Message-Id: <1299385050-13674-2-git-send-email-bgat@billgatliff.com>
Date:	Sat,  5 Mar 2011 22:17:28 -0600
From:	Bill Gatliff <bgat@...lgatliff.com>
To:	linux-kernel@...r.kernel.org
Cc:	Bill Gatliff <bgat@...lgatliff.com>
Subject: [PWM v6 1/3] PWM: Implement a generic PWM framework

Updates the existing PWM-related functions to support multiple
and/or hotplugged PWM devices, and adds a sysfs interface.
Moves the code to drivers/pwm.

For now, this new code can exist alongside the current PWM
implementations; the existing implementations will be migrated
to this new framework as time permits.  Eventually, the current
PWM implementation will be deprecated and then expunged.

Signed-off-by: Bill Gatliff <bgat@...lgatliff.com>
---
 Documentation/pwm.txt   |  277 +++++++++++++++++++++
 drivers/Kconfig         |    2 +
 drivers/Makefile        |    2 +
 drivers/pwm/Kconfig     |   10 +
 drivers/pwm/Makefile    |    4 +
 drivers/pwm/pwm.c       |  610 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pwm/pwm.h |  155 ++++++++++++
 7 files changed, 1060 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/pwm.txt
 create mode 100644 drivers/pwm/Kconfig
 create mode 100644 drivers/pwm/Makefile
 create mode 100644 drivers/pwm/pwm.c
 create mode 100644 include/linux/pwm/pwm.h

diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
new file mode 100644
index 0000000..2b15395
--- /dev/null
+++ b/Documentation/pwm.txt
@@ -0,0 +1,277 @@
+                       Generic PWM Device API
+
+                          February 7, 2011
+                            Bill Gatliff
+                        <bgat@...lgatliff.com>
+
+
+
+The code in drivers/pwm and include/linux/pwm/ implements an API for
+applications involving pulse-width-modulation signals.  This document
+describes how the API implementation facilitates both PWM-generating
+devices, and users of those devices.
+
+
+
+Motivation
+
+The primary goals for implementing the "generic PWM API" are to
+consolidate the various PWM implementations within a consistent and
+redundancy-reducing framework, and to facilitate the use of
+hotpluggable PWM devices.
+
+Previous PWM-related implementations within the Linux kernel achieved
+their consistency via cut-and-paste, but did not need to (and didn't)
+facilitate more than one PWM-generating device within the system---
+hotplug or otherwise.  The Generic PWM Device API might be most
+appropriately viewed as an update to those implementations, rather
+than a complete rewrite.
+
+
+
+Challenges
+
+One of the difficulties in implementing a generic PWM framework is the
+fact that pulse-width-modulation applications involve real-world
+signals, which often must be carefully managed to prevent destruction
+of hardware that is linked to those signals.  A DC motor that
+experiences a brief interruption in the PWM signal controlling it
+might destructively overheat; it could suddenly change speed, losing
+synchronization with a sensor; it could even suddenly change direction
+or torque, breaking the mechanical device connected to it.
+
+(A generic PWM device framework is not directly responsible for
+preventing the above scenarios: that responsibility lies with the
+hardware designer, and the application and driver authors.  But it
+must to the greatest extent possible make it easy to avoid such
+problems).
+
+A generic PWM device framework must accommodate the substantial
+differences between available PWM-generating hardware devices, without
+becoming sub-optimal for any of them.
+
+Finally, a generic PWM device framework must be relatively
+lightweight, computationally speaking.  Some PWM users demand
+high-speed outputs, plus the ability to regulate those outputs
+quickly.  A device framework must be able to "keep up" with such
+hardware, while still leaving time to do real work.
+
+The Generic PWM Device API is an attempt to meet all of the above
+requirements.  At its initial publication, the API was already in use
+managing small DC motors, sensors and solenoids through a
+custom-designed, optically-isolated H-bridge driver.
+
+
+
+Functional Overview
+
+The Generic PWM Device API framework is implemented in
+include/linux/pwm/pwm.h and drivers/pwm/pwm.c.  The functions therein
+use information from pwm_device and pwm__config structures to invoke
+services in PWM peripheral device drivers.  Consult
+drivers/pwm/atmel-pwmc.c for an example driver for the Atmel PWMC
+peripheral.
+
+There are two classes of adopters of the PWM framework:
+
+  Users -- those wishing to employ the API merely to produce PWM
+  signals; once they have identified the appropriate physical output
+  on the platform in question, they don't care about the details of
+  the underlying hardware
+
+  Driver authors -- those wishing to bind devices that can generate
+  PWM signals to the Generic PWM Device API, so that the services of
+  those devices become available to users. Assuming the hardware can
+  support the needs of a user, driver authors don't care about the
+  details of the user's application
+
+Generally speaking, users will first invoke pwm_request() to obtain a
+handle to a PWM device.  They will then pass that handle to functions
+like pwm_duty_ns() and pwm_period_ns() to set the duty cycle and
+period of the PWM signal, respectively.  They will also invoke
+pwm_start() and pwm_stop() to turn the signal on and off.
+
+The Generic PWM API framework also provides a sysfs interface to PWM
+devices, which is adequate for basic application needs and testing.
+
+Driver authors fill out a pwm_device structure, which describes the
+capabilities of the PWM hardware being utilized.  They then invoke
+pwm_register() (usually from within their device's probe() handler) to
+make the PWM API aware of their device.  The framework will call back
+to the methods described in the pwm_device structure as users begin to
+configure and utilize the hardware.
+
+Many PWM-capable peripherals provide two, three, or more channels of
+PWM output.  The driver author completes and registers a pwm_device
+structure for each channel they wish to be supported by the Generic
+PWM API.
+
+Note that PWM signals can be produced by a variety of peripherals,
+beyond the true PWM peripherals offered by many system-on-chip
+devices.  Other possibilities include timer/counters with
+compare-match capabilities, carefully-programmed synchronous serial
+ports (e.g. SPI), and GPIO pins driven by kernel interval timers.
+With a proper pwm_device structure, these devices and pseudo-devices
+can be accommodated by the Generic PWM Device API framework.
+
+
+
+Using the API to Generate PWM Signals -- Basic Functions for Users
+
+
+pwm_request() -- Returns a pwm_device pointer, which is subsequently
+passed to the other user-related PWM functions.  Once requested, a PWM
+channel is marked as in-use and subsequent requests prior to
+pwm_release() will fail.
+
+The names used to refer to PWM devices are defined by driver authors.
+Typically they are platform device bus identifiers, and this
+convention is encouraged for consistency.
+
+
+pwm_release() -- Marks a PWM channel as no longer in use.  The PWM
+device is stopped before it is released by the API.
+
+
+pwm_period_ns() -- Specifies the PWM signal's period, in nanoseconds.
+
+
+pwm_duty_ns() -- Specifies the PWM signal's active duration, in nanoseconds.
+
+
+pwm_duty_percent() -- Specifies the PWM signal's active duration, as a
+percentage of the current period of the signal.  NOTE: this value is
+not recalculated if the period of the signal is subsequently changed.
+
+
+pwm_start(), pwm_stop() -- Turns the PWM signal on and off.  Except
+where stated otherwise by a driver author, signals are stopped at the
+end of the current period, at which time the output is set to its
+inactive state.
+
+
+pwm_polarity() -- Defines whether the PWM signal output's active
+region is "1" or "0".  A 10% duty-cycle, polarity=1 signal will
+conventionally be at 5V (or 3.3V, or 1000V, or whatever the platform
+hardware does) for 10% of the period.  The same configuration of a
+polarity=0 signal will be at 5V (or 3.3V, or ...) for 90% of the
+period.
+
+
+
+Using the API to Generate PWM Signals -- Advanced Functions
+
+
+pwm_config() -- Passes a pwm_config structure to the associated device
+driver.  This function is invoked by pwm_start(), pwm_duty_ns(),
+etc. and is one of two main entry points to the PWM driver for the
+hardware being used.  The configuration change is guaranteed atomic if
+multiple configuration changes are specified by the config structure.
+This function might sleep, depending on what the device driver has to
+do to satisfy the request.  All PWM device drivers must support this
+entry point.
+
+
+pwm_config_nosleep() -- Passes a pwm_config structure to the
+associated device driver.  If the driver must sleep in order to
+implement the requested configuration change, -EWOULDBLOCK is
+returned.  Users may call this function from interrupt handlers, timer
+handlers, and other interrupt contexts, but must confine their
+configuration changes to only those that the driver can implement
+without sleeping.  This is the other main entry point into the PWM
+hardware driver, but not all device drivers support this entry point.
+
+
+pwm_synchronize(), pwm_unsynchronize() -- "Synchronizes" two or more
+PWM channels, if the underlying hardware permits.  (If it doesn't, the
+framework facilitates emulating this capability but it is not yet
+implemented).  Synchronized channels will start and stop
+simultaneously when any single channel in the group is started or
+stopped.  Use pwm_unsynchronize(..., NULL) to completely detach a
+channel from any other synchronized channels.  By default, all PWM
+channels are unsynchronized.
+
+
+pwm_set_handler() -- Defines an end-of-period callback.  The indicated
+function will be invoked in a worker thread at the end of each PWM
+period, and can subsequently invoke pwm_config(), etc.  Must be used
+with extreme care for high-speed PWM outputs.  Set the handler
+function to NULL to un-set the handler.
+
+
+
+Implementing a PWM Device API Driver -- Functions for Driver Authors
+
+
+Fill out the appropriate fields in a pwm_device structure, and submit
+to pwm_register():
+
+
+bus_id -- the plain-text name of the device.  Users will bind to a
+channel on the device using this name plus the channel number.  For
+example, the Atmel PWMC's bus_id is "atmel_pwmc", the same as used by
+the platform device driver (recommended).  The first Atmel PWMC
+platform device registered thereby receives bus_id "atmel_pwmc.0",
+which is what you put in pwm_device.bus_id.  Channels are then named
+"atmel_pwmc.0:[0-3]".  (Hint: just use dev_name(pdev->dev) in your
+probe() method).
+
+
+request -- (optional) Invoked each time a user requests a channel.
+Use to turn on clocks, clean up register states, etc.  The framework
+takes care of device locking/unlocking; you will see only successful
+requests.
+
+
+free -- (optional) Invoked each time a user relinquishes a channel.
+The framework will have already stopped, unsynchronized and un-handled
+the channel.  Use to turn off clocks, etc. as necessary.
+
+
+set_callback -- (optional) If the hardware supports an end-of-period
+interrupt, invoke the function provided in this callback during the
+device's interrupt handler.  The callback function itself is always
+internal to the API, and does not map directly to the user's callback
+function.
+
+
+config -- Invoked to change the device configuration, always from a
+sleep-compatible context.  All the changes indicated must be performed
+atomically, ideally synchronized to an end-of-period event (so that
+you avoid short or long output pulses).  You may sleep, etc. as
+necessary within this function.
+
+
+config_nosleep -- (optional) Invoked to change device configuration
+from within a context that is not allowed to sleep.  If you cannot
+perform the requested configuration changes without sleeping, return
+-EWOULDBLOCK.
+
+
+
+FAQs and Additional Notes
+
+The Atmel PWMC pwm_config() function tries to satisfy the user's
+configuration request by first invoking pwm_config_nosleep().  If that
+operation fails, then the PWM peripheral is brought to a synchronized
+stop, the configuration changes are made, and the device is restarted.
+
+The Atmel PWMC's use of pwm_config_nosleep() from pwm_config()
+minimizes redundant code between the two functions, and relieves the
+pwm_config() function of the need to explicitly test whether a
+requested configuration change can be carried out while the PWM device
+is in its current mode.
+
+PWM API driver authors are encouraged to adopt the Atmel PWMC's
+pwm_config()-vs.-pwm_config_nosleep() strategy in implementations for
+other devices as well.
+
+
+
+Acknowledgements
+
+
+The author expresses his gratitude to the countless developers who
+have reviewed and submitted feedback on the various versions of the
+Generic PWM Device API code, and those who have submitted drivers and
+applications that use the framework.  You know who you are.  ;)
diff --git a/drivers/Kconfig b/drivers/Kconfig
index 9bfb71f..413e4f9 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -56,6 +56,8 @@ source "drivers/pps/Kconfig"
 
 source "drivers/gpio/Kconfig"
 
+source "drivers/pwm/Kconfig"
+
 source "drivers/w1/Kconfig"
 
 source "drivers/power/Kconfig"
diff --git a/drivers/Makefile b/drivers/Makefile
index b423bb1..4e37abf 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -6,6 +6,8 @@
 #
 
 obj-y				+= gpio/
+obj-$(CONFIG_GENERIC_PWM)	+= pwm/
+
 obj-$(CONFIG_PCI)		+= pci/
 obj-$(CONFIG_PARISC)		+= parisc/
 obj-$(CONFIG_RAPIDIO)		+= rapidio/
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
new file mode 100644
index 0000000..bc550f7
--- /dev/null
+++ b/drivers/pwm/Kconfig
@@ -0,0 +1,10 @@
+#
+# PWM infrastructure and devices
+#
+
+menuconfig GENERIC_PWM
+	tristate "PWM Support"
+	help
+	  Enables PWM device support implemented via a generic
+	  framework.  If unsure, say N.
+
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
new file mode 100644
index 0000000..7baa201
--- /dev/null
+++ b/drivers/pwm/Makefile
@@ -0,0 +1,4 @@
+#
+# Makefile for pwm devices
+#
+obj-$(CONFIG_GENERIC_PWM) := pwm.o
diff --git a/drivers/pwm/pwm.c b/drivers/pwm/pwm.c
new file mode 100644
index 0000000..f958e4b
--- /dev/null
+++ b/drivers/pwm/pwm.c
@@ -0,0 +1,610 @@
+/*
+ * PWM API implementation
+ *
+ * Copyright (C) 2011 Bill Gatliff <bgat@...lgatliff.com>
+ * Copyright (C) 2011 Arun Murthy <arun.murthy@...ricsson.com>
+ *
+ * This program is free software; you may redistribute and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ * USA
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <linux/completion.h>
+#include <linux/workqueue.h>
+#include <linux/list.h>
+#include <linux/sched.h>
+#include <linux/pwm/pwm.h>
+
+static const char *REQUEST_SYSFS = "sysfs";
+static LIST_HEAD(pwm_device_list);
+static DEFINE_MUTEX(device_list_mutex);
+static struct class pwm_class;
+static struct workqueue_struct *pwm_handler_workqueue;
+
+static int pwm_match_name(struct device *dev, void *name)
+{
+	return !strcmp(name, dev_name(dev));
+}
+
+static int __pwm_request(struct pwm_device *p, const char *label)
+{
+	int ret;
+
+	ret = test_and_set_bit(FLAG_REQUESTED, &p->flags);
+	if (ret) {
+		ret = -EBUSY;
+		goto done;
+	}
+
+	p->label = label;
+
+	if (p->ops->request) {
+		ret = p->ops->request(p);
+		if (ret) {
+			clear_bit(FLAG_REQUESTED, &p->flags);
+			goto done;
+		}
+	}
+
+done:
+	return ret;
+}
+
+static struct pwm_device *__pwm_request_byname(const char *name,
+					       const char *label)
+{
+	struct device *d;
+	struct pwm_device *p;
+	int ret;
+
+	d = class_find_device(&pwm_class, NULL, (char*)name, pwm_match_name);
+	if (IS_ERR_OR_NULL(d))
+		return ERR_PTR(-EINVAL);
+
+	p = dev_get_drvdata(d);
+	ret = __pwm_request(p, label);
+
+	if (ret)
+		return ERR_PTR(ret);
+	return p;
+}
+
+struct pwm_device *pwm_request_byname(const char *name, const char *label)
+{
+	struct pwm_device *p;
+
+	mutex_lock(&device_list_mutex);
+	p = __pwm_request_byname(name, label);
+	mutex_unlock(&device_list_mutex);
+	return p;
+}
+EXPORT_SYMBOL(pwm_request_byname);
+
+struct pwm_device *pwm_request(const char *bus_id, int id, const char *label)
+{
+	char name[256];
+	int ret;
+
+	if (id == -1)
+		ret = scnprintf(name, sizeof name, "%s", bus_id);
+	else
+		ret = scnprintf(name, sizeof name, "%s:%d", bus_id, id);
+	if (ret <= 0 || ret >= sizeof name)
+		return ERR_PTR(-EINVAL);
+
+	return pwm_request_byname(name, label);
+}
+EXPORT_SYMBOL(pwm_request);
+
+void pwm_release(struct pwm_device *p)
+{
+	mutex_lock(&device_list_mutex);
+
+	if (!test_and_clear_bit(FLAG_REQUESTED, &p->flags)) {
+		WARN(1, "%s: releasing unrequested PWM device %s\n",
+		     __func__, dev_name(p->dev));
+		goto done;
+	}
+
+	pwm_stop(p);
+	pwm_unsynchronize(p, NULL);
+	pwm_set_handler(p, NULL, NULL);
+
+	p->label = NULL;
+
+	if (p->ops->release)
+		p->ops->release(p);
+done:
+	mutex_unlock(&device_list_mutex);
+}
+EXPORT_SYMBOL(pwm_release);
+
+static unsigned long pwm_ns_to_ticks(struct pwm_device *p, unsigned long nsecs)
+{
+	unsigned long long ticks;
+
+	ticks = nsecs;
+	ticks *= p->tick_hz;
+	do_div(ticks, 1000000000);
+	return ticks;
+}
+
+static unsigned long pwm_ticks_to_ns(struct pwm_device *p, unsigned long ticks)
+{
+	unsigned long long ns;
+
+	if (!p->tick_hz)
+		return 0;
+
+	ns = ticks;
+	ns *= 1000000000UL;
+	do_div(ns, p->tick_hz);
+	return ns;
+}
+
+int pwm_config_nosleep(struct pwm_device *p, struct pwm_config *c)
+{
+	if (!p->ops->config_nosleep)
+		return -EINVAL;
+
+	return p->ops->config_nosleep(p, c);
+}
+EXPORT_SYMBOL(pwm_config_nosleep);
+
+int pwm_config(struct pwm_device *p, struct pwm_config *c)
+{
+	int ret = 0;
+
+	switch (c->config_mask & (BIT(PWM_CONFIG_PERIOD_TICKS)
+				  | BIT(PWM_CONFIG_DUTY_TICKS))) {
+	case BIT(PWM_CONFIG_PERIOD_TICKS):
+		if (p->duty_ticks > c->period_ticks) {
+			ret = -EINVAL;
+			goto err;
+		}
+		break;
+	case BIT(PWM_CONFIG_DUTY_TICKS):
+		if (p->period_ticks < c->duty_ticks) {
+			ret = -EINVAL;
+			goto err;
+		}
+		break;
+	case BIT(PWM_CONFIG_DUTY_TICKS) | BIT(PWM_CONFIG_PERIOD_TICKS):
+		if (c->duty_ticks > c->period_ticks) {
+			ret = -EINVAL;
+			goto err;
+		}
+		break;
+	default:
+		break;
+	}
+
+err:
+	dev_dbg(p->dev, "%s: config_mask %lu period_ticks %lu "
+		"duty_ticks %lu polarity %d\n",
+		__func__, c->config_mask, c->period_ticks,
+		c->duty_ticks, c->polarity);
+
+	if (ret)
+		return ret;
+	return p->ops->config(p, c);
+}
+EXPORT_SYMBOL(pwm_config);
+
+int pwm_set(struct pwm_device *p, unsigned long period_ns,
+	    unsigned long duty_ns, int active_high)
+{
+	struct pwm_config c = {
+		.config_mask = (BIT(PWM_CONFIG_PERIOD_TICKS)
+				| BIT(PWM_CONFIG_DUTY_TICKS)
+				| BIT(PWM_CONFIG_POLARITY)),
+		.period_ticks = pwm_ns_to_ticks(p, period_ns),
+		.duty_ticks = pwm_ns_to_ticks(p, duty_ns),
+		.polarity = active_high
+	};
+
+	return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_set);
+
+int pwm_set_period_ns(struct pwm_device *p, unsigned long period_ns)
+{
+	struct pwm_config c = {
+		.config_mask = BIT(PWM_CONFIG_PERIOD_TICKS),
+		.period_ticks = pwm_ns_to_ticks(p, period_ns),
+	};
+
+	return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_set_period_ns);
+
+unsigned long pwm_get_period_ns(struct pwm_device *p)
+{
+	return pwm_ticks_to_ns(p, p->period_ticks);
+}
+EXPORT_SYMBOL(pwm_get_period_ns);
+
+int pwm_set_duty_ns(struct pwm_device *p, unsigned long duty_ns)
+{
+	struct pwm_config c = {
+		.config_mask = BIT(PWM_CONFIG_DUTY_TICKS),
+		.duty_ticks = pwm_ns_to_ticks(p, duty_ns),
+	};
+	return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_set_duty_ns);
+
+unsigned long pwm_get_duty_ns(struct pwm_device *p)
+{
+	return pwm_ticks_to_ns(p, p->duty_ticks);
+}
+EXPORT_SYMBOL(pwm_get_duty_ns);
+
+int pwm_set_polarity(struct pwm_device *p, int active_high)
+{
+	struct pwm_config c = {
+		.config_mask = BIT(PWM_CONFIG_POLARITY),
+		.polarity = active_high,
+	};
+	return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_set_polarity);
+
+int pwm_start(struct pwm_device *p)
+{
+	struct pwm_config c = {
+		.config_mask = BIT(PWM_CONFIG_START),
+	};
+	return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_start);
+
+int pwm_stop(struct pwm_device *p)
+{
+	struct pwm_config c = {
+		.config_mask = BIT(PWM_CONFIG_STOP),
+	};
+	return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_stop);
+
+int pwm_synchronize(struct pwm_device *p, struct pwm_device *to_p)
+{
+	if (!p->ops->synchronize)
+		return -EINVAL;
+
+	return p->ops->synchronize(p, to_p);
+}
+EXPORT_SYMBOL(pwm_synchronize);
+
+int pwm_unsynchronize(struct pwm_device *p, struct pwm_device *from_p)
+{
+	if (!p->ops->unsynchronize)
+		return -EINVAL;
+
+	return p->ops->unsynchronize(p, from_p);
+}
+EXPORT_SYMBOL(pwm_unsynchronize);
+
+static void pwm_handler(struct work_struct *w)
+{
+	struct pwm_device *p = container_of(w, struct pwm_device,
+					    handler_work);
+	if (p->handler)
+		p->handler(p, p->handler_data);
+}
+
+void pwm_callback(struct pwm_device *p)
+{
+	queue_work(pwm_handler_workqueue, &p->handler_work);
+}
+EXPORT_SYMBOL(pwm_callback);
+
+int pwm_set_handler(struct pwm_device *p, pwm_handler_t handler, void *data)
+{
+	struct pwm_config c;
+	int ret;
+
+	if (handler)
+		c.config_mask = BIT(PWM_CONFIG_ENABLE_CALLBACK);
+	else
+		c.config_mask = BIT(PWM_CONFIG_DISABLE_CALLBACK);
+
+	ret = pwm_config(p, &c);
+
+	if (!ret && handler) {
+		p->handler_data = data;
+		p->handler = handler;
+		INIT_WORK(&p->handler_work, pwm_handler);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(pwm_set_handler);
+
+static ssize_t pwm_run_show(struct device *dev,
+			    struct device_attribute *attr,
+			    char *buf)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+	return sprintf(buf, "%d\n", pwm_is_running(p));
+}
+
+static ssize_t pwm_run_store(struct device *dev,
+			     struct device_attribute *attr,
+			     const char *buf, size_t len)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+
+	if (!pwm_is_exported(p))
+		return -EINVAL;
+
+	if (sysfs_streq(buf, "1"))
+		pwm_start(p);
+	else if (sysfs_streq(buf, "0"))
+		pwm_stop(p);
+
+	return len;
+}
+static DEVICE_ATTR(run, S_IRUGO | S_IWUSR, pwm_run_show, pwm_run_store);
+
+static ssize_t pwm_tick_hz_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+	return sprintf(buf, "%lu\n", p->tick_hz);
+}
+static DEVICE_ATTR(tick_hz, S_IRUGO, pwm_tick_hz_show, NULL);
+
+static ssize_t pwm_duty_ns_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+	return sprintf(buf, "%lu\n", pwm_get_duty_ns(p));
+}
+
+static ssize_t pwm_duty_ns_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf, size_t len)
+{
+	unsigned long duty_ns;
+	struct pwm_device *p = dev_get_drvdata(dev);
+
+	if (!pwm_is_exported(p))
+		return -EINVAL;
+
+	if (!strict_strtoul(buf, 10, &duty_ns))
+		pwm_set_duty_ns(p, duty_ns);
+	return len;
+}
+static DEVICE_ATTR(duty_ns, S_IRUGO | S_IWUSR, pwm_duty_ns_show, pwm_duty_ns_store);
+
+static ssize_t pwm_period_ns_show(struct device *dev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+	return sprintf(buf, "%lu\n", pwm_get_period_ns(p));
+}
+
+static ssize_t pwm_period_ns_store(struct device *dev,
+				   struct device_attribute *attr,
+				   const char *buf, size_t len)
+{
+	unsigned long period_ns;
+	struct pwm_device *p = dev_get_drvdata(dev);
+
+	if (!pwm_is_exported(p))
+		return -EINVAL;
+
+	if (!strict_strtoul(buf, 10, &period_ns))
+		pwm_set_period_ns(p, period_ns);
+	return len;
+}
+static DEVICE_ATTR(period_ns, S_IRUGO | S_IWUSR, pwm_period_ns_show, pwm_period_ns_store);
+
+static ssize_t pwm_polarity_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+	return sprintf(buf, "%d\n", p->active_high ? 1 : 0);
+}
+
+static ssize_t pwm_polarity_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	unsigned long polarity;
+	struct pwm_device *p = dev_get_drvdata(dev);
+
+	if (!pwm_is_exported(p))
+		return -EINVAL;
+
+	if (!strict_strtoul(buf, 10, &polarity))
+		pwm_set_polarity(p, polarity);
+	return len;
+}
+static DEVICE_ATTR(polarity, S_IRUGO | S_IWUSR, pwm_polarity_show, pwm_polarity_store);
+
+static ssize_t pwm_request_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+	int ret;
+
+	mutex_lock(&device_list_mutex);
+	ret = __pwm_request(p, REQUEST_SYSFS);
+	mutex_unlock(&device_list_mutex);
+
+	if (!ret)
+		set_bit(FLAG_EXPORTED, &p->flags);
+
+	return sprintf(buf, "%s\n", p->label);
+}
+
+static ssize_t pwm_request_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf, size_t len)
+{
+	struct pwm_device *p = dev_get_drvdata(dev);
+
+	pwm_release(p);
+	clear_bit(FLAG_EXPORTED, &p->flags);
+	return len;
+}
+static DEVICE_ATTR(request, S_IRUGO | S_IWUSR, pwm_request_show, pwm_request_store);
+
+static const struct attribute *pwm_attrs[] = {
+	&dev_attr_tick_hz.attr,
+	&dev_attr_run.attr,
+	&dev_attr_polarity.attr,
+	&dev_attr_duty_ns.attr,
+	&dev_attr_period_ns.attr,
+	&dev_attr_request.attr,
+	NULL,
+};
+
+static const struct attribute_group pwm_device_attr_group = {
+	.attrs = (struct attribute **) pwm_attrs,
+};
+
+static struct class_attribute pwm_class_attrs[] = {
+	__ATTR_NULL,
+};
+
+static struct class pwm_class = {
+	.name = "pwm",
+	.owner = THIS_MODULE,
+
+	.class_attrs = pwm_class_attrs,
+};
+
+int pwm_register_byname(struct pwm_device *p, struct device *parent,
+			const char *name)
+{
+	struct device *d;
+	int ret;
+
+	if (!p->ops || !p->ops->config)
+		return -EINVAL;
+
+	mutex_lock(&device_list_mutex);
+
+	d = class_find_device(&pwm_class, NULL, (char*)name, pwm_match_name);
+	if (d) {
+		ret = -EEXIST;
+		goto err_found_device;
+	}
+
+	p->dev = device_create(&pwm_class, parent, MKDEV(0, 0), NULL, name);
+	if (IS_ERR(p->dev)) {
+		ret = PTR_ERR(p->dev);
+		goto err_device_create;
+	}
+
+	ret = sysfs_create_group(&p->dev->kobj, &pwm_device_attr_group);
+	if (ret)
+		goto err_create_group;
+
+	dev_set_drvdata(p->dev, p);
+	p->flags = BIT(FLAG_REGISTERED);
+
+	goto done;
+
+err_create_group:
+	device_unregister(p->dev);
+	p->flags = 0;
+
+err_device_create:
+err_found_device:
+done:
+	mutex_unlock(&device_list_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL(pwm_register_byname);
+
+int pwm_register(struct pwm_device *p, struct device *parent, int id)
+{
+	int ret;
+	char name[256];
+
+	if (IS_ERR_OR_NULL(parent))
+		return -EINVAL;
+
+	if (id == -1)
+		ret = scnprintf(name, sizeof name, "%s", dev_name(parent));
+	else
+		ret = scnprintf(name, sizeof name, "%s:%d", dev_name(parent), id);
+	if (ret <= 0 || ret >= sizeof name)
+		return -EINVAL;
+
+	return pwm_register_byname(p, parent, name);
+}
+EXPORT_SYMBOL(pwm_register);
+
+int pwm_unregister(struct pwm_device *p)
+{
+	int ret = 0;
+
+	mutex_lock(&device_list_mutex);
+
+	if (pwm_is_running(p) || pwm_is_requested(p)) {
+		ret = -EBUSY;
+		goto done;
+	}
+
+	sysfs_remove_group(&p->dev->kobj, &pwm_device_attr_group);
+	device_unregister(p->dev);
+	p->flags = 0;
+
+done:
+	mutex_unlock(&device_list_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL(pwm_unregister);
+
+static int __init pwm_init(void)
+{
+	pwm_handler_workqueue = create_singlethread_workqueue("pwm");
+	if (IS_ERR_OR_NULL(pwm_handler_workqueue)) {
+		pr_err("%s: failed to create PWM workqueue; aborting\n",
+		       __func__);
+		return -ENOMEM;
+	}
+
+	return class_register(&pwm_class);
+}
+
+static void __exit pwm_exit(void)
+{
+	destroy_workqueue(pwm_handler_workqueue);
+	class_unregister(&pwm_class);
+}
+
+postcore_initcall(pwm_init);
+module_exit(pwm_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Bill Gatliff <bgat@...lgatliff.com>");
+MODULE_DESCRIPTION("Generic PWM device API implementation");
diff --git a/include/linux/pwm/pwm.h b/include/linux/pwm/pwm.h
new file mode 100644
index 0000000..1447333
--- /dev/null
+++ b/include/linux/pwm/pwm.h
@@ -0,0 +1,155 @@
+/*
+ * Copyright (C) 2011 Bill Gatliff < bgat@...lgatliff.com>
+ * Copyright (C) 2011 Arun Murthy <arun.murth@...ricsson.com>
+ *
+ * This program is free software; you may redistribute and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ * USA
+ */
+#ifndef __LINUX_PWM_H
+#define __LINUX_PWM_H
+
+enum {
+	FLAG_REGISTERED		= 0,
+	FLAG_REQUESTED		= 1,
+	FLAG_STOP		= 2,
+	FLAG_RUNNING		= 3,
+	FLAG_EXPORTED		= 4,
+};
+
+enum {
+	PWM_CONFIG_DUTY_TICKS	= 0,
+	PWM_CONFIG_PERIOD_TICKS	= 1,
+	PWM_CONFIG_POLARITY	= 2,
+	PWM_CONFIG_START	= 3,
+	PWM_CONFIG_STOP		= 4,
+
+	PWM_CONFIG_ENABLE_CALLBACK = 9,
+	PWM_CONFIG_DISABLE_CALLBACK = 10,
+};
+
+struct pwm_config;
+struct pwm_device;
+
+typedef int (*pwm_handler_t)(struct pwm_device *p, void *data);
+typedef void (*pwm_callback_t)(struct pwm_device *p);
+
+struct pwm_device_ops {
+	int	(*request)		(struct pwm_device *p);
+	void	(*release)		(struct pwm_device *p);
+	int	(*config)		(struct pwm_device *p,
+					 struct pwm_config *c);
+	int	(*config_nosleep)	(struct pwm_device *p,
+					 struct pwm_config *c);
+	int	(*synchronize)		(struct pwm_device *p,
+					 struct pwm_device *to_p);
+	int	(*unsynchronize)	(struct pwm_device *p,
+					 struct pwm_device *from_p);
+};
+
+struct pwm_config {
+	unsigned long config_mask;
+
+	unsigned long duty_ticks;
+	unsigned long period_ticks;
+	int polarity;
+};
+
+struct pwm_device {
+	struct device *dev;
+	const struct pwm_device_ops *ops;
+
+	const void *data;
+
+	const char *label;
+
+	unsigned long flags;
+
+	unsigned long tick_hz;
+
+	struct work_struct handler_work;
+	pwm_handler_t handler;
+	void *handler_data;
+
+	int active_high;
+	unsigned long period_ticks;
+	unsigned long duty_ticks;
+};
+
+struct pwm_device *pwm_request_byname(const char *name, const char *label);
+struct pwm_device *pwm_request(const char *bus_id, int id, const char *label);
+void pwm_release(struct pwm_device *p);
+
+static inline int pwm_is_registered(const struct pwm_device *p)
+{
+	return test_bit(FLAG_REGISTERED, &p->flags);
+}
+
+static inline int pwm_is_requested(const struct pwm_device *p)
+{
+	return test_bit(FLAG_REQUESTED, &p->flags);
+}
+
+static inline int pwm_is_running(const struct pwm_device *p)
+{
+	return test_bit(FLAG_RUNNING, &p->flags);
+}
+
+static inline int pwm_is_exported(const struct pwm_device *p)
+{
+	return test_bit(FLAG_EXPORTED, &p->flags);
+}
+
+static inline void pwm_set_drvdata(struct pwm_device *p, const void *data)
+{
+	p->data = data;
+}
+
+static inline void *pwm_get_drvdata(const struct pwm_device *p)
+{
+	return (void*)p->data;
+}
+
+
+int pwm_register(struct pwm_device *p, struct device *parent, int id);
+int pwm_register_byname(struct pwm_device *p, struct device *parent,
+			const char *name);
+int pwm_unregister(struct pwm_device *p);
+
+int pwm_set(struct pwm_device *p, unsigned long period_ns,
+	    unsigned long duty_ns, int active_high);
+
+int pwm_set_period_ns(struct pwm_device *p, unsigned long period_ns);
+unsigned long pwm_get_period_ns(struct pwm_device *p);
+
+int pwm_set_duty_ns(struct pwm_device *p, unsigned long duty_ns);
+unsigned long pwm_get_duty_ns(struct pwm_device *p);
+
+int pwm_set_polarity(struct pwm_device *p, int active_high);
+
+int pwm_start(struct pwm_device *p);
+int pwm_stop(struct pwm_device *p);
+
+int pwm_config_nosleep(struct pwm_device *p, struct pwm_config *c);
+int pwm_config(struct pwm_device *p, struct pwm_config *c);
+
+int pwm_synchronize(struct pwm_device *p, struct pwm_device *to_p);
+int pwm_unsynchronize(struct pwm_device *p, struct pwm_device *from_p);
+int pwm_set_handler(struct pwm_device *p, pwm_handler_t handler, void *data);
+
+void pwm_callback(struct pwm_device *p);
+
+struct pwm_device *gpio_pwm_create(int gpio);
+int gpio_pwm_destroy(struct pwm_device *p);
+
+#endif
-- 
1.7.2.3

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