In order to get rid of the global namespace for PWM devices, this commit
provides an alternative method, similar to that of the regulator or
clock frameworks, for registering a static mapping for PWM devices. This
works by providing a table with a provider/consumer map in the board
setup code.
With the new pwm_get() and pwm_put() functions available, usage of
pwm_request() and pwm_free() becomes deprecated.
Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxxxxxxxxxx>
---
Changes in v6:
- synchronize documentation with pwm_get() signature
- allow registering multiple PWM devices per user
Changes in v5:
- new patch with table-based lookup for statically registered devices
- update Documentation/pwm.txt
Documentation/pwm.txt | 27 ++++++--
drivers/pwm/core.c | 169 ++++++++++++++++++++++++++++++++++++++++++++-----
include/linux/pwm.h | 22 +++++++
3 files changed, 199 insertions(+), 19 deletions(-)
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index 48f598a..bb3d2f9 100644
--- a/Documentation/pwm.txt
+++ b/Documentation/pwm.txt
@@ -12,14 +12,33 @@ this kind of flexibility the generic PWM API exists.
Identifying PWMs
----------------
-Users of the legacy PWM API use unique IDs to refer to PWM devices. One
-goal of the new PWM framework is to get rid of this global namespace.
+Users of the legacy PWM API use unique IDs to refer to PWM devices.
+
+Instead of referring to a PWM device via its unique ID, board setup code
+should instead register a static mapping that can be used to match PWM
+consumers to providers, as given in the following example:
+
+ static struct pwm_lookup board_pwm_lookup[] = {
+ PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight"),
+ };
+
+ static void __init board_init(void)
+ {
+ ...
+ pwm_add_table(board_pwm_lookup, ARRAY_SIZE(board_pwm_lookup));
+ ...
+ }
Using PWMs
----------
-A PWM can be requested using pwm_request() and freed after usage with
-pwm_free(). After being requested a PWM has to be configured using
+Legacy users can request a PWM device using pwm_request() and free it
+after usage with pwm_free().
+
+New users should use the pwm_get() function and pass to it the consumer
+device or a consumer name. pwm_put() is used to free the PWM device.
+
+After being requested a PWM has to be configured using:
int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 7e13da1..402e466 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -32,6 +32,8 @@
#define MAX_PWMS 1024
+static DEFINE_MUTEX(pwm_lookup_lock);
+static LIST_HEAD(pwm_lookup_list);
static DEFINE_MUTEX(pwm_lock);
static LIST_HEAD(pwm_chips);
static DECLARE_BITMAP(allocated_pwms, MAX_PWMS);
@@ -80,6 +82,29 @@ static void free_pwms(struct pwm_chip *chip)
chip->pwms = NULL;
}
+static struct pwm_chip *pwmchip_find_by_name(const char *name)
+{
+ struct pwm_chip *chip;
+
+ if (!name)
+ return NULL;
+
+ mutex_lock(&pwm_lock);
+
+ list_for_each_entry(chip, &pwm_chips, list) {
+ const char *chip_name = dev_name(chip->dev);
+
+ if (chip_name && strcmp(chip_name, name) == 0) {
+ mutex_unlock(&pwm_lock);
+ return chip;
+ }
+ }
+
+ mutex_unlock(&pwm_lock);
+
+ return NULL;
+}
+
static int pwm_device_request(struct pwm_device *pwm, const char *label)
{
int err;
@@ -214,6 +239,8 @@ EXPORT_SYMBOL_GPL(pwmchip_remove);
* pwm_request() - request a PWM device
* @pwm_id: global PWM device index
* @label: PWM device label
+ *
+ * This function is deprecated, use pwm_get() instead.
*/
struct pwm_device *pwm_request(int pwm, const char *label)
{
@@ -277,24 +304,12 @@ EXPORT_SYMBOL_GPL(pwm_request_from_chip);
/**
* pwm_free() - free a PWM device
* @pwm: PWM device
+ *
+ * This function is deprecated, use pwm_put() instead.
*/
void pwm_free(struct pwm_device *pwm)
{
- mutex_lock(&pwm_lock);
-
- if (!test_and_clear_bit(PWMF_REQUESTED, &pwm->flags)) {
- pr_warning("PWM device already freed\n");
- goto out;
- }
-
- if (pwm->chip->ops->free)
- pwm->chip->ops->free(pwm->chip, pwm);
-
- pwm->label = NULL;
-
- module_put(pwm->chip->ops->owner);
-out:
- mutex_unlock(&pwm_lock);
+ pwm_put(pwm);
}
EXPORT_SYMBOL_GPL(pwm_free);
@@ -337,6 +352,130 @@ void pwm_disable(struct pwm_device *pwm)
}
EXPORT_SYMBOL_GPL(pwm_disable);
+/**
+ * pwm_add_table() - register PWM device consumers
+ * @table: array of consumers to register
+ * @num: number of consumers in table
+ */
+void __init pwm_add_table(struct pwm_lookup *table, size_t num)
+{
+ mutex_lock(&pwm_lookup_lock);
+
+ while (num--) {
+ list_add_tail(&table->list, &pwm_lookup_list);
+ table++;
+ }
+
+ mutex_unlock(&pwm_lookup_lock);
+}
+
+/**
+ * pwm_get() - look up and request a PWM device
+ * @dev: device for PWM consumer
+ * @con_id: consumer name
+ *
+ * Look up a PWM chip and a relative index via a table supplied by board setup
+ * code (see pwm_add_table()).
+ *
+ * Once a PWM chip has been found the specified PWM device will be requested
+ * and is ready to be used.
+ */
+struct pwm_device *pwm_get(struct device *dev, const char *con_id)
+{
+ struct pwm_device *pwm = ERR_PTR(-EPROBE_DEFER);
+ const char *dev_id = dev ? dev_name(dev): NULL;
+ struct pwm_chip *chip = NULL;
+ unsigned int best = 0;
+ struct pwm_lookup *p;
+ unsigned int index;
+ unsigned int match;
+
+ /*
+ * We look up the provider in the static table typically provided by
+ * board setup code. We first try to lookup the consumer device by
+ * name. If the consumer device was passed in as NULL or if no match
+ * was found, we try to find the consumer by directly looking it up
+ * by name.
+ *
+ * If a match is found, the provider PWM chip is looked up by name
+ * and a PWM device is requested using the PWM device per-chip index.
+ *
+ * The lookup algorithm was shamelessly taken from the clock
+ * framework:
+ *
+ * We do slightly fuzzy matching here:
+ * An entry with a NULL ID is assumed to be a wildcard.
+ * If an entry has a device ID, it must match
+ * If an entry has a connection ID, it must match
+ * Then we take the most specific entry - with the following order
+ * of precedence: dev+con > dev only > con only.
+ */
+ mutex_lock(&pwm_lookup_lock);
+
+ list_for_each_entry(p, &pwm_lookup_list, list) {
+ match = 0;
+
+ if (p->dev_id) {
+ if (!dev_id || strcmp(p->dev_id, dev_id))
+ continue;
+
+ match += 2;
+ }
+
+ if (p->con_id) {
+ if (!con_id || strcmp(p->con_id, con_id))
+ continue;
+
+ match += 1;
+ }
+
+ if (match > best) {
+ chip = pwmchip_find_by_name(p->provider);
+ index = p->index;
+
+ if (match != 3)
+ best = match;
+ else
+ break;
+ }
+ }
+
+ if (chip)
+ pwm = pwm_request_from_chip(chip, index, con_id ?: dev_id);
+
+ mutex_unlock(&pwm_lookup_lock);
+
+ return pwm;
+}
+EXPORT_SYMBOL_GPL(pwm_get);
+
+/**
+ * pwm_put() - release a PWM device
+ * @pwm: PWM device
+ */
+void pwm_put(struct pwm_device *pwm)
+{
+ if (!pwm)
+ return;
+
+ mutex_lock(&pwm_lock);
+
+ if (!test_and_clear_bit(PWMF_REQUESTED, &pwm->flags)) {
+ pr_warning("PWM device already freed\n");
+ goto out;
+ }
+
+ if (pwm->chip->ops->free)
+ pwm->chip->ops->free(pwm->chip, pwm);
+
+ pwm->label = NULL;
+
+ module_put(pwm->chip->ops->owner);
+out:
+ mutex_unlock(&pwm_lock);
+}
+EXPORT_SYMBOL_GPL(pwm_put);
+
#ifdef CONFIG_DEBUG_FS
static void pwm_dbg_show(struct pwm_chip *chip, struct seq_file *s)
{
diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 047cd53..2947a4f 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -115,6 +115,28 @@ int pwmchip_remove(struct pwm_chip *chip);
struct pwm_device *pwm_request_from_chip(struct pwm_chip *chip,
unsigned int index,
const char *label);
+
+struct pwm_device *pwm_get(struct device *dev, const char *consumer);
+void pwm_put(struct pwm_device *pwm);
+
+struct pwm_lookup {
+ struct list_head list;
+ const char *provider;
+ unsigned int index;
+ const char *dev_id;
+ const char *con_id;
+};
+
+#define PWM_LOOKUP(_provider, _index, _dev_id, _con_id) \
+ { \
+ .provider = _provider, \
+ .index = _index, \
+ .dev_id = _dev_id, \
+ .con_id = _con_id, \
+ }
+
+void pwm_add_table(struct pwm_lookup *table, size_t num);
+
#endif
#endif /* __LINUX_PWM_H */
--
1.7.9.6
--
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