linux-kernel - Re: [v6, 3/3] reset-controller: ti: force the write operation when assert or deassert

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Date:   Wed, 2 Dec 2020 19:06:42 +0800
From:   Crystal Guo <crystal.guo@...iatek.com>
To:     Ikjoon Jang <ikjn@...omium.org>
CC:     "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Yong Liang (梁勇) 
        <Yong.Liang@...iatek.com>,
        Stanley Chu (朱原陞) 
        <stanley.chu@...iatek.com>,
        srv_heupstream <srv_heupstream@...iatek.com>,
        Seiya Wang (王迺君) 
        <seiya.wang@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Fan Chen (陳凡) 
        <fan.chen@...iatek.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Yingjoe Chen (陳英洲) 
        <Yingjoe.Chen@...iatek.com>, "s-anna@...com" <s-anna@...com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v6, 3/3] reset-controller: ti: force the write operation when
 assert or deassert

On Mon, 2020-11-30 at 19:13 +0800, Ikjoon Jang wrote:
> On Wed, Sep 30, 2020 at 10:21:59AM +0800, Crystal Guo wrote:
> > Force the write operation in case the read already happens
> > to return the correct value.
> > 
> > Signed-off-by: Crystal Guo <crystal.guo@...iatek.com>
> > ---
> >  drivers/reset/reset-ti-syscon.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/reset/reset-ti-syscon.c b/drivers/reset/reset-ti-syscon.c
> > index 5d1f8306cd4f..c34394f1e9e2 100644
> > --- a/drivers/reset/reset-ti-syscon.c
> > +++ b/drivers/reset/reset-ti-syscon.c
> > @@ -97,7 +97,7 @@ static int ti_syscon_reset_assert(struct reset_controller_dev *rcdev,
> >  	mask = BIT(control->assert_bit);
> >  	value = (control->flags & ASSERT_SET) ? mask : 0x0;
> >  
> > -	return regmap_update_bits(data->regmap, control->assert_offset, mask, value);
> > +	return regmap_write_bits(data->regmap, control->assert_offset, mask, value);
> >  }
> 
> I don't think there are no reset controllers with cached regmap,
> thus I don't think this is needed.
> Are there any specific reasons behind this, what I've missed here?
> 
> We need to be sure that all other devices using this driver
> should have no side effects on write.
> 
> I can think of a weird controller doing unwanted things internally
> on every write disregarding the current state. (or is this overly
> paranoid?)
> 
The specific reason is that, the clear bit may keep the same value with
the set bit, but the clear operation can be only be completed by writing
1 to the clear bit, not just with the current fake state "1".

> >  
> >  /**
> > @@ -128,7 +128,7 @@ static int ti_syscon_reset_deassert(struct reset_controller_dev *rcdev,
> >  	mask = BIT(control->deassert_bit);
> >  	value = (control->flags & DEASSERT_SET) ? mask : 0x0;
> >  
> > -	return regmap_update_bits(data->regmap, control->deassert_offset, mask, value);
> > +	return regmap_write_bits(data->regmap, control->deassert_offset, mask, value);
> >  }
> >  
> >  /**