const counter,
+				    struct counter_count *const count, u64 *const ceiling)
+{
+	struct i8254 *const priv = counter_priv(counter);
+
+	mutex_lock(&priv->lock);
+
+	switch (priv->out_mode[count->id]) {
+	case I8254_MODE_RATE_GENERATOR:
+		/* Rate Generator decrements 0 by one and the counter "wraps around" */
+		*ceiling = (priv->preset[count->id] == 0) ? U16_MAX : priv->preset[count->id];
+		break;
+	case I8254_MODE_SQUARE_WAVE_MODE:
+		if (priv->preset[count->id] % 2)
+			*ceiling = priv->preset[count->id] - 1;
+		else if (priv->preset[count->id] == 0)
+			/* Square Wave Mode decrements 0 by two and the counter "wraps around" */
+			*ceiling = U16_MAX - 1;
+		else
+			*ceiling = priv->preset[count->id];
+		break;
+	default:
+		*ceiling = U16_MAX;
+		break;
+	}
+
+	mutex_unlock(&priv->lock);
+
+	return 0;
+}
+
+static int i8254_count_mode_read(struct counter_device *const counter,
+				 struct counter_count *const count,
+				 enum counter_count_mode *const count_mode)
+{
+	const struct i8254 *const priv = counter_priv(counter);
+
+	switch (priv->out_mode[count->id]) {
+	case I8254_MODE_INTERRUPT_ON_TERMINAL_COUNT:
+		*count_mode = COUNTER_COUNT_MODE_INTERRUPT_ON_TERMINAL_COUNT;
+		return 0;
+	case I8254_MODE_HARDWARE_RETRIGGERABLE_ONESHOT:
+		*count_mode = COUNTER_COUNT_MODE_HARDWARE_RETRIGGERABLE_ONESHOT;
+		return 0;
+	case I8254_MODE_RATE_GENERATOR:
+		*count_mode = COUNTER_COUNT_MODE_RATE_GENERATOR;
+		return 0;
+	case I8254_MODE_SQUARE_WAVE_MODE:
+		*count_mode = COUNTER_COUNT_MODE_SQUARE_WAVE_MODE;
+		return 0;
+	case I8254_MODE_SOFTWARE_TRIGGERED_STROBE:
+		*count_mode = COUNTER_COUNT_MODE_SOFTWARE_TRIGGERED_STROBE;
+		return 0;
+	case I8254_MODE_HARDWARE_TRIGGERED_STROBE:
+		*count_mode = COUNTER_COUNT_MODE_HARDWARE_TRIGGERED_STROBE;
+		return 0;
+	default:
+		/* should never reach this path */
+		return -EINVAL;
+	}
+}
+
+static int i8254_count_mode_write(struct counter_device *const counter,
+				  struct counter_count *const count,
+				  const enum counter_count_mode count_mode)
+{
+	struct i8254 *const priv = counter_priv(counter);
+	u8 out_mode;
+	int ret;
+
+	switch (count_mode) {
+	case COUNTER_COUNT_MODE_INTERRUPT_ON_TERMINAL_COUNT:
+		out_mode = I8254_MODE_INTERRUPT_ON_TERMINAL_COUNT;
+		break;
+	case COUNTER_COUNT_MODE_HARDWARE_RETRIGGERABLE_ONESHOT:
+		out_mode = I8254_MODE_HARDWARE_RETRIGGERABLE_ONESHOT;
+		break;
+	case COUNTER_COUNT_MODE_RATE_GENERATOR:
+		out_mode = I8254_MODE_RATE_GENERATOR;
+		break;
+	case COUNTER_COUNT_MODE_SQUARE_WAVE_MODE:
+		out_mode = I8254_MODE_SQUARE_WAVE_MODE;
+		break;
+	case COUNTER_COUNT_MODE_SOFTWARE_TRIGGERED_STROBE:
+		out_mode = I8254_MODE_SOFTWARE_TRIGGERED_STROBE;
+		break;
+	case COUNTER_COUNT_MODE_HARDWARE_TRIGGERED_STROBE:
+		out_mode = I8254_MODE_HARDWARE_TRIGGERED_STROBE;
+		break;
+	default:
+		/* should never reach this path */
+		return -EINVAL;
+	}
+
+	mutex_lock(&priv->lock);
+
+	/* Counter Register is cleared when the counter is programmed */
+	priv->preset[count->id] = 0;
+	priv->out_mode[count->id] = out_mode;
+	ret = regmap_write(priv->map, I8254_CONTROL_REG,
+			   I8254_PROGRAM_COUNTER(count->id, out_mode));
+
+	mutex_unlock(&priv->lock);
+
+	return ret;
+}
+
+static int i8254_count_floor_read(struct counter_device *const counter,
+				  struct counter_count *const count, u64 *const floor)
+{
+	struct i8254 *const priv = counter_priv(counter);
+
+	mutex_lock(&priv->lock);
+
+	switch (priv->out_mode[count->id]) {
+	case I8254_MODE_RATE_GENERATOR:
+		/* counter is always reloaded after 1, but 0 is a possible reload value */
+		*floor = (priv->preset[count->id] == 0) ? 0 : 1;
+		break;
+	case I8254_MODE_SQUARE_WAVE_MODE:
+		/* counter is always reloaded after 2 for even preset values */
+		*floor = (priv->preset[count->id] % 2 || priv->preset[count->id] == 0) ? 0 : 2;
+		break;
+	default:
+		*floor = 0;
+		break;
+	}
+
+	mutex_unlock(&priv->lock);
+
+	return 0;
+}
+
+static int i8254_count_preset_read(struct counter_device *const counter,
+				   struct counter_count *const count, u64 *const preset)
+{
+	const struct i8254 *const priv = counter_priv(counter);
+
+	*preset = priv->preset[count->id];
+
+	return 0;
+}
+
+static int i8254_count_preset_write(struct counter_device *const counter,
+				    struct counter_count *const count, const u64 preset)
+{
+	struct i8254 *const priv = counter_priv(counter);
+	int ret;
+	u8 value[2];
+
+	if (preset > U16_MAX)
+		return -ERANGE;
+
+	mutex_lock(&priv->lock);
+
+	if (priv->out_mode[count->id] == I8254_MODE_RATE_GENERATOR ||
+	    priv->out_mode[count->id] == I8254_MODE_SQUARE_WAVE_MODE) {
+		if (preset == 1) {
+			mutex_unlock(&priv->lock);
+			return -EINVAL;
+		}
+	}
+
+	priv->preset[count->id] = preset;
+
+	put_unaligned_le16(preset, value);
+	ret = regmap_noinc_write(priv->map, I8254_COUNTER_REG(count->id), value, 2);
+
+	mutex_unlock(&priv->lock);
+
+	return ret;
+}
+
+static int i8254_init_hw(struct regmap *const map)
+{
+	unsigned long i;
+	int ret;
+
+	for (i = 0; i < I8254_NUM_COUNTERS; i++) {
+		/* Initialize each counter to Mode 0 */
+		ret = regmap_write(map, I8254_CONTROL_REG,
+				   I8254_PROGRAM_COUNTER(i, I8254_MODE_INTERRUPT_ON_TERMINAL_COUNT));
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static const struct counter_ops i8254_ops = {
+	.count_read = i8254_count_read,
+	.function_read = i8254_function_read,
+	.action_read = i8254_action_read,
+};
+
+#define I8254_SIGNAL(_id, _name) {		\
+	.id = (_id),				\
+	.name = (_name),			\
+}
+
+static struct counter_signal i8254_signals[] = {
+	I8254_SIGNAL(0, "CLK 0"), I8254_SIGNAL(1, "GATE 0"),
+	I8254_SIGNAL(2, "CLK 1"), I8254_SIGNAL(3, "GATE 1"),
+	I8254_SIGNAL(4, "CLK 2"), I8254_SIGNAL(5, "GATE 2"),
+};
+
+static const enum counter_synapse_action i8254_clk_actions[] = {
+	COUNTER_SYNAPSE_ACTION_FALLING_EDGE,
+};
+static const enum counter_synapse_action i8254_gate_actions[] = {
+	COUNTER_SYNAPSE_ACTION_NONE,
+	COUNTER_SYNAPSE_ACTION_RISING_EDGE,
+};
+
+#define I8254_SYNAPSES_BASE(_id) ((_id) * I8254_SYNAPSES_PER_COUNT)
+#define I8254_SYNAPSE_CLK(_id) {					\
+	.actions_list	= i8254_clk_actions,				\
+	.num_actions	= ARRAY_SIZE(i8254_clk_actions),		\
+	.signal		= &i8254_signals[I8254_SYNAPSES_BASE(_id) + 0],	\
+}
+#define I8254_SYNAPSE_GATE(_id) {					\
+	.actions_list	= i8254_gate_actions,				\
+	.num_actions	= ARRAY_SIZE(i8254_gate_actions),		\
+	.signal		= &i8254_signals[I8254_SYNAPSES_BASE(_id) + 1],	\
+}
+
+static struct counter_synapse i8254_synapses[] = {
+	I8254_SYNAPSE_CLK(0), I8254_SYNAPSE_GATE(0),
+	I8254_SYNAPSE_CLK(1), I8254_SYNAPSE_GATE(1),
+	I8254_SYNAPSE_CLK(2), I8254_SYNAPSE_GATE(2),
+};
+
+static const enum counter_function i8254_functions_list[] = {
+	COUNTER_FUNCTION_DECREASE,
+};
+
+static const enum counter_count_mode i8254_count_modes[] = {
+	COUNTER_COUNT_MODE_INTERRUPT_ON_TERMINAL_COUNT,
+	COUNTER_COUNT_MODE_HARDWARE_RETRIGGERABLE_ONESHOT,
+	COUNTER_COUNT_MODE_RATE_GENERATOR,
+	COUNTER_COUNT_MODE_SQUARE_WAVE_MODE,
+	COUNTER_COUNT_MODE_SOFTWARE_TRIGGERED_STROBE,
+	COUNTER_COUNT_MODE_HARDWARE_TRIGGERED_STROBE,
+};
+
+static DEFINE_COUNTER_AVAILABLE(i8254_count_modes_available, i8254_count_modes);
+
+static struct counter_comp i8254_count_ext[] = {
+	COUNTER_COMP_CEILING(i8254_count_ceiling_read, NULL),
+	COUNTER_COMP_COUNT_MODE(i8254_count_mode_read, i8254_count_mode_write,
+				i8254_count_modes_available),
+	COUNTER_COMP_FLOOR(i8254_count_floor_read, NULL),
+	COUNTER_COMP_PRESET(i8254_count_preset_read, i8254_count_preset_write),
+};
+
+#define I8254_COUNT(_id, _name) {				\
+	.id = (_id),						\
+	.name = (_name),					\
+	.functions_list = i8254_functions_list,			\
+	.num_functions = ARRAY_SIZE(i8254_functions_list),	\
+	.synapses = &i8254_synapses[I8254_SYNAPSES_BASE(_id)],	\
+	.num_synapses =	I8254_SYNAPSES_PER_COUNT,		\
+	.ext = i8254_count_ext,					\
+	.num_ext = ARRAY_SIZE(i8254_count_ext)			\
+}
+
+static struct counter_count i8254_counts[I8254_NUM_COUNTERS] = {
+	I8254_COUNT(0, "Counter 0"), I8254_COUNT(1, "Counter 1"), I8254_COUNT(2, "Counter 2"),
+};
+
+/**
+ * devm_i8254_regmap_register - Register an i8254 Counter device
+ * @dev: device that is registering this i8254 Counter device
+ * @config: configuration for i8254_regmap_config
+ *
+ * Registers an Intel 8254 Programmable Interval Timer Counter device. Returns 0 on success and
+ * negative error number on failure.
+ */
+int devm_i8254_regmap_register(struct device *const dev,
+			       const struct i8254_regmap_config *const config)
+{
+	struct counter_device *counter;
+	struct i8254 *priv;
+	int err;
+
+	if (!config->parent)
+		return -EINVAL;
+
+	if (!config->map)
+		return -EINVAL;
+
+	counter = devm_counter_alloc(dev, sizeof(*priv));
+	if (!counter)
+		return -ENOMEM;
+	priv = counter_priv(counter);
+	priv->map = config->map;
+
+	counter->name = dev_name(config->parent);
+	counter->parent = config->parent;
+	counter->ops = &i8254_ops;
+	counter->counts = i8254_counts;
+	counter->num_counts = ARRAY_SIZE(i8254_counts);
+	counter->signals = i8254_signals;
+	counter->num_signals = ARRAY_SIZE(i8254_signals);
+
+	mutex_init(&priv->lock);
+
+	err = i8254_init_hw(priv->map);
+	if (err)
+		return err;
+
+	err = devm_counter_add(dev, counter);
+	if (err < 0)
+		return dev_err_probe(dev, err, "Failed to add counter\n");
+
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(devm_i8254_regmap_register, I8254);
+
+MODULE_AUTHOR("William Breathitt Gray");
+MODULE_DESCRIPTION("Intel 8254 Programmable Interval Timer");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS(COUNTER);