linux-kernel - Re: [PATCH v5 3/6] i2c: npcm: Modify timeout evaluation mechanism

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Message-ID: <CACD3sJYhAYV3zBse5ntFsQmLV+TpLKtOiyyqgp3g8qeja54Ejw@mail.gmail.com>
Date: Wed, 9 Oct 2024 13:49:16 +0800
From: Tyrone Ting <warp5tw@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: avifishman70@...il.com, tmaimon77@...il.com, tali.perry1@...il.com, 
	venture@...gle.com, yuenn@...gle.com, benjaminfair@...gle.com, 
	andi.shyti@...nel.org, wsa@...nel.org, rand.sec96@...il.com, 
	wsa+renesas@...g-engineering.com, tali.perry@...oton.com, 
	Avi.Fishman@...oton.com, tomer.maimon@...oton.com, KWLIU@...oton.com, 
	JJLIU0@...oton.com, kfting@...oton.com, openbmc@...ts.ozlabs.org, 
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/6] i2c: npcm: Modify timeout evaluation mechanism

Hi Andy:

Thank you for your comments.

Andy Shevchenko <andriy.shevchenko@...ux.intel.com> 於 2024年10月1日 週二 下午9:14寫道：
>
> On Tue, Oct 01, 2024 at 02:28:52PM +0800, Tyrone Ting wrote:
> > From: Tyrone Ting <kfting@...oton.com>
> >
> > The users want to connect a lot of masters on the same bus.
> > This timeout is used to determine the time it takes to take bus ownership.
> > The transactions are very long, so waiting 35ms is not enough.
> >
> > Increase the timeout and treat it as the total timeout, including retries.
> > The total timeout is 2 seconds now.
> >
> > The i2c core layer will have chances to retry to call the i2c driver
> > transfer function if the i2c driver reports that the bus is busy and
> > returns EAGAIN.
>
> -EAGAIN
>
> ...
>
> > +             /*
> > +              * Adaptive TimeOut: estimated time in usec + 100% margin:
> > +              * 2: double the timeout for clock stretching case
> > +              * 9: bits per transaction (including the ack/nack)
> > +              */
> > +             timeout_usec = (2 * 9 * USEC_PER_SEC / bus->bus_freq) * (2 + nread + nwrite);
>
> Side note (as I see it was in the original code), from physics
> point of view the USEC_PER_SEC here should be simply MICRO
> (as 1/Hz == s, and here it will be read as s^2 in the result),
> but if one finds the current more understandable, okay then.
>

I just check with Nuvoton members and they prefer the USEC_PER_SEC way.

> --
> With Best Regards,
> Andy Shevchenko
>
>

Thank you.

Regards,
Tyrone