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

[Sven Van Asbroeck]

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@xxxxxxxxxxxxxxx>
Cc: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>
Cc: Uwe Kleine-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>
Cc: Clemens Gruber <clemens.gruber@xxxxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: linux-pwm@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/lkml/32ec35c2b3da119dd2c7bc09742796a0d8a9607e.camel@xxxxxxxxxxxxxxx/
Signed-off-by: Sven Van Asbroeck <TheSven73@xxxxxxxxx>
---

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