diff options
| -rw-r--r-- | drivers/pwm/pwm-jz4740.c | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c index 4fe9d99ac9a9..fe06ca8ce30f 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -6,7 +6,6 @@ * Limitations: * - The .apply callback doesn't complete the currently running period before * reconfiguring the hardware. - * - Each period starts with the inactive part. */ #include <linux/clk.h> @@ -163,7 +162,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, /* Calculate duty value */ tmp = (unsigned long long)rate * state->duty_cycle; do_div(tmp, NSEC_PER_SEC); - duty = period - tmp; + duty = tmp; if (duty >= period) duty = period - 1; @@ -189,18 +188,26 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD); - /* Set polarity */ - switch (state->polarity) { - case PWM_POLARITY_NORMAL: + /* + * Set polarity. + * + * The PWM starts in inactive state until the internal timer reaches the + * duty value, then becomes active until the timer reaches the period + * value. In theory, we should then use (period - duty) as the real duty + * value, as a high duty value would otherwise result in the PWM pin + * being inactive most of the time. + * + * Here, we don't do that, and instead invert the polarity of the PWM + * when it is active. This trick makes the PWM start with its active + * state instead of its inactive state. + */ + if ((state->polarity == PWM_POLARITY_NORMAL) ^ state->enabled) regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_INITL_HIGH, 0); - break; - case PWM_POLARITY_INVERSED: + else regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_INITL_HIGH, TCU_TCSR_PWM_INITL_HIGH); - break; - } if (state->enabled) jz4740_pwm_enable(chip, pwm); |