linux-kernel - Re: [PATCH] i2c: bcm2835: Clear current message and count after a transaction

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Date:   Mon, 24 Dec 2018 09:54:48 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com, linux-i2c@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Ray Jui <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>,
        Eric Anholt <eric@...olt.net>,
        Stefan Wahren <stefan.wahren@...e.com>
Subject: Re: [PATCH] i2c: bcm2835: Clear current message and count after a
 transaction

Hi,

On Fri, 2018-12-21 at 09:52 -0800, Florian Fainelli wrote:
> On 12/21/18 4:11 AM, Paul Kocialkowski wrote:
> > The driver's interrupt handler checks whether a message is currently
> > being handled with the curr_msg pointer. When it is NULL, the interrupt
> > is considered to be unexpected. Similarly, the i2c_start_transfer
> > routine checks for the remaining number of messages to handle in
> > num_msgs.
> > 
> > However, these values are never cleared and always keep the message and
> > number relevant to the latest transfer (which might be done already and
> > the underlying message memory might have been freed).
> > 
> > When an unexpected interrupt hits with the DONE bit set, the isr will
> > then try to access the flags field of the curr_msg structure, leading
> > to a fatal page fault.
> > 
> > Fix the issue by systematically clearing curr_msg and num_msgs in the
> > driver-wide device structure when a transfer is considered complete.
> 
> Should not this get a Fixes tag?

Yes it totally should! Thanks for the suggestion.

Cheers,

Paul

> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > ---
> >  drivers/i2c/busses/i2c-bcm2835.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
> > index 44deae78913e..5486252f5f2f 100644
> > --- a/drivers/i2c/busses/i2c-bcm2835.c
> > +++ b/drivers/i2c/busses/i2c-bcm2835.c
> > @@ -298,6 +298,9 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
> >  		return -ETIMEDOUT;
> >  	}
> >  
> > +	i2c_dev->curr_msg = NULL;
> > +	i2c_dev->num_msgs = 0;
> > +
> >  	if (!i2c_dev->msg_err)
> >  		return num;
> >  
> > 
> 
> 
-- 
Paul Kocialkowski, Bootlin (formerly Free Electrons)
Embedded Linux and kernel engineering
https://bootlin.com