linux-kernel - [PATCH 4.4 22/36] pwm: pca9685: Fix period change with same duty cycle

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Message-Id: <20170313083353.860036978@linuxfoundation.org>
Date:   Mon, 13 Mar 2017 16:39:22 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Clemens Gruber <clemens.gruber@...ruber.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Thierry Reding <thierry.reding@...il.com>
Subject: [PATCH 4.4 22/36] pwm: pca9685: Fix period change with same duty cycle

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Clemens Gruber <clemens.gruber@...ruber.com>

commit 8d254a340efb12b40c4c1ff25a48a4f48f7bbd6b upstream.

When first implementing support for changing the output frequency, an
optimization was added to continue the PWM after changing the prescaler
without having to reprogram the ON and OFF registers for the duty cycle,
in case the duty cycle stayed the same. This was flawed, because we
compared the absolute value of the duty cycle in nanoseconds instead of
the ratio to the period.

Fix the problem by removing the shortcut.

Fixes: 01ec8472009c9 ("pwm-pca9685: Support changing the output frequency")
Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
Signed-off-by: Thierry Reding <thierry.reding@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/pwm/pwm-pca9685.c |   11 -----------
 1 file changed, 11 deletions(-)

--- a/drivers/pwm/pwm-pca9685.c
+++ b/drivers/pwm/pwm-pca9685.c
@@ -65,7 +65,6 @@
 #define PCA9685_MAXCHAN		0x10
 
 #define LED_FULL		(1 << 4)
-#define MODE1_RESTART		(1 << 7)
 #define MODE1_SLEEP		(1 << 4)
 #define MODE2_INVRT		(1 << 4)
 #define MODE2_OUTDRV		(1 << 2)
@@ -117,16 +116,6 @@ static int pca9685_pwm_config(struct pwm
 			udelay(500);
 
 			pca->period_ns = period_ns;
-
-			/*
-			 * If the duty cycle did not change, restart PWM with
-			 * the same duty cycle to period ratio and return.
-			 */
-			if (duty_ns == pca->duty_ns) {
-				regmap_update_bits(pca->regmap, PCA9685_MODE1,
-						   MODE1_RESTART, 0x1);
-				return 0;
-			}
 		} else {
 			dev_err(chip->dev,
 				"prescaler not set: period out of bounds!\n");