[PATCH v5 20/24] pwm: add the PWM initial state retrieval infra

Boris Brezillon
2016-04-14T19:17:40Z

Add a ->get_state() function to the pwm_ops struct to let PWM drivers
initialize the PWM state attached to a PWM device.

Signed-off-by: Boris Brezillon <boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
---
drivers/pwm/core.c | 3 +++
include/linux/pwm.h | 28 ++++++++++++++++++++++++++++
2 files changed, 31 insertions(+)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index c2759bc..0e7f687 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -270,6 +270,9 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
pwm->hwpwm = i;
pwm->state.polarity = polarity;

+ if (chip->ops->get_state)
+ chip->ops->get_state(chip, pwm, &pwm->state);
+
radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
}

diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 7bfeacf..73ca679 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -205,6 +205,29 @@ static inline void pwm_get_args(const struct pwm_device *pwm,

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);
}

@@ -216,6 +239,9 @@ 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
+ * @get_state: get the current PWM state. This function is only
+ * called once per PWM device when the PWM chip is
+ * registered.
* @dbg_show: optional routine to show contents in debugfs
* @owner: helps prevent removal of modules exporting active PWMs
*/
@@ -228,6 +254,8 @@ 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);
+ void (*get_state)(struct pwm_chip *chip, struct pwm_device *pwm,
+ struct pwm_state *state);
#ifdef CONFIG_DEBUG_FS
void (*dbg_show)(struct pwm_chip *chip, struct seq_file *s);
#endif
--
2.5.0