linux-kernel - [PATCH] PWM: Add support for configuring polarity of PWM

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Date:	Wed, 18 Jul 2012 18:24:13 +0530
From:	"Philip, Avinash" <avinashphilip@...com>
To:	<thierry.reding@...onic-design.de>, <linux-kernel@...r.kernel.org>,
	<linux-omap@...r.kernel.org>
CC:	<nsekhar@...com>, <avinashphilip@...com>, <gururaja.hebbar@...com>
Subject: [PATCH] PWM: Add support for configuring polarity of PWM

Duty cycle inversion of PWM wave should achieved through PWM polarity
inversion. Also polarity of PWM wave should configurable from slave
drivers,

Configure polarity
1. PWM_POLARITY_NORMAL  -> duty ns defines ON period of PWM wave
2. PWM_POLARITY_INVERSE -> duty ns defines OFF period of PWM wave.

This patch adds support for configuring PWM polarity in PWM frame work.

Signed-off-by: Philip, Avinash <avinashphilip@...com>
---
Configuring polarity to be done with PWM device disabled, if not
failure reported.

If PWM device is enabled while configuring polarity, disabling and
re_enabling make it complex. Whoever uses this API has to taken
care of the basic rules.

Discussions related to this can found at
http://www.spinics.net/lists/kernel/msg1372110.html

:100644 100644 ecb7690... 24d5495... M	drivers/pwm/core.c
:100644 100644 21d076c... 2e4e960... M	include/linux/pwm.h
 drivers/pwm/core.c  |   32 ++++++++++++++++++++++++++++++++
 include/linux/pwm.h |   15 +++++++++++++++
 2 files changed, 47 insertions(+), 0 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index ecb7690..24d5495 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -379,6 +379,38 @@ int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
 EXPORT_SYMBOL_GPL(pwm_config);
 
 /**
+ * pwm_set_polarity() - change PWM device Polarity
+ * @pwm: PWM device
+ * @polarity: Configure polarity of PWM
+ *
+ * Polarity to be configured with PWM device disabled.
+ */
+int pwm_set_polarity(struct pwm_device *pwm, int polarity)
+{
+	int pwm_flags = PWM_POLARITY_NORMAL;
+
+	if (!pwm || !pwm->chip->ops->set_polarity)
+		return -EINVAL;
+
+	if (test_bit(PWMF_ENABLED, &pwm->flags)) {
+		dev_err(pwm->chip->dev,
+			"Polarity configuration Failed!, PWM device enabled\n");
+		return -EBUSY;
+	}
+
+	if (polarity == PWM_POLARITY_INVERSE)
+		pwm_flags = PWM_POLARITY_INVERSE;
+
+	if (!pwm_flags)
+		clear_bit(PWMF_POLARITY_INVERSE, &pwm->flags);
+	else
+		set_bit(PWMF_POLARITY_INVERSE, &pwm->flags);
+
+	return pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
+}
+EXPORT_SYMBOL_GPL(pwm_set_polarity);
+
+/**
  * pwm_enable() - start a PWM output toggling
  * @pwm: PWM device
  */
diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 21d076c..2e4e960 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -21,6 +21,16 @@ void pwm_free(struct pwm_device *pwm);
  */
 int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
 
+enum {
+	PWM_POLARITY_NORMAL,	/* ON period depends on duty_ns */
+	PWM_POLARITY_INVERSE,	/* OFF period depends on duty_ns */
+};
+
+/*
+ * pwm_set_polarity - set polarity of PWM device
+ */
+int pwm_set_polarity(struct pwm_device *pwm, int polarity);
+
 /*
  * pwm_enable - start a PWM output toggling
  */
@@ -37,6 +47,7 @@ struct pwm_chip;
 enum {
 	PWMF_REQUESTED = 1 << 0,
 	PWMF_ENABLED = 1 << 1,
+	PWMF_POLARITY_INVERSE = 1 << 2,
 };
 
 struct pwm_device {
@@ -66,6 +77,7 @@ static inline unsigned int pwm_get_period(struct pwm_device *pwm)
  * @request: optional hook for requesting a PWM
  * @free: optional hook for freeing a PWM
  * @config: configure duty cycles and period length for this PWM
+ * @set_polarity: configure polarity of PWM
  * @enable: enable PWM output toggling
  * @disable: disable PWM output toggling
  * @dbg_show: optional routine to show contents in debugfs
@@ -79,6 +91,9 @@ struct pwm_ops {
 	int			(*config)(struct pwm_chip *chip,
 					  struct pwm_device *pwm,
 					  int duty_ns, int period_ns);
+	int			(*set_polarity)(struct pwm_chip *chip,
+					  struct pwm_device *pwm,
+					  int polarity);
 	int			(*enable)(struct pwm_chip *chip,
 					  struct pwm_device *pwm);
 	void			(*disable)(struct pwm_chip *chip,
-- 
1.7.1

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