linux-kernel - Re: [PATCH v7 6/7] i2c: mediatek: Isolate speed setting via dts for special devices

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Date:   Fri, 8 Oct 2021 16:47:11 +0800
From:   Kewei Xu <kewei.xu@...iatek.com>
To:     Wolfram Sang <wsa@...-dreams.de>
CC:     <matthias.bgg@...il.com>, <robh+dt@...nel.org>,
        <linux-i2c@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>, <leilk.liu@...iatek.com>,
        <qii.wang@...iatek.com>, <liguo.zhang@...iatek.com>,
        <caiyu.chen@...iatek.com>, <ot_daolong.zhu@...iatek.com>,
        <yuhan.wei@...iatek.com>
Subject: Re: [PATCH v7 6/7] i2c: mediatek: Isolate speed setting via dts for
 special devices

On Sat, 2021-10-02 at 08:40 +0200, Wolfram Sang wrote:
> On Fri, Sep 17, 2021 at 06:14:15PM +0800, Kewei Xu wrote:
> > In the commit be5ce0e97cc7 ("i2c: mediatek: Add i2c ac-timing
> > adjust
> > support"), the I2C timing calculation has been revised to support
> > ac-timing adjustment, however that will break on some I2C
> > components.
> > As a result we want to introduce a new setting "default-adjust-
> > timing"
> > so those components can choose to use the old (default) timing
> > algorithm.
> 
> Why can't the new calculation be updated in a way that it works for
> all
> I2C components?
> 
Hi, In the commit be5ce0e97cc7 ("i2c: mediatek: Add i2c ac-timing
adjust support"), the I2C timing calculation has been revised to
support ac-timing adjustment.But in our design, it will make
tSU,STA/tHD,STA/tSU,STO shorter when the slave device have clock-
stretching feature. Then we upload the commit a80f24945fcf ("i2c:
mediatek: Use scl_int_delay_ns to compensate clock-stretching") to
support adjusting tSU,STA/tHD,STA/tSU,STO when the slave device clock-
stretching. But if the slave device stretch the SCL line for too long
time, our design still cannot make tSU,STA/tHD,STA/tSU,STO meet spec.
However in the old (default) timing algorithm before the commit
be5ce0e97cc7 ("i2c: mediatek: Add i2c ac-timing adjust support"),
tSU,STA/tHD,STA/tSU,STO can meet spec. So we want to define a new
setting "default-adjust-timing" for using the old (default) timing
algorithm. Thanks~