patch "iio:pressure:mpl3115: Force alignment of buffer" added to staging-next

patch "iio:pressure:mpl3115: Force alignment of buffer" added to staging-next

[gregkh]

This is a note to let you know that I've just added the patch titled

    iio:pressure:mpl3115: Force alignment of buffer

to my staging git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.


From 198cf32f0503d2ad60d320b95ef6fb8243db857f Mon Sep 17 00:00:00 2001
From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Date: Sun, 20 Sep 2020 12:27:40 +0100
Subject: iio:pressure:mpl3115: Force alignment of buffer

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@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: Peter Meerwald <pmeerw@pmeerw.net>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200920112742.170751-7-jic23@kernel.org
---
 drivers/iio/pressure/mpl3115.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/pressure/mpl3115.c b/drivers/iio/pressure/mpl3115.c
index ccdb0b70e48c..1eb9e7b29e05 100644
--- a/drivers/iio/pressure/mpl3115.c
+++ b/drivers/iio/pressure/mpl3115.c
@@ -144,7 +144,14 @@ static irqreturn_t mpl3115_trigger_handler(int irq, void *p)
 	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);
-- 
2.29.2