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

This is a reland of 93d7bcea8121869520b0d02bf94f95eb261bee05 with a fix
for fan_is_stalled.

Original change's description:
> 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>

Bug: b:123552920
Change-Id: I4ea76c51811507ee4a35e5c0edfb70e9fb6c4c8b
Reviewed-on: https://chromium-review.googlesource.com/1506115
Commit-Ready: Daisuke Nojiri <dnojiri@chromium.org>
Tested-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
(cherry picked from commit e5d249549b0cfc761fd81d8eb596bc05da629e1f)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1514978
Commit-Queue: Daisuke Nojiri <dnojiri@chromium.org>

4 files changed, 14 insertions, 26 deletions

diff --git a/chip/npcx/fan.c b/chip/npcx/fan.c
index c14d4e20ed..2116dfebc7 100644
--- a/chip/npcx/fan.c
+++ b/chip/npcx/fan.c
@@ -519,11 +519,8 @@ enum fan_status fan_get_status(int ch)
  */
 int fan_is_stalled(int ch)
 {
-	/* if fan is enabled but we didn't detect any tacho */
-	if (fan_get_enabled(ch) && fan_status[ch].cur_state == TACHO_UNDERFLOW)
-		return 1;
-	else
-		return 0;
+	return fan_get_enabled(ch) && fan_get_duty(ch) &&
+			fan_status[ch].cur_state == TACHO_UNDERFLOW;
 }
 
 /**
diff --git a/chip/npcx/pwm.c b/chip/npcx/pwm.c
index b452b00beb..13af516bb9 100644
--- a/chip/npcx/pwm.c
+++ b/chip/npcx/pwm.c
@@ -55,7 +55,7 @@ enum npcx_pwm_heartbeat_mode {
  * @param   freq    desired PWM frequency
  * @notes   changed when initialization
  */
-void pwm_set_freq(enum pwm_channel ch, uint32_t freq)
+static void pwm_set_freq(enum pwm_channel ch, uint32_t freq)
 {
 	int mdl = pwm_channels[ch].channel;
 	uint32_t clock;
@@ -78,8 +78,11 @@ void pwm_set_freq(enum pwm_channel ch, uint32_t freq)
 	/* Calculate prescaler */
 	pre = DIV_ROUND_UP(clock, (0xffff * freq));
 
-	/* Calculate maximum resolution for the given freq. and prescaler */
-	pwm_res[ch] = (clock / pre) / freq;
+	/*
+	 * Calculate maximum resolution for the given freq. and prescaler. And
+	 * prevent it exceed the resolution of CTR/DCR registers.
+	 */
+	pwm_res[ch] = MIN((clock / pre) / freq, NPCX_PWM_MAX_RAW_DUTY);
 
 	/* Set PWM prescaler. */
 	NPCX_PRSC(mdl) = pre - 1;
@@ -96,7 +99,6 @@ void pwm_set_freq(enum pwm_channel ch, uint32_t freq)
  *
  * @param   ch      operation channel
  * @param   enabled enabled flag
- * @return  none
  */
 void pwm_enable(enum pwm_channel ch, int enabled)
 {
@@ -123,7 +125,6 @@ int pwm_get_enabled(enum pwm_channel ch)
  *
  * @param   ch      operation channel
  * @param   percent duty cycle percent
- * @return  none
  */
 void pwm_set_duty(enum pwm_channel ch, int percent)
 {
@@ -136,7 +137,6 @@ void pwm_set_duty(enum pwm_channel ch, int percent)
  *
  * @param   ch      operation channel
  * @param   duty    cycle duty
- * @return  none
  */
 void pwm_set_raw_duty(enum pwm_channel ch, uint16_t duty)
 {
@@ -155,10 +155,8 @@ void pwm_set_raw_duty(enum pwm_channel ch, uint16_t duty)
 	/* duty ranges from 0 - 0xffff, so scale down to 0 - pwm_res[ch] */
 	sd = DIV_ROUND_NEAREST(duty * pwm_res[ch], EC_PWM_MAX_DUTY);
 
-	/* Set the duty cycle */
-	NPCX_DCR(mdl) = (uint16_t)sd;
-
-	pwm_enable(ch, !!duty);
+	/* Set the duty cycle. If it is zero, set DCR > CTR */
+	NPCX_DCR(mdl) = sd ? sd : NPCX_PWM_MAX_RAW_DUTY + 1;
 }
 
 /**
@@ -184,7 +182,7 @@ uint16_t pwm_get_raw_duty(enum pwm_channel ch)
 	int mdl = pwm_channels[ch].channel;
 
 	/* Return duty */
-	if (!pwm_get_enabled(ch))
+	if (NPCX_DCR(mdl) > NPCX_CTR(mdl))
 		return 0;
 	else
 		/*
@@ -199,7 +197,6 @@ uint16_t pwm_get_raw_duty(enum pwm_channel ch)
  * PWM configuration.
  *
  * @param  ch    operation channel
- * @return none
  */
 void pwm_config(enum pwm_channel ch)
 {
@@ -233,9 +230,6 @@ void pwm_config(enum pwm_channel ch)
 
 /**
  * PWM initial.
- *
- * @param none
- * @return none
  */
 static void pwm_init(void)
 {
diff --git a/chip/npcx/pwm_chip.h b/chip/npcx/pwm_chip.h
index c73855916f..3a658f5d62 100644
--- a/chip/npcx/pwm_chip.h
+++ b/chip/npcx/pwm_chip.h
@@ -21,4 +21,7 @@ struct pwm_t {
 extern const struct pwm_t pwm_channels[];
 void pwm_config(enum pwm_channel ch);
 
+/* Npcx PWM maximum duty cycle value */
+#define NPCX_PWM_MAX_RAW_DUTY (UINT16_MAX - 1)
+
 #endif /* __CROS_EC_PWM_CHIP_H */
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);