linux-kernel - Re: [PATCH v3 2/6] pwm: mediatek: fix pwm source clock selection

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Message-ID: <d009712e-f0a2-2dc7-2f64-ad8cfa21f98d@gmail.com>
Date:   Wed, 5 Jul 2017 13:09:44 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Zhi Mao <zhi.mao@...iatek.com>, john@...ozen.org,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-pwm@...r.kernel.org
Cc:     srv_heupstream@...iatek.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, yingjoe.chen@...iatek.com,
        yt.shen@...iatek.com, sean.wang@...iatek.com,
        zhenbao.liu@...iatek.com
Subject: Re: [PATCH v3 2/6] pwm: mediatek: fix pwm source clock selection



On 06/30/2017 08:05 AM, Zhi Mao wrote:
> In original code, the pwm output frequency is not correct
> when set bit<3>=1 to PWMCON register.
> 
> Signed-off-by: Zhi Mao <zhi.mao@...iatek.com>
> ---
>   drivers/pwm/pwm-mediatek.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c
> index 5c11bc7..d08b5b3 100644
> --- a/drivers/pwm/pwm-mediatek.c
> +++ b/drivers/pwm/pwm-mediatek.c
> @@ -91,7 +91,7 @@ static int mtk_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>   	if (clkdiv > 7)
>   		return -EINVAL;
>   
> -	mtk_pwm_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | BIT(3) | clkdiv);
> +	mtk_pwm_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | clkdiv);

Just for clarification, BIT(15) enables old PWM mode, which ignores 
CLKSEL (BIT(3)). Therefore setting BIT(3) does not have any effect and 
can be discarded.

Am I correct? I took mt7623n datasheet for reference.

Regards,
Matthias

>   	mtk_pwm_writel(pc, pwm->hwpwm, PWMDWIDTH, period_ns / resolution);
>   	mtk_pwm_writel(pc, pwm->hwpwm, PWMTHRES, duty_ns / resolution);
>   
>