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From:   Benjamin Tissoires <benjamin.tissoires@redhat.com>
Date:   Tue, 30 Oct 2018 15:34:51 +0100
Message-ID: <CAO-hwJ+B5iUpbUamsCfNKGwxJMM9fNBUnrb2-csn1VpNG58KBA@mail.gmail.com>
Subject: Re: [PATCH 2/2] i2c: Clear client->irq in i2c_device_remove
To:     ckeepax@opensource.cirrus.com
Cc:     Wolfram Sang <wsa@the-dreams.de>,
        Linux I2C <linux-i2c@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        patches@opensource.cirrus.com
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On Tue, Oct 30, 2018 at 12:51 PM Charles Keepax
<ckeepax@opensource.cirrus.com> wrote:
>
> On Mon, Oct 29, 2018 at 11:15:47AM +0100, Benjamin Tissoires wrote:
> > On Sun, Oct 28, 2018 at 11:31 PM Wolfram Sang <wsa@the-dreams.de> wrote:
> > >
> > > On Fri, Oct 19, 2018 at 09:59:58AM +0100, Charles Keepax wrote:
> > > > The IRQ will be mapped in i2c_device_probe only if client->irq is zero and
> > > > i2c_device_remove does not clear this. When rebinding an I2C device,
> > > > whos IRQ provider has also been rebound this means that an IRQ mapping
> > > > will never be created, causing the I2C device to fail to acquire its
> > > > IRQ. Fix this issue by clearing client->irq in i2c_device_remove,
> > > > forcing i2c_device_probe to lookup the mapping again.
> > > >
> > > > Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
> > >
> > > Adding Benjamin here again. Also, should there be a Fixes: tag?
> >
> > Not sure if the circumstances are preventing me to think straight, but
> > how can you reprobe the i2c_device?
>
> You just head into /sys/bus/i2c/drivers/<the_driver> and use the
> unbind file to remove the driver. You can then probe the driver
> again using the bind file.

Right... not sure why I haven't seen that one yesterday

>
> > And in all cases, for the Host notify part, having the IRQ already set
> > shouldn't be an issue.
>
> To be clear this isn't a theoretical issue this is something I
> can replicate very easily. The problem comes in when you unbind
> both the I2C device and the device that is providing its IRQ. In
> my case the I2C device is a speaker amp and the device providing
> IRQs is an audio CODEC.
>
> When the device providing the IRQ is unbound it will delete the
> IRQ mapping. For the I2C device to acquire its IRQ something
> needs to recreate that mapping, this would normally happen (in a
> DT system) as a result of the of_irq_get/_by_name. But as
> client->irq is already set this doesn't happen, causing the I2C
> device to fail probe because it couldn't locate its IRQ.

Right. I completely missed the fact that the driver of the IRQ could
be reset during the period the device is unbound.
That's a pretty strong case for this patch.

>
> I can provide some stack traces or something if that would help
> to clarify the issue?

No, that's fine. Now I get this, and I totally agree with the approach:

Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

Cheers,
Benjamin