linux-kernel - Re: [PATCH v5 2/8] i2c: iproc: Add slave mode support

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Date:   Tue, 2 Apr 2019 11:01:05 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
Cc:     Ray Jui <ray.jui@...adcom.com>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        Shreesha Rajashekar <shreesha.rajashekar@...adcom.com>,
        Michael Cheng <ccheng@...adcom.com>
Subject: Re: [PATCH v5 2/8] i2c: iproc: Add slave mode support


> > >> +    /* RANDOM SLAVE STRETCH time - 20ms*/
> > >
> > > What is a "random stretch time"? 20ms sounds like a lot. Also, missing
> > > space before comment terminator.
> > >
> >
> > Rayagonda,
> >
> > Could you please help to comment on the choice of the 20 ms to allow
> > clock stretch from the slave? In probably all cases, the slave should
> > not need more than 1 ms? 20 ms does seem way too long as Wolfram pointed
> > out.
> 
> In fact we are programming max slave stretch time  ie 25ms, comment
> should be correcting.
> Its maximum time for slave to complete read/write operation, if slave
> is done with read/write then clock will not be stretched further, it
> will be released immediately.

Ah, now I see. This is a protection against the slave stretching the
clock forever. This makes sense.

> Hence I feel no harm in programming max timeout value.

I agree. "Random stretch" is just a bit confusing as a name. "Maximum"
would have been more clear IMO.


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