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From:   Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To:     bcm-kernel-feedback-list@broadcom.com, linux-i2c@vger.kernel.org,
        linux-rpi-kernel@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Florian Fainelli <f.fainelli@gmail.com>,
        Ray Jui <rjui@broadcom.com>,
        Scott Branden <sbranden@broadcom.com>,
        Eric Anholt <eric@anholt.net>,
        Stefan Wahren <stefan.wahren@i2se.com>,
        Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Subject: [PATCH] i2c: bcm2835: Clear current message and count after a transaction
Date:   Fri, 21 Dec 2018 13:11:35 +0100
Message-Id: <20181221121135.4847-1-paul.kocialkowski@bootlin.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.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;
 
-- 
2.20.1