Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] i2c: iproc: fix race between client unreg and isr
To:     Wolfram Sang <wsa@kernel.org>
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
References: <1595115599-100054-1-git-send-email-dphadke@linux.microsoft.com>
 <116ac90c-8b49-ca89-90a4-9a28f43a7c50@broadcom.com>
 <20200722104128.GK1030@ninjato>
 <5048cf44-e2c2-ee31-a9fb-b823f16c2c7d@broadcom.com>
 <20200725101815.GA1519@ninjato>
 <4cf12c92-889d-ffbf-f8de-c1e08cfb8ce9@broadcom.com>
 <20200727181346.GA1034@ninjato> <20200727202657.GA18997@ninjato>
From:   Ray Jui <ray.jui@broadcom.com>
Message-ID: <f56b0f2c-f723-a4b6-8c03-4b397aaa375c@broadcom.com>
Date:   Mon, 27 Jul 2020 13:43:40 -0700
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20200727202657.GA18997@ninjato>
Content-Type: text/plain; charset=windows-1252
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


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.
> 
> Let me explain how I verified this:
> 
> 0) add a debug print whenever the slave irq part is called
> 
> 1) Put a 2 second delay after disable_irq() and before clearing
> interrupt enable register
> 
> 2) unbind the slave driver in the background, triggering the 2s delay
> 
> 3) during the delay, try to read from the to-be-unbound slave in the
>    foreground
> 
> 4) ensure there is no prinout from the slave irq
> 
> 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!
> 

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.

Thanks!

Ray