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

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Message-ID: <1499321801.22478.12.camel@mhfsdcap03>
Date:   Thu, 6 Jul 2017 14:16:41 +0800
From:   Zhi Mao <zhi.mao@...iatek.com>
To:     Matthias Brugger <matthias.bgg@...il.com>
CC:     <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>, <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 Wed, 2017-07-05 at 13:09 +0200, Matthias Brugger wrote:
> 
> 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
> 
Yes, remove setting bit<3> will not take any effect. 
PWMCON bit<3> is pwm source clock selecting register.
You can check the datasheet of MT7623 for details.

Regards
Zhi

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