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

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Date:   Thu, 3 Mar 2022 16:13:34 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Tali Perry <tali.perry1@...il.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 03, 2022 at 02:48:20PM +0200, Tali Perry wrote:
> > 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.

Yes, the problem is what "move on" means in your case.
If you get a spurious interrupts there are possibilities what's wrong:
1) HW bug(s)
2) FW bug(s)
3) Missed IRQ mask in the driver
4) Improper IRQ mask in the driver

The below approach seems incorrect to me.

> 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