pwm: Add core infrastructure to allow atomic updates

Add an ->apply() method to the pwm_ops struct to allow PWM drivers to
implement atomic updates. This method is preferred over the ->enable(),
->disable() and ->config() methods if available.

Add the pwm_apply_state() function to the PWM user API.

Note that the pwm_apply_state() does not guarantee the atomicity of the
update operation, it all depends on the availability and implementation
of the ->apply() method.

pwm_enable/disable/set_polarity/config() are now implemented as wrappers
around the pwm_apply_state() function.

pwm_adjust_config() is allowing smooth handover between the bootloader
and the kernel. This function tries to adapt the current PWM state to
the PWM arguments coming from a PWM lookup table or a DT definition
without changing the duty_cycle/period proportion.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
[thierry.reding@gmail.com: fix a couple of typos]
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

2 files changed, 303 insertions, 153 deletions

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index a909c64ee863..729d457861fd 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -226,6 +226,19 @@ void *pwm_get_chip_data(struct pwm_device *pwm)
 }
 EXPORT_SYMBOL_GPL(pwm_get_chip_data);
 
+static bool pwm_ops_check(const struct pwm_ops *ops)
+{
+        /* driver supports legacy, non-atomic operation */
+        if (ops->config && ops->enable && ops->disable)
+                return true;
+
+        /* driver supports atomic operation */
+        if (ops->apply)
+                return true;
+
+        return false;
+}
+
 /**
  * pwmchip_add_with_polarity() - register a new PWM chip
  * @chip: the PWM chip to add
@@ -244,8 +257,10 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
         unsigned int i;
         int ret;
 
-        if (!chip || !chip->dev || !chip->ops || !chip->ops->config ||
-            !chip->ops->enable || !chip->ops->disable || !chip->npwm)
+        if (!chip || !chip->dev || !chip->ops || !chip->npwm)
+                return -EINVAL;
+
+        if (!pwm_ops_check(chip->ops))
                 return -EINVAL;
 
         mutex_lock(&pwm_lock);
@@ -431,102 +446,138 @@ void pwm_free(struct pwm_device *pwm)
 EXPORT_SYMBOL_GPL(pwm_free);
 
 /**
- * pwm_config() - change a PWM device configuration
+ * pwm_apply_state() - atomically apply a new state to a PWM device
  * @pwm: PWM device
- * @duty_ns: "on" time (in nanoseconds)
- * @period_ns: duration (in nanoseconds) of one cycle
- *
- * Returns: 0 on success or a negative error code on failure.
+ * @state: new state to apply. This can be adjusted by the PWM driver
+ *         if the requested config is not achievable, for example,
+ *         ->duty_cycle and ->period might be approximated.
  */
-int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
+int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state)
 {
         int err;
 
-        if (!pwm || duty_ns < 0 || period_ns <= 0 || duty_ns > period_ns)
+        if (!pwm)
                 return -EINVAL;
 
-        err = pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
-        if (err)
-                return err;
-
-        pwm->state.duty_cycle = duty_ns;
-        pwm->state.period = period_ns;
-
-        return 0;
-}
-EXPORT_SYMBOL_GPL(pwm_config);
+        if (!memcmp(state, &pwm->state, sizeof(*state)))
+                return 0;
 
-/**
- * pwm_set_polarity() - configure the polarity of a PWM signal
- * @pwm: PWM device
- * @polarity: new polarity of the PWM signal
- *
- * Note that the polarity cannot be configured while the PWM device is
- * enabled.
- *
- * Returns: 0 on success or a negative error code on failure.
- */
-int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
-{
-        int err;
+        if (pwm->chip->ops->apply) {
+                err = pwm->chip->ops->apply(pwm->chip, pwm, state);
+                if (err)
+                        return err;
 
-        if (!pwm || !pwm->chip->ops)
-                return -EINVAL;
+                pwm->state = *state;
+        } else {
+                /*
+                 * FIXME: restore the initial state in case of error.
+                 */
+                if (state->polarity != pwm->state.polarity) {
+                        if (!pwm->chip->ops->set_polarity)
+                                return -ENOTSUPP;
+
+                        /*
+                         * Changing the polarity of a running PWM is
+                         * only allowed when the PWM driver implements
+                         * ->apply().
+                         */
+                        if (pwm->state.enabled) {
+                                pwm->chip->ops->disable(pwm->chip, pwm);
+                                pwm->state.enabled = false;
+                        }
+
+                        err = pwm->chip->ops->set_polarity(pwm->chip, pwm,
+                                                           state->polarity);
+                        if (err)
+                                return err;
+
+                        pwm->state.polarity = state->polarity;
+                }
 
-        if (!pwm->chip->ops->set_polarity)
-                return -ENOSYS;
+                if (state->period != pwm->state.period ||
+                    state->duty_cycle != pwm->state.duty_cycle) {
+                        err = pwm->chip->ops->config(pwm->chip, pwm,
+                                                     state->duty_cycle,
+                                                     state->period);
+                        if (err)
+                                return err;
 
-        if (pwm_is_enabled(pwm))
-                return -EBUSY;
+                        pwm->state.duty_cycle = state->duty_cycle;
+                        pwm->state.period = state->period;
+                }
 
-        err = pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
-        if (err)
-                return err;
+                if (state->enabled != pwm->state.enabled) {
+                        if (state->enabled) {
+                                err = pwm->chip->ops->enable(pwm->chip, pwm);
+                                if (err)
+                                        return err;
+                        } else {
+                                pwm->chip->ops->disable(pwm->chip, pwm);
+                        }
 
-        pwm->state.polarity = polarity;
+                        pwm->state.enabled = state->enabled;
+                }
+        }
 
         return 0;
 }
-EXPORT_SYMBOL_GPL(pwm_set_polarity);
+EXPORT_SYMBOL_GPL(pwm_apply_state);
 
 /**
- * pwm_enable() - start a PWM output toggling
+ * pwm_adjust_config() - adjust the current PWM config to the PWM arguments
  * @pwm: PWM device
  *
- * Returns: 0 on success or a negative error code on failure.
+ * This function will adjust the PWM config to the PWM arguments provided
+ * by the DT or PWM lookup table. This is particularly useful to adapt
+ * the bootloader config to the Linux one.
  */
-int pwm_enable(struct pwm_device *pwm)
+int pwm_adjust_config(struct pwm_device *pwm)
 {
-        int err = 0;
+        struct pwm_state state;
+        struct pwm_args pargs;
 
-        if (!pwm)
-                return -EINVAL;
+        pwm_get_args(pwm, &pargs);
+        pwm_get_state(pwm, &state);
+
+        /*
+         * If the current period is zero it means that either the PWM driver
+         * does not support initial state retrieval or the PWM has not yet
+         * been configured.
+         *
+         * In either case, we setup the new period and polarity, and assign a
+         * duty cycle of 0.
+         */
+        if (!state.period) {
+                state.duty_cycle = 0;
+                state.period = pargs.period;
+                state.polarity = pargs.polarity;
 
-        if (!pwm_is_enabled(pwm)) {
-                err = pwm->chip->ops->enable(pwm->chip, pwm);
-                if (!err)
-                        pwm->state.enabled = true;
+                return pwm_apply_state(pwm, &state);
         }
 
-        return err;
-}
-EXPORT_SYMBOL_GPL(pwm_enable);
+        /*
+         * Adjust the PWM duty cycle/period based on the period value provided
+         * in PWM args.
+         */
+        if (pargs.period != state.period) {
+                u64 dutycycle = (u64)state.duty_cycle * pargs.period;
 
-/**
- * pwm_disable() - stop a PWM output toggling
- * @pwm: PWM device
- */
-void pwm_disable(struct pwm_device *pwm)
-{
-        if (!pwm)
-                return;
+                do_div(dutycycle, state.period);
+                state.duty_cycle = dutycycle;
+                state.period = pargs.period;
+        }
 
-        if (pwm_is_enabled(pwm)) {
-                pwm->chip->ops->disable(pwm->chip, pwm);
-                pwm->state.enabled = false;
+        /*
+         * If the polarity changed, we should also change the duty cycle.
+         */
+        if (pargs.polarity != state.polarity) {
+                state.polarity = pargs.polarity;
+                state.duty_cycle = state.period - state.duty_cycle;
         }
+
+        return pwm_apply_state(pwm, &state);
 }
-EXPORT_SYMBOL_GPL(pwm_disable);
+EXPORT_SYMBOL_GPL(pwm_adjust_config);
 
 static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
 {
diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 33f8decd9f38..17018f3c066e 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -5,59 +5,7 @@
 #include <linux/mutex.h>
 #include <linux/of.h>
 
-struct pwm_device;
 struct seq_file;
-
-#if IS_ENABLED(CONFIG_PWM)
-/*
- * pwm_request - request a PWM device
- */
-struct pwm_device *pwm_request(int pwm_id, const char *label);
-
-/*
- * pwm_free - free a PWM device
- */
-void pwm_free(struct pwm_device *pwm);
-
-/*
- * pwm_config - change a PWM device configuration
- */
-int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
-
-/*
- * pwm_enable - start a PWM output toggling
- */
-int pwm_enable(struct pwm_device *pwm);
-
-/*
- * pwm_disable - stop a PWM output toggling
- */
-void pwm_disable(struct pwm_device *pwm);
-#else
-static inline struct pwm_device *pwm_request(int pwm_id, const char *label)
-{
-        return ERR_PTR(-ENODEV);
-}
-
-static inline void pwm_free(struct pwm_device *pwm)
-{
-}
-
-static inline int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
-{
-        return -EINVAL;
-}
-
-static inline int pwm_enable(struct pwm_device *pwm)
-{
-        return -EINVAL;
-}
-
-static inline void pwm_disable(struct pwm_device *pwm)
-{
-}
-#endif
-
 struct pwm_chip;
 
 /**
@@ -184,11 +132,6 @@ static inline unsigned int pwm_get_duty_cycle(const struct pwm_device *pwm)
         return state.duty_cycle;
 }
 
-/*
- * pwm_set_polarity - configure the polarity of a PWM signal
- */
-int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity);
-
 static inline enum pwm_polarity pwm_get_polarity(const struct pwm_device *pwm)
 {
         struct pwm_state state;
@@ -204,34 +147,6 @@ static inline void pwm_get_args(const struct pwm_device *pwm,
         *args = pwm->args;
 }
 
-static inline void pwm_apply_args(struct pwm_device *pwm)
-{
-        /*
-         * PWM users calling pwm_apply_args() expect to have a fresh config
-         * where the polarity and period are set according to pwm_args info.
-         * The problem is, polarity can only be changed when the PWM is
-         * disabled.
-         *
-         * PWM drivers supporting hardware readout may declare the PWM device
-         * as enabled, and prevent polarity setting, which changes from the
-         * existing behavior, where all PWM devices are declared as disabled
-         * at startup (even if they are actually enabled), thus authorizing
-         * polarity setting.
-         *
-         * Instead of setting ->enabled to false, we call pwm_disable()
-         * before pwm_set_polarity() to ensure that everything is configured
-         * as expected, and the PWM is really disabled when the user request
-         * it.
-         *
-         * Note that PWM users requiring a smooth handover between the
-         * bootloader and the kernel (like critical regulators controlled by
-         * PWM devices) will have to switch to the atomic API and avoid calling
-         * pwm_apply_args().
-         */
-        pwm_disable(pwm);
-        pwm_set_polarity(pwm, pwm->args.polarity);
-}
-
 /**
  * struct pwm_ops - PWM controller operations
  * @request: optional hook for requesting a PWM
@@ -240,6 +155,10 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
  * @set_polarity: configure the polarity of this PWM
  * @enable: enable PWM output toggling
  * @disable: disable PWM output toggling
+ * @apply: atomically apply a new PWM config. The state argument
+ *         should be adjusted with the real hardware config (if the
+ *         approximate the period or duty_cycle value, state should
+ *         reflect it)
  * @get_state: get the current PWM state. This function is only
  *             called once per PWM device when the PWM chip is
  *             registered.
@@ -255,6 +174,8 @@ struct pwm_ops {
                             enum pwm_polarity polarity);
         int (*enable)(struct pwm_chip *chip, struct pwm_device *pwm);
         void (*disable)(struct pwm_chip *chip, struct pwm_device *pwm);
+        int (*apply)(struct pwm_chip *chip, struct pwm_device *pwm,
+                     struct pwm_state *state);
         void (*get_state)(struct pwm_chip *chip, struct pwm_device *pwm,
                           struct pwm_state *state);
 #ifdef CONFIG_DEBUG_FS
@@ -292,6 +213,115 @@ struct pwm_chip {
 };
 
 #if IS_ENABLED(CONFIG_PWM)
+/* PWM user APIs */
+struct pwm_device *pwm_request(int pwm_id, const char *label);
+void pwm_free(struct pwm_device *pwm);
+int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state);
+int pwm_adjust_config(struct pwm_device *pwm);
+
+/**
+ * pwm_config() - change a PWM device configuration
+ * @pwm: PWM device
+ * @duty_ns: "on" time (in nanoseconds)
+ * @period_ns: duration (in nanoseconds) of one cycle
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+static inline int pwm_config(struct pwm_device *pwm, int duty_ns,
+                             int period_ns)
+{
+        struct pwm_state state;
+
+        if (!pwm)
+                return -EINVAL;
+
+        pwm_get_state(pwm, &state);
+        if (state.duty_cycle == duty_ns && state.period == period_ns)
+                return 0;
+
+        state.duty_cycle = duty_ns;
+        state.period = period_ns;
+        return pwm_apply_state(pwm, &state);
+}
+
+/**
+ * pwm_set_polarity() - configure the polarity of a PWM signal
+ * @pwm: PWM device
+ * @polarity: new polarity of the PWM signal
+ *
+ * Note that the polarity cannot be configured while the PWM device is
+ * enabled.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+static inline int pwm_set_polarity(struct pwm_device *pwm,
+                                   enum pwm_polarity polarity)
+{
+        struct pwm_state state;
+
+        if (!pwm)
+                return -EINVAL;
+
+        pwm_get_state(pwm, &state);
+        if (state.polarity == polarity)
+                return 0;
+
+        /*
+         * Changing the polarity of a running PWM without adjusting the
+         * dutycycle/period value is a bit risky (can introduce glitches).
+         * Return -EBUSY in this case.
+         * Note that this is allowed when using pwm_apply_state() because
+         * the user specifies all the parameters.
+         */
+        if (state.enabled)
+                return -EBUSY;
+
+        state.polarity = polarity;
+        return pwm_apply_state(pwm, &state);
+}
+
+/**
+ * pwm_enable() - start a PWM output toggling
+ * @pwm: PWM device
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+static inline int pwm_enable(struct pwm_device *pwm)
+{
+        struct pwm_state state;
+
+        if (!pwm)
+                return -EINVAL;
+
+        pwm_get_state(pwm, &state);
+        if (state.enabled)
+                return 0;
+
+        state.enabled = true;
+        return pwm_apply_state(pwm, &state);
+}
+
+/**
+ * pwm_disable() - stop a PWM output toggling
+ * @pwm: PWM device
+ */
+static inline void pwm_disable(struct pwm_device *pwm)
+{
+        struct pwm_state state;
+
+        if (!pwm)
+                return;
+
+        pwm_get_state(pwm, &state);
+        if (!state.enabled)
+                return;
+
+        state.enabled = false;
+        pwm_apply_state(pwm, &state);
+}
+
+
+/* PWM provider APIs */
 int pwm_set_chip_data(struct pwm_device *pwm, void *data);
 void *pwm_get_chip_data(struct pwm_device *pwm);
 
@@ -317,6 +347,47 @@ void devm_pwm_put(struct device *dev, struct pwm_device *pwm);
 
 bool pwm_can_sleep(struct pwm_device *pwm);
 #else
+static inline struct pwm_device *pwm_request(int pwm_id, const char *label)
+{
+        return ERR_PTR(-ENODEV);
+}
+
+static inline void pwm_free(struct pwm_device *pwm)
+{
+}
+
+static inline int pwm_apply_state(struct pwm_device *pwm,
+                                  const struct pwm_state *state)
+{
+        return -ENOTSUPP;
+}
+
+static inline int pwm_adjust_config(struct pwm_device *pwm)
+{
+        return -ENOTSUPP;
+}
+
+static inline int pwm_config(struct pwm_device *pwm, int duty_ns,
+                             int period_ns)
+{
+        return -EINVAL;
+}
+
+static inline int pwm_set_polarity(struct pwm_device *pwm,
+                                   enum pwm_polarity polarity)
+{
+        return -ENOTSUPP;
+}
+
+static inline int pwm_enable(struct pwm_device *pwm)
+{
+        return -EINVAL;
+}
+
+static inline void pwm_disable(struct pwm_device *pwm)
+{
+}
+
 static inline int pwm_set_chip_data(struct pwm_device *pwm, void *data)
 {
         return -EINVAL;
@@ -388,6 +459,34 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
 }
 #endif
 
+static inline void pwm_apply_args(struct pwm_device *pwm)
+{
+        /*
+         * PWM users calling pwm_apply_args() expect to have a fresh config
+         * where the polarity and period are set according to pwm_args info.
+         * The problem is, polarity can only be changed when the PWM is
+         * disabled.
+         *
+         * PWM drivers supporting hardware readout may declare the PWM device
+         * as enabled, and prevent polarity setting, which changes from the
+         * existing behavior, where all PWM devices are declared as disabled
+         * at startup (even if they are actually enabled), thus authorizing
+         * polarity setting.
+         *
+         * Instead of setting ->enabled to false, we call pwm_disable()
+         * before pwm_set_polarity() to ensure that everything is configured
+         * as expected, and the PWM is really disabled when the user request
+         * it.
+         *
+         * Note that PWM users requiring a smooth handover between the
+         * bootloader and the kernel (like critical regulators controlled by
+         * PWM devices) will have to switch to the atomic API and avoid calling
+         * pwm_apply_args().
+         */
+        pwm_disable(pwm);
+        pwm_set_polarity(pwm, pwm->args.polarity);
+}
+
 struct pwm_lookup {
         struct list_head list;
         const char *provider;