linux-kernel - [PATCH 4.9 172/175] iio:pressure:mpl3115: Force alignment of buffer

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Message-Id: <20201228124901.562817115@linuxfoundation.org>
Date:   Mon, 28 Dec 2020 13:50:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Peter Meerwald <pmeerw@...erw.net>, Stable@...r.kernel.org
Subject: [PATCH 4.9 172/175] iio:pressure:mpl3115: Force alignment of buffer

From: Jonathan Cameron <Jonathan.Cameron@...wei.com>

commit 198cf32f0503d2ad60d320b95ef6fb8243db857f upstream.

Whilst this is another case of the issue Lars reported with
an array of elements of smaller than 8 bytes being passed
to iio_push_to_buffers_with_timestamp(), the solution here is
a bit different from the other cases and relies on __aligned
working on the stack (true since 4.6?)

This one is unusual.  We have to do an explicit memset() each time
as we are reading 3 bytes into a potential 4 byte channel which
may sometimes be a 2 byte channel depending on what is enabled.
As such, moving the buffer to the heap in the iio_priv structure
doesn't save us much.  We can't use a nice explicit structure
on the stack either as the data channels have different storage
sizes and are all separately controlled.

Fixes: cc26ad455f57 ("iio: Add Freescale MPL3115A2 pressure / temperature sensor driver")
Reported-by: Lars-Peter Clausen <lars@...afoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc: Peter Meerwald <pmeerw@...erw.net>
Cc: <Stable@...r.kernel.org>
Link: https://lore.kernel.org/r/20200920112742.170751-7-jic23@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/iio/pressure/mpl3115.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/iio/pressure/mpl3115.c
+++ b/drivers/iio/pressure/mpl3115.c
@@ -139,7 +139,14 @@ static irqreturn_t mpl3115_trigger_handl
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct mpl3115_data *data = iio_priv(indio_dev);
-	u8 buffer[16]; /* 32-bit channel + 16-bit channel + padding + ts */
+	/*
+	 * 32-bit channel + 16-bit channel + padding + ts
+	 * Note that it is possible for only one of the first 2
+	 * channels to be enabled. If that happens, the first element
+	 * of the buffer may be either 16 or 32-bits.  As such we cannot
+	 * use a simple structure definition to express this data layout.
+	 */
+	u8 buffer[16] __aligned(8);
 	int ret, pos = 0;
 
 	mutex_lock(&data->lock);