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Subject[PATCH 2/2] pwm: pca9685: fix prescaler initialization
Date
Until now, we assumed that the period is the hardware default of 1/200Hz
at probe time, but if the period was changed and the user reboots, this
assumption is wrong.

Solution: Check if the prescaler is set to the hardware default. If not,
reprogram the prescaler at first configuration.

Cc: <stable@vger.kernel.org> # v4.3+
Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
---
drivers/pwm/pwm-pca9685.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
index 01a6a83..efc657e 100644
--- a/drivers/pwm/pwm-pca9685.c
+++ b/drivers/pwm/pwm-pca9685.c
@@ -55,6 +55,7 @@
#define PCA9685_PRESCALE 0xFE

#define PCA9685_PRESCALE_MIN 0x03 /* => max. frequency of 1526 Hz */
+#define PCA9685_PRESCALE_DEF 0x1E /* => default frequency of 200 Hz */
#define PCA9685_PRESCALE_MAX 0xFF /* => min. frequency of 24 Hz */

#define PCA9685_COUNTER_RANGE 4096
@@ -289,8 +290,8 @@ static int pca9685_pwm_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
struct pca9685 *pca;
+ int prescale, mode2;
int ret;
- int mode2;

pca = devm_kzalloc(&client->dev, sizeof(*pca), GFP_KERNEL);
if (!pca)
@@ -304,10 +305,15 @@ static int pca9685_pwm_probe(struct i2c_client *client,
return ret;
}
pca->duty_ns = 0;
- pca->period_ns = PCA9685_DEFAULT_PERIOD;

i2c_set_clientdata(client, pca);

+ regmap_read(pca->regmap, PCA9685_PRESCALE, &prescale);
+ if (prescale == PCA9685_PRESCALE_DEF)
+ pca->period_ns = PCA9685_DEFAULT_PERIOD;
+ else
+ pca->period_ns = 0;
+
regmap_read(pca->regmap, PCA9685_MODE2, &mode2);

if (device_property_read_bool(&client->dev, "invert"))
--
2.10.2
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