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")
Cc: <[email protected]> # v4.3+
Signed-off-by: Clemens Gruber <[email protected]>
---
drivers/pwm/pwm-pca9685.c | 11 -----------
1 file changed, 11 deletions(-)
diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
index 117fccf..01a6a83 100644
--- 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_chip *chip, struct pwm_device *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");
--
2.10.2
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: <[email protected]> # v4.3+
Signed-off-by: Clemens Gruber <[email protected]>
---
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