linux-kernel - Re: [PATCH v3 09/11] i2c: npcm: Handle spurious interrupts

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Date:   Thu, 3 Mar 2022 14:48:20 +0200
From:   Tali Perry <tali.perry1@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Tyrone Ting <warp5tw@...il.com>, avifishman70@...il.com,
        Tomer Maimon <tmaimon77@...il.com>,
        Patrick Venture <venture@...gle.com>,
        Nancy Yuen <yuenn@...gle.com>,
        Benjamin Fair <benjaminfair@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        yangyicong@...ilicon.com, semen.protsenko@...aro.org,
        Wolfram Sang <wsa@...nel.org>, jie.deng@...el.com,
        sven@...npeter.dev, bence98@....bme.hu, lukas.bulwahn@...il.com,
        arnd@...db.de, olof@...om.net, Tali Perry <tali.perry@...oton.com>,
        Avi Fishman <Avi.Fishman@...oton.com>,
        tomer.maimon@...oton.com, KWLIU@...oton.com, JJLIU0@...oton.com,
        kfting@...oton.com, OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 09/11] i2c: npcm: Handle spurious interrupts

> On Thu, Mar 3, 2022 at 12:37 PM Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > On Thu, Mar 03, 2022 at 04:31:39PM +0800, Tyrone Ting wrote:
> > > From: Tali Perry <tali.perry1@...il.com>
> > >
> > > In order to better handle spurious interrupts:
> > > 1. Disable incoming interrupts in master only mode.
> > > 2. Clear end of busy (EOB) after every interrupt.
> > > 3. Return correct status during interrupt.
> >
> > This is bad commit message, it doesn't explain "why" you are doing these.
> >
> > ...


BMC users connect a huge tree of i2c devices and muxes.
This tree suffers from spikes, noise and double clocks.
All these may cause spurious interrupts to the BMC.

If the driver gets an IRQ which was not expected and was not handled
by the IRQ handler,
there is nothing left to do but to clear the interrupt and move on.
If the transaction failed, driver has a recovery function.
After that, user may retry to send the message.

Indeed the commit message doesn't explain all this.
We will fix and add to the next patchset.


> >
> > > +     /*
> > > +      * if irq is not one of the above, make sure EOB is disabled and all
> > > +      * status bits are cleared.
> >
> > This does not explain why you hide the spurious interrupt.
> >
> > > +      */
> > > +     if (ret == IRQ_NONE) {
> > > +             npcm_i2c_eob_int(bus, false);
> > > +             npcm_i2c_clear_master_status(bus);
> > > +     }
> > > +
> > > +     return IRQ_HANDLED;
> >
> > --
> > With Best Regards,
> > Andy Shevchenko
> >
> >

Thanks Andy,

BR,
Tali Perry