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Date:   Wed, 5 Aug 2020 11:17:25 +0200
From:   Wolfram Sang <wsa@kernel.org>
To:     Ray Jui <ray.jui@broadcom.com>
Cc:     Dhananjay Phadke <dphadke@linux.microsoft.com>,
        Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ray Jui <rjui@broadcom.com>,
        bcm-kernel-feedback-list@broadcom.com
Subject: Re: [PATCH] i2c: iproc: fix race between client unreg and isr
Message-ID: <20200805091725.GI1229@kunai>
Mail-Followup-To: Wolfram Sang <wsa@kernel.org>,
        Ray Jui <ray.jui@broadcom.com>,
        Dhananjay Phadke <dphadke@linux.microsoft.com>,
        Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ray Jui <rjui@broadcom.com>, bcm-kernel-feedback-list@broadcom.com
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On Mon, Jul 27, 2020 at 01:43:40PM -0700, Ray Jui wrote:
>=20
>=20
> On 7/27/2020 1:26 PM, Wolfram Sang wrote:
> > On Mon, Jul 27, 2020 at 08:13:46PM +0200, Wolfram Sang wrote:
> >>
> >>> Can you confirm that even if we have irq pending at the i2c IP core
> >>> level, as long as we execute Step 2. below (to disable/mask all slave
> >>> interrupts), after 'enable_irq' is called, we still will not receive =
any
> >>> further i2c slave interrupt?
> >>
> >> This is HW dependant. From my tests with Renesas HW, this is not the
> >> case. But the actual error case was impossible to trigger for me, so
> >> far. I might try again later. But even in the worst case, I would only
> >> get a "spurious interrupt" and not an NULL-ptr OOPS.
> >=20
> > Let me explain how I verified this:
> >=20
> > 0) add a debug print whenever the slave irq part is called
> >=20
> > 1) Put a 2 second delay after disable_irq() and before clearing
> > interrupt enable register
> >=20
> > 2) unbind the slave driver in the background, triggering the 2s delay
> >=20
> > 3) during the delay, try to read from the to-be-unbound slave in the
> >    foreground
> >=20
> > 4) ensure there is no prinout from the slave irq
> >=20
> > Worked fine for me with the Renesas R-Car I2C IP interface. As mentioned
> > before, I couldn't trigger a bad case with my setup. So, I hope this new
> > fix will work for Rayagonda's test case, too!
> >=20
>=20
> Sure. I suggest Dhananjay gives the sequence you proposed here a try
> (with delay added during the testing to widen the window to cover corner
> cases). If it works, we can just go with your proposed sequence here.

Any progress yet?


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