An API that consolidates PWM-capable devices behind a common interface.
This code defines a pwm_device structure, which identifies a PWM-capable
platform device having one or more output channels of type pwm_channel. The
pwm_register() function maintains a list of pwm_devices; the pwm_request()
and pwm_free() functions allocate and un-allocate PWM channels on user
request.
The pwm_config_nosleep() and pwm_config() functions are the main entry
points into the PWM device driver itself. The former may be called
from contexts that are not allowed to sleep, i.e. interrupt handlers, and
will return an error if the requested configuration change cannot be
performed by the hardware without sleeping; the latter may be called
everywhere else.
PWM drivers might sleep because some hardware makes it difficult to update
the period, duty cycle or polarity of an output while the peripheral is
running. The Atmel PWMC peripheral is one example: the duty cycle and
period control registers share a single buffer register, but some
updates require changes to both registers and/or registers that aren't
buffered. When that is required, you must stop the peripheral at
the end of a PWM period in order to make the state change. The Atmel PWMC
driver implements the stop by sleeping until the end of the period.
An alternative implementation is to simply brute-force stop the PWM,
update the peripheral control registers, and then restart the hardware.
That approach is fine if you don't care about glitches in the PWM output.
The Atmel PWMC driver tries to be more elegant, at the expense of some
complexity and occasional conflict with sleep-prohibited contexts.
If you don't need to sleep or you don't care about glitch-free
operation, then put everything into pwm_config_nosleep()
and redirect pwm_config() there.
There are various helper functions that build the pwm_channel_config
structure for simple updates, like just modifying the duty cycle
percentage. These should probably be inlined, but aren't.
PWM channels can be "synchronized". As defined by this API, synchronized
PWM channels all start, stop and restart together when any channel in the
group is started, stopped, or restarted. The Atmel PWMC driver emulates
this behavior; other hardware might support it more explicitly. There is
currently no implementation to synchronize channels across PWM devices,
but the API will allow for that if someone wants to write the code.
Hint: there will be a measurable delay between starting and stopping the
various channels in a cross-device synchronization scenario, because
you'll have to start and stop each channel individually.
Finally, the pwm_set_handler() function registers a callback function that
the API will invoke in a worker thread at the end of the PWM period.
Signed-off-by: Bill Gatliff <bgat@xxxxxxxxxxxxxxx>
---
drivers/pwm/pwm.c | 681 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 681 insertions(+), 0 deletions(-)
create mode 100644 drivers/pwm/pwm.c
diff --git a/drivers/pwm/pwm.c b/drivers/pwm/pwm.c
new file mode 100644
index 0000000..5009de9
--- /dev/null
+++ b/drivers/pwm/pwm.c
@@ -0,0 +1,681 @@
+/*
+ * drivers/pwm/pwm.c
+ *
+ * Copyright (C) 2008 Bill Gatliff
+ *
+ * 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.
+ *
+ * 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/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/spinlock.h>
+#include <linux/fs.h>
+#include <linux/completion.h>
+#include <linux/workqueue.h>
+#include <linux/pwm.h>
+
+
+static int __pwm_create_sysfs(struct pwm_device *pwm);
+
+static LIST_HEAD(pwm_device_list);
+static DEFINE_MUTEX(device_list_mutex);
+static struct class pwm_class;
+static struct workqueue_struct *pwm_handler_workqueue;
+
+
+int pwm_register(struct pwm_device *pwm)
+{
+ struct pwm_channel *p;
+ int wchan;
+ int ret = 0;
+
+ spin_lock_init(&pwm->list_lock);
+
+ p = kcalloc(pwm->nchan, sizeof(struct pwm_channel), GFP_KERNEL);
+ if (!p)
+ return -ENOMEM;
+
+ for (wchan = 0; wchan < pwm->nchan; wchan++) {
+ spin_lock_init(&p[wchan].lock);
+ init_completion(&p[wchan].complete);
+ p[wchan].chan = wchan;
+ p[wchan].pwm = pwm;
+ }
+
+ pwm->channels = p;
+
+ mutex_lock(&device_list_mutex);
+
+ list_add_tail(&pwm->list, &pwm_device_list);
+ ret = __pwm_create_sysfs(pwm);
+ if (ret) {
+ mutex_unlock(&device_list_mutex);
+ goto err_create_sysfs;
+ }
+
+ mutex_unlock(&device_list_mutex);
+
+ pr_info("%s: %d channels\n", pwm->bus_id, pwm->nchan);
+ return 0;
+
+err_create_sysfs:
+ kfree(p);
+
+ return ret;
+}
+EXPORT_SYMBOL(pwm_register);
+
+
+static int __match_device(struct device *dev, void *data)
+{
+ return dev_get_drvdata(dev) == data;
+}
+
+
+int pwm_unregister(struct pwm_device *pwm)
+{
+ int wchan;
+ struct device *dev;
+
+ mutex_lock(&device_list_mutex);
+
+ for (wchan = 0; wchan < pwm->nchan; wchan++) {
+ if (pwm->channels[wchan].flags & FLAG_REQUESTED) {
+ mutex_unlock(&device_list_mutex);
+ return -EBUSY;
+ }
+ }
+
+ for (wchan = 0; wchan < pwm->nchan; wchan++) {
+ dev = class_find_device(&pwm_class, NULL,
+ &pwm->channels[wchan],
+ __match_device);
+ if (dev) {
+ put_device(dev);
+ device_unregister(dev);
+ }
+ }
+
+ kfree(pwm->channels);
+ list_del(&pwm->list);
+ mutex_unlock(&device_list_mutex);
+
+ return 0;
+}
+EXPORT_SYMBOL(pwm_unregister);
+
+
+static struct pwm_device *
+__pwm_find_device(const char *bus_id)
+{
+ struct pwm_device *p;
+
+ list_for_each_entry(p, &pwm_device_list, list)
+ {
+ if (!strcmp(bus_id, p->bus_id))
+ return p;
+ }
+ return NULL;
+}
+
+
+static int
+__pwm_request_channel(struct pwm_channel *p,
+ const char *requester)
+{
+ int ret;
+
+ if (test_and_set_bit(FLAG_REQUESTED, &p->flags))
+ return -EBUSY;
+
+ if (p->pwm->request) {
+ ret = p->pwm->request(p);
+ if (ret) {
+ clear_bit(FLAG_REQUESTED, &p->flags);
+ return ret;
+ }
+ }
+
+ p->requester = requester;
+ return 0;
+}
+
+
+struct pwm_channel *
+pwm_request(const char *bus_id,
+ int chan,
+ const char *requester)
+{
+ struct pwm_device *p;
+ int ret;
+
+ mutex_lock(&device_list_mutex);
+
+ p = __pwm_find_device(bus_id);
+ if (!p || chan >= p->nchan)
+ goto err_no_device;
+
+ if (!try_module_get(p->owner))
+ goto err_module_get_failed;
+
+ ret = __pwm_request_channel(&p->channels[chan], requester);
+ if (ret)
+ goto err_request_failed;
+
+ mutex_unlock(&device_list_mutex);
+
+ pr_debug("%s: %s:%d returns %p\n", __func__,
+ bus_id, chan, &p->channels[chan]);
+
+ return &p->channels[chan];
+
+err_request_failed:
+ module_put(p->owner);
+err_module_get_failed:
+err_no_device:
+
+ mutex_unlock(&device_list_mutex);
+
+ pr_debug("%s: %s:%d returns NULL\n",
+ __func__, bus_id, chan);
+
+ return NULL;
+}
+EXPORT_SYMBOL(pwm_request);
+
+
+void pwm_free(struct pwm_channel *p)
+{
+ mutex_lock(&device_list_mutex);
+
+ if (!test_and_clear_bit(FLAG_REQUESTED, &p->flags))
+ goto done;
+
+ pwm_stop(p);
+ pwm_unsynchronize(p, NULL);
+ pwm_set_handler(p, NULL, NULL);
+
+ if (p->pwm->free)
+ p->pwm->free(p);
+ module_put(p->pwm->owner);
+
+ pr_debug("%s: %s:%d free\n",
+ __func__, p->pwm->bus_id, p->chan);
+
+done:
+ mutex_unlock(&device_list_mutex);
+}
+EXPORT_SYMBOL(pwm_free);
+
+
+unsigned long pwm_ns_to_ticks(struct pwm_channel *p,
+ unsigned long nsecs)
+{
+ unsigned long long ticks;
+
+ ticks = nsecs;
+ ticks *= p->tick_hz;
+ do_div(ticks, 1000000000);
+ return ticks;
+}
+EXPORT_SYMBOL(pwm_ns_to_ticks);
+
+
+unsigned long pwm_ticks_to_ns(struct pwm_channel *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;
+}
+EXPORT_SYMBOL(pwm_ticks_to_ns);
+
+
+static void
+pwm_config_ns_to_ticks(struct pwm_channel *p,
+ struct pwm_channel_config *c)
+{
+ if (c->config_mask & PWM_CONFIG_PERIOD_NS) {
+ c->period_ticks = pwm_ns_to_ticks(p, c->period_ns);
+ c->config_mask &= ~PWM_CONFIG_PERIOD_NS;
+ c->config_mask |= PWM_CONFIG_PERIOD_TICKS;
+ }
+
+ if (c->config_mask & PWM_CONFIG_DUTY_NS) {
+ c->duty_ticks = pwm_ns_to_ticks(p, c->duty_ns);
+ c->config_mask &= ~PWM_CONFIG_DUTY_NS;
+ c->config_mask |= PWM_CONFIG_DUTY_TICKS;
+ }
+}
+
+
+static void
+pwm_config_percent_to_ticks(struct pwm_channel *p,
+ struct pwm_channel_config *c)
+{
+ if (c->config_mask & PWM_CONFIG_DUTY_PERCENT) {
+ if (c->config_mask & PWM_CONFIG_PERIOD_TICKS)
+ c->duty_ticks = c->period_ticks;
+ else
+ c->duty_ticks = p->period_ticks;
+
+ c->duty_ticks *= c->duty_percent;
+ c->duty_ticks /= 100;
+ c->config_mask &= ~PWM_CONFIG_DUTY_PERCENT;
+ c->config_mask |= PWM_CONFIG_DUTY_TICKS;
+ }
+}
+
+
+int pwm_config_nosleep(struct pwm_channel *p,
+ struct pwm_channel_config *c)
+{
+ if (!p->pwm->config_nosleep)
+ return -EINVAL;
+
+ pwm_config_ns_to_ticks(p, c);
+ pwm_config_percent_to_ticks(p, c);
+
+ return p->pwm->config_nosleep(p, c);
+}
+EXPORT_SYMBOL(pwm_config_nosleep);
+
+
+int pwm_config(struct pwm_channel *p,
+ struct pwm_channel_config *c)
+{
+ int ret = 0;
+
+ if (unlikely(!p->pwm->config)) {
+ pr_debug("%s: %s:%d has no config handler (-EINVAL)\n",
+ __func__, p->pwm->bus_id, p->chan);
+ return -EINVAL;
+ }
+
+ pwm_config_ns_to_ticks(p, c);
+ pwm_config_percent_to_ticks(p, c);
+
+ switch (c->config_mask & (PWM_CONFIG_PERIOD_TICKS
+ | PWM_CONFIG_DUTY_TICKS)) {
+ case PWM_CONFIG_PERIOD_TICKS:
+ if (p->duty_ticks > c->period_ticks) {
+ ret = -EINVAL;
+ goto err;
+ }
+ break;
+ case PWM_CONFIG_DUTY_TICKS:
+ if (p->period_ticks < c->duty_ticks) {
+ ret = -EINVAL;
+ goto err;
+ }
+ break;
+ case PWM_CONFIG_DUTY_TICKS | PWM_CONFIG_PERIOD_TICKS:
+ if (c->duty_ticks > c->period_ticks) {
+ ret = -EINVAL;
+ goto err;
+ }
+ break;
+ default:
+ break;
+ }
+
+err:
+ pr_debug("%s: config_mask %d period_ticks %lu duty_ticks %lu"
+ " polarity %d duty_ns %lu period_ns %lu duty_percent %d\n",
+ __func__, c->config_mask, c->period_ticks, c->duty_ticks,
+ c->polarity, c->duty_ns, c->period_ns, c->duty_percent);
+
+ if (ret)
+ return ret;
+ return p->pwm->config(p, c);
+}
+EXPORT_SYMBOL(pwm_config);
+
+
+int pwm_set_period_ns(struct pwm_channel *p,
+ unsigned long period_ns)
+{
+ struct pwm_channel_config c = {
+ .config_mask = 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_channel *p)
+{
+ return pwm_ticks_to_ns(p, p->period_ticks);
+}
+EXPORT_SYMBOL(pwm_get_period_ns);
+
+
+int pwm_set_duty_ns(struct pwm_channel *p,
+ unsigned long duty_ns)
+{
+ struct pwm_channel_config c = {
+ .config_mask = 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_channel *p)
+{
+ return pwm_ticks_to_ns(p, p->duty_ticks);
+}
+EXPORT_SYMBOL(pwm_get_duty_ns);
+
+
+int pwm_set_duty_percent(struct pwm_channel *p,
+ int percent)
+{
+ struct pwm_channel_config c = {
+ .config_mask = PWM_CONFIG_DUTY_PERCENT,
+ .duty_percent = percent,
+ };
+ return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_set_duty_percent);
+
+
+int pwm_set_polarity(struct pwm_channel *p,
+ int active_high)
+{
+ struct pwm_channel_config c = {
+ .config_mask = PWM_CONFIG_POLARITY,
+ .polarity = active_high,
+ };
+ return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_set_polarity);
+
+
+int pwm_start(struct pwm_channel *p)
+{
+ struct pwm_channel_config c = {
+ .config_mask = PWM_CONFIG_START,
+ };
+ return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_start);
+
+
+int pwm_stop(struct pwm_channel *p)
+{
+ struct pwm_channel_config c = {
+ .config_mask = PWM_CONFIG_STOP,
+ };
+ return pwm_config(p, &c);
+}
+EXPORT_SYMBOL(pwm_stop);
+
+
+int pwm_synchronize(struct pwm_channel *p,
+ struct pwm_channel *to_p)
+{
+ if (p->pwm != to_p->pwm) {
+ /* TODO: support cross-device synchronization */
+ return -EINVAL;
+ }
+
+ if (!p->pwm->synchronize)
+ return -EINVAL;
+
+ return p->pwm->synchronize(p, to_p);
+}
+EXPORT_SYMBOL(pwm_synchronize);
+
+
+int pwm_unsynchronize(struct pwm_channel *p,
+ struct pwm_channel *from_p)
+{
+ if (from_p && (p->pwm != from_p->pwm)) {
+ /* TODO: support cross-device synchronization */
+ return -EINVAL;
+ }
+
+ if (!p->pwm->unsynchronize)
+ return -EINVAL;
+
+ return p->pwm->unsynchronize(p, from_p);
+}
+EXPORT_SYMBOL(pwm_unsynchronize);
+
+
+static void pwm_handler(struct work_struct *w)
+{
+ struct pwm_channel *p = container_of(w, struct pwm_channel,
+ handler_work);
+ if (p->handler && p->handler(p, p->handler_data))
+ pwm_stop(p);
+}
+
+
+static void __pwm_callback(struct pwm_channel *p)
+{
+ queue_work(pwm_handler_workqueue, &p->handler_work);
+ pr_debug("%s:%d handler %p scheduled with data %p\n",
+ p->pwm->bus_id, p->chan, p->handler, p->handler_data);
+}
+
+
+int pwm_set_handler(struct pwm_channel *p,
+ pwm_handler_t handler,
+ void *data)
+{
+ if (p->pwm->set_callback) {
+ p->handler_data = data;
+ p->handler = handler;
+ INIT_WORK(&p->handler_work, pwm_handler);
+ return p->pwm->set_callback(p, handler ? __pwm_callback : NULL);
+ }
+ return -EINVAL;
+}
+EXPORT_SYMBOL(pwm_set_handler);
+
+
+static ssize_t pwm_run_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t len)
+{
+ struct pwm_channel *p = dev_get_drvdata(dev);
+ if (sysfs_streq(buf, "1"))
+ pwm_start(p);
+ else if (sysfs_streq(buf, "0"))
+ pwm_stop(p);
+ return len;
+}
+static DEVICE_ATTR(run, 0200, NULL, pwm_run_store);
+
+
+static ssize_t pwm_duty_ns_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct pwm_channel *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_channel *p = dev_get_drvdata(dev);
+
+ if (1 == sscanf(buf, "%lu", &duty_ns))
+ pwm_set_duty_ns(p, duty_ns);
+ return len;
+}
+static DEVICE_ATTR(duty_ns, 0644, 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_channel *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_channel *p = dev_get_drvdata(dev);
+
+ if (1 == sscanf(buf, "%lu", &period_ns))
+ pwm_set_period_ns(p, period_ns);
+ return len;
+}
+static DEVICE_ATTR(period_ns, 0644, 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_channel *p = dev_get_drvdata(dev);
+ return sprintf(buf, "%d\n", p->active_low ? 0 : 1);
+}
+
+
+static ssize_t pwm_polarity_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t len)
+{
+ int polarity;
+ struct pwm_channel *p = dev_get_drvdata(dev);
+
+ if (1 == sscanf(buf, "%d", &polarity))
+ pwm_set_polarity(p, polarity);
+ return len;
+}
+static DEVICE_ATTR(polarity, 0644, pwm_polarity_show, pwm_polarity_store);
+
+
+static ssize_t pwm_request_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct pwm_channel *p = dev_get_drvdata(dev);
+ mutex_lock(&device_list_mutex);
+ __pwm_request_channel(p, "sysfs");
+ mutex_unlock(&device_list_mutex);
+
+ return sprintf(buf, "%s\n", p->requester);
+}
+
+
+static ssize_t pwm_request_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t len)
+{
+ struct pwm_channel *p = dev_get_drvdata(dev);
+ pwm_free(p);
+ return len;
+}
+static DEVICE_ATTR(request, 0644, pwm_request_show, pwm_request_store);
+
+
+static const struct attribute *pwm_attrs[] =
+{
+ &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 int __pwm_create_sysfs(struct pwm_device *pwm)
+{
+ int ret = 0;
+ struct device *dev;
+ int wchan;
+
+ for (wchan = 0; wchan < pwm->nchan; wchan++) {
+ dev = device_create(&pwm_class, pwm->dev, MKDEV(0, 0),
+ pwm->channels + wchan,
+ "%s:%d", pwm->bus_id, wchan);
+ if (!dev)
+ goto err_dev_create;
+ ret = sysfs_create_group(&dev->kobj, &pwm_device_attr_group);
+ if (ret)
+ goto err_dev_group_create;
+ }
+
+ return ret;
+
+err_dev_group_create:
+err_dev_create:
+ /* TODO: undo all the successful device_create calls */
+ return -ENODEV;
+}
+
+
+static struct class_attribute pwm_class_attrs[] = {
+ __ATTR_NULL,
+};
+
+static struct class pwm_class = {
+ .name = "pwm",
+ .owner = THIS_MODULE,
+
+ .class_attrs = pwm_class_attrs,
+};
+
+
+static int __init pwm_init(void)
+{
+ int ret;
+
+ /* TODO: how to deal with devices that register very early? */
+
+ ret = class_register(&pwm_class);
+ if (ret < 0)
+ return ret;
+
+ pwm_handler_workqueue = create_workqueue("pwmd");
+
+ return 0;
+}
+postcore_initcall(pwm_init);
--
1.5.6.5
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