npcx: pwm: Use DCRn greater than CTRn to present its duty cycle is zero.

In npcx pwm driver, it turns off pwm module directly when its duty cycle
is set to zero. But we saw pwm signal isn't turned off by the following
sequence:
1. pwm_set_raw_duty(ch, 0);
2. pwm_enable(ch, 1);

Please notice setting zero in DCRn doesn't mean duty cycle is zero.
(NPCX duty cycle: ( (DCRn+1) / (CTRn+1) ) x 100). Hence in step 2, we
can observe a very low duty cycle once the driver enables pwm module.

According to figure. 24 in npcx5's datasheet, setting DCRn greater than
CTRn means that the result of 16-bits comparator is always false. It
equals the duty cycle is zero. This CL adopts this method to present it
and removes the dependency between pwm_enable()/ pwm_get_enabled() and
pwm_set_raw_duty()/pwm_get_duty().

In order to make sure DCRn can be greater than CTRn, we also defined
the PWN maximum duty cycle is (0xFFFF -1) since both DCR and CTR are
16-bits registers.

BRANCH=none
BUG=b:123552920
TEST=No build errors for npcx5/7 series.

Test pwm console command on npcx5/7 evbs by the following sequence.
1. pwm_set_raw_duty(ch, 0);
2. pwm_enable(ch, 1);
And no symptoms are observed. PWM_CONFIG_ACTIVE_LOW flag is tested also
and no symptom occurred.

Test fan control by faninfo & fanset console commands. Connect Sunon
4-pins PWM fan and evb by following steps:
1. Connect PWM0 to PWM pin of fan.
2. Connect TA1_TACH1 and 3.3 PU on Tacho pin of fan.
3. Connect 5V and GND pins of fan to power supply.
No symptoms are observed.

Change-Id: I92517ff0bf3e027ae191be00112cd71ec4b55a2b
Signed-off-by: Mulin Chao <mlchao@nuvoton.com>
Reviewed-on: https://chromium-review.googlesource.com/1475096
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>

1 files changed, 0 insertions, 6 deletions

diff --git a/include/pwm.h b/include/pwm.h
index 24b89332fc..15413c537c 100644
--- a/include/pwm.h
+++ b/include/pwm.h
@@ -20,12 +20,6 @@ void pwm_enable(enum pwm_channel ch, int enabled);
 int pwm_get_enabled(enum pwm_channel ch);
 
 /**
- * Set PWM channel frequency (Hz).
- * PWM will be disabled until the duty is set.
- */
-void pwm_set_freq(enum pwm_channel ch, uint32_t freq);
-
-/**
  * Set PWM channel duty cycle (0-65535).
  */
 void pwm_set_raw_duty(enum pwm_channel ch, uint16_t duty);