pwm: Add table-based lookup for static mappings

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.

Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>

3 files changed, 199 insertions, 19 deletions

diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index 48f598acdd16..554290ebab94 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", NULL),
+        };
+
+        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 aadc1d797449..a2af599e61ae 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;
@@ -218,6 +243,8 @@ 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)
 {
@@ -281,24 +308,12 @@ 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);
 
@@ -341,6 +356,130 @@ 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 047cd5351a3b..2947a4fea6ad 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 */