linux-kernel - [PATCH v1] pwm: pca9685: re-enable active pwm channels on pwm period change

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Date:   Fri,  3 Apr 2020 19:53:24 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Clemens Gruber <clemens.gruber@...ruber.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] pwm: pca9685: re-enable active pwm channels on pwm period change

In order to change the pwm period, this chip must be put in sleep
mode. However, when coming out of sleep mode, the pwm channel
state is not completely restored: all pwm channels are off by
default.

This results in a bug in this driver: when the pwm period is changed
on a pwm channel, all other pwm channels will be deactivated.

Fix by clearing the RESTART bit when coming out of sleep mode - this
will restore all pwm channels to their pre-sleep on/off state.

Reported-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc: Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: Clemens Gruber <clemens.gruber@...ruber.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: linux-pwm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Link: https://lore.kernel.org/lkml/32ec35c2b3da119dd2c7bc09742796a0d8a9607e.camel@ew.tq-group.com/
Signed-off-by: Sven Van Asbroeck <TheSven73@...il.com>
---

I no longer have access to pca9685 hardware, so I'm unable to test:
- if this is indeed a bug
- if this patch fixes it

Made against:
Tree-repo: git.kernel.org/pub/scm/linux/kernel/git/thierry.reding/linux-pwm.git
Tree-branch: for-next
Tree-git-id: 9cc5f232a4b6a0ef6e9b57876d61b88f61bdd7c2

 drivers/pwm/pwm-pca9685.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
index 76cd22bd6614..0a16f0122e0e 100644
--- a/drivers/pwm/pwm-pca9685.c
+++ b/drivers/pwm/pwm-pca9685.c
@@ -59,6 +59,7 @@
 
 #define LED_FULL		(1 << 4)
 #define MODE1_SLEEP		(1 << 4)
+#define MODE1_RESTART		(1 << 7)
 #define MODE2_INVRT		(1 << 4)
 #define MODE2_OUTDRV		(1 << 2)
 
@@ -271,6 +272,15 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 			/* Wake the chip up */
 			pca9685_set_sleep_mode(pca, false);
 
+			/* If any pwm channels were active when the chip was put
+			 * in sleep mode, re-activate them.
+			 */
+			if (!regmap_read(pca->regmap, PCA9685_MODE1, &reg) &&
+			    reg & MODE1_RESTART)
+				regmap_update_bits(pca->regmap, PCA9685_MODE1,
+						   MODE1_RESTART,
+						   MODE1_RESTART);
+
 			pca->period_ns = period_ns;
 		} else {
 			dev_err(chip->dev,
-- 
2.17.1