linux-kernel - Re: [RESEND] i2c: mediatek: Get device clock-stretch time via dts

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Message-ID: <1618364244.32225.21.camel@mhfsdcap03>
Date:   Wed, 14 Apr 2021 09:37:24 +0800
From:   Qii Wang <qii.wang@...iatek.com>
To:     Wolfram Sang <wsa@...-dreams.de>
CC:     <matthias.bgg@...il.com>, <linux-i2c@...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>
Subject: Re: [RESEND] i2c: mediatek: Get device clock-stretch time via dts

On Tue, 2021-04-13 at 22:17 +0200, Wolfram Sang wrote:
> On Mon, Apr 12, 2021 at 08:03:14PM +0800, Qii Wang wrote:
> > I can't see the relationship between "i2c-scl-falling-time-ns" and clock
> > stretching, is there a parameter related to clock stretching?
> 
> ( you wrote "i2c-scl-falling-time-ns" above, didn't you mean
> "i2c-scl-internal-delay-ns" instead? )
> 

I am sorry, I have confused your comment with lkjoon's comment in the
last mail. what I actually want to say is "i2c-scl-internal-delay-ns".

> Not yet, and I wonder if there can be one. In I2C (not SMBus), devices
> are allowed to stretch the clock as long as they want, so what should be
> specified here?
> 
> I suggesteed "internal-delay" because AFAIU your hardware needs this
> delay to be able to cope with clock stretching.
> 

If there is not a maximum value for clock stretching,
"i2c-scl-internal-delay-ns" should be a good choice for our hardware,
although it maybe not for clock stretching.

> > If you think both of them will affect the ac-timing of SCL, at this
> > point, "i2c-scl-falling-time-ns" maybe a good choice.
> 
> Do you mean "i2c-scl-falling-time-ns" or "i2c-scl-internal-delay-ns"?
> 

"i2c-scl-internal-delay-ns" is better.

Thanks for your review.
Qii