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From:   Andy Lutomirski <luto@kernel.org>
Date:   Sun, 5 Apr 2020 15:51:29 -0700
Message-ID: <CALCETrVUWEOwpMOLAPieU5mffaA6vJPWQov5N82gtcBo04JsyA@mail.gmail.com>
Subject: Re: [PATCH 0/1] i2c: imc: Add support for Intel iMC SMBus host controller.
To:     Stefan Schaeckeler <schaecsn@gmx.net>
Cc:     Wolfram Sang <wsa@the-dreams.de>,
        Andrew Lutomirski <luto@kernel.org>, linux-i2c@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Andy Shevchenko <andy.shevchenko@gmail.com>
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On Sun, Apr 5, 2020 at 2:41 PM Stefan Schaeckeler <schaecsn@gmx.net> wrote:
>
> Hello Wolfram,
>
> > > > This patch is based on Andy Lutomirski's iMC SMBus driver patch-set
> > > > https://lkml.org/lkml/2016/4/28/926. It never made it into the kernel. I hope
> > > > this rewrite will:
> > > >
> > > >
> > > > Overview
> > > >
> > > > Modern Intel memory controllers host an SMBus controller and connection to
> > > > DIMMs and their thermal sensors. The memory controller firmware has three modes
> > > > of operation: Closed Loop Thermal Throttling (CLTT), Open Loop Thermal
> > > > Throttling (OLTT) and none.
> > > >
> > > > - CLTT: The memory controller firmware is periodically accessing the DIMM
> > > >   temperature sensor over the SMBus.
> > > >
> > >
> > >
> > > I think this is great!  One question, though: what happens if the
> > > system is in CLTT mode but you disable CLTT and claim the bus for too
> > > long?  For example, if there's an infinite loop or other lockup which
> > > you have the tsod polling interval set to 0?  Does the system catch
> > > fire or does the system do something intelligent like temporarily
> > > switching to open loop?
> >
> > Any news on this question?
>
> Thank you for your interest in this patch. You can read my reply here
> https://lkml.org/lkml/2020/3/1/216

I think it could make sense to upstream this driver but to require a
scary boot-time option to enable it.  Maybe i2c_imc.dangerous=1?

>
>  Stefan