[PATCH] pwm: meson: fix harware duty calculation

[PATCH] pwm: meson: fix harware duty calculation

[Yixun Lan]

From: Jian Hu <jian.hu@amlogic.com>

The actual HIGH/LOW signal output from the PWM is equal to
the value programed to HW register plus one, this is designed by HW.

This fix should apply to all Meson SoC(include GX/GXL/GXBB, Meson6,8)

Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller")
Signed-off-by: Jian Hu <jian.hu@amlogic.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
---
 drivers/pwm/pwm-meson.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index d589331d1884..78d9b8c1a4bc 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -193,6 +193,11 @@ static int meson_pwm_calc(struct meson_pwm *meson,
 			break;
 	}
 
+	if (cnt < 2) {
+		dev_err(meson->chip.dev, "invalid period\n");
+		return -EINVAL;
+	}
+
 	if (pre_div == MISC_CLK_DIV_MASK) {
 		dev_err(meson->chip.dev, "unable to get period pre_div\n");
 		return -EINVAL;
@@ -201,19 +206,23 @@ static int meson_pwm_calc(struct meson_pwm *meson,
 	dev_dbg(meson->chip.dev, "period=%u pre_div=%u cnt=%u\n", period,
 		pre_div, cnt);
 
+	/*
+	 * Due to the design of hardware, values of 'hi', 'lo' are 1 based
+	 * which mean the actual output from hardware is 'hi' + 1, 'lo' + 1
+	 */
 	if (duty == period) {
 		channel->pre_div = pre_div;
-		channel->hi = cnt;
+		channel->hi = cnt - 1;
 		channel->lo = 0;
 	} else if (duty == 0) {
 		channel->pre_div = pre_div;
 		channel->hi = 0;
-		channel->lo = cnt;
+		channel->lo = cnt - 1;
 	} else {
 		/* Then check is we can have the duty with the same pre_div */
 		duty_cnt = DIV_ROUND_CLOSEST_ULL((u64)duty * 1000,
 						 fin_ps * (pre_div + 1));
-		if (duty_cnt > 0xffff) {
+		if (duty_cnt > 0xffff || !duty_cnt) {
 			dev_err(meson->chip.dev, "unable to get duty cycle\n");
 			return -EINVAL;
 		}
@@ -222,8 +231,8 @@ static int meson_pwm_calc(struct meson_pwm *meson,
 			duty, pre_div, duty_cnt);
 
 		channel->pre_div = pre_div;
-		channel->hi = duty_cnt;
-		channel->lo = cnt - duty_cnt;
+		channel->hi = duty_cnt - 1;
+		channel->lo = cnt - duty_cnt - 1;
 	}
 
 	return 0;
-- 
2.15.0

Re: [PATCH] pwm: meson: fix harware duty calculation

[Jerome Brunet]

On Wed, 2017-11-29 at 11:03 +0800, Yixun Lan wrote:
> From: Jian Hu <jian.hu@amlogic.com>
> 
> The actual HIGH/LOW signal output from the PWM is equal to
> the value programed to HW register plus one, this is designed by HW.
> 
> This fix should apply to all Meson SoC(include GX/GXL/GXBB, Meson6,8)
> 
> Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller")
> Signed-off-by: Jian Hu <jian.hu@amlogic.com>
> Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
> ---
>  drivers/pwm/pwm-meson.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
> index d589331d1884..78d9b8c1a4bc 100644
> --- a/drivers/pwm/pwm-meson.c
> +++ b/drivers/pwm/pwm-meson.c
> @@ -193,6 +193,11 @@ static int meson_pwm_calc(struct meson_pwm *meson,
>  			break;
>  	}
>  
> +	if (cnt < 2) {
> +		dev_err(meson->chip.dev, "invalid period\n");
> +		return -EINVAL;
> +	}
> +
>  	if (pre_div == MISC_CLK_DIV_MASK) {
>  		dev_err(meson->chip.dev, "unable to get period pre_div\n");
>  		return -EINVAL;
> @@ -201,19 +206,23 @@ static int meson_pwm_calc(struct meson_pwm *meson,
>  	dev_dbg(meson->chip.dev, "period=%u pre_div=%u cnt=%u\n", period,
>  		pre_div, cnt);
>  
> +	/*
> +	 * Due to the design of hardware, values of 'hi', 'lo' are 1 based
> +	 * which mean the actual output from hardware is 'hi' + 1, 'lo' + 1
> +	 */
>  	if (duty == period) {
>  		channel->pre_div = pre_div;
> -		channel->hi = cnt;
> +		channel->hi = cnt - 1;
>  		channel->lo = 0;
>  	} else if (duty == 0) {
>  		channel->pre_div = pre_div;
>  		channel->hi = 0;
> -		channel->lo = cnt;
> +		channel->lo = cnt - 1;
>  	} else {
>  		/* Then check is we can have the duty with the same pre_div
> */
>  		duty_cnt = DIV_ROUND_CLOSEST_ULL((u64)duty * 1000,
>  						 fin_ps * (pre_div + 1));
> -		if (duty_cnt > 0xffff) {
> +		if (duty_cnt > 0xffff || !duty_cnt) {

duty_cnt = 0 is a valid value here. It will be the case for duty != 0 but low
enough for the HW (calculation) to approximate the duty cycle to zero.

>  			dev_err(meson->chip.dev, "unable to get duty
> cycle\n");
>  			return -EINVAL;
>  		}
> @@ -222,8 +231,8 @@ static int meson_pwm_calc(struct meson_pwm *meson,
>  			duty, pre_div, duty_cnt);
>  
>  		channel->pre_div = pre_div;
> -		channel->hi = duty_cnt;
> -		channel->lo = cnt - duty_cnt;
> +		channel->hi = duty_cnt - 1;

As explained above, duty_cnt could be zero, you need to take care of this here

> +		channel->lo = cnt - duty_cnt - 1;

Same here, it is possible duty_cnt to be egual to cnt so you also need to be
careful here

>  	}
>  
>  	return 0;