[RFC PATCH 4/4] iio: imu: adis16400: Fix buffer alignment requirements.

From: Jonathan Cameron <jic23@kernel.org>
To: linux-iio@vger.kernel.org
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Nuno Sa <nuno.sa@analog.com>
Subject: [RFC PATCH 4/4] iio: imu: adis16400: Fix buffer alignment requirements.
Date: Sat,  1 May 2021 18:25:15 +0100	[thread overview]
Message-ID: <20210501172515.513486-5-jic23@kernel.org> (raw)
In-Reply-To: <20210501172515.513486-1-jic23@kernel.org>

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

iio_push_to_buffers_with_timestamp() requires that the buffer
is 8 byte alignment to ensure an inserted timestamp is naturally aligned.

This requirement was not met here when burst mode is in use beause
of a leading u16. Use the new iio_push_to_buffers_with_ts_na() function
that has more relaxed requirements.

It is somewhat complex to access that actual data length, but a
safe bound can be found by using scan_bytes - sizeof(timestamp) so that
is used in this path.

More efficient approaches exist, but this ensure correctness at the
cost of using a bounce buffer.

Fixes: 5075e0720d93 ("iio: imu: adis: generalize burst mode support")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/imu/adis16400.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/imu/adis16400.c b/drivers/iio/imu/adis16400.c
index 768aa493a1a6..c6d03a37373b 100644
--- a/drivers/iio/imu/adis16400.c
+++ b/drivers/iio/imu/adis16400.c
@@ -663,13 +663,23 @@ static irqreturn_t adis16400_trigger_handler(int irq, void *p)
 		spi_setup(st->adis.spi);
 	}
 
-	if (st->variant->flags & ADIS16400_BURST_DIAG_STAT)
+	if (st->variant->flags & ADIS16400_BURST_DIAG_STAT) {
 		buffer = adis->buffer + sizeof(u16);
-	else
-		buffer = adis->buffer;
+		/*
+		 * The size here is always larger than, or equal to the true
+		 * size of the channel data. This may result in a larger copy
+		 * than necessary, but as the target buffer will be
+		 * buffer->scan_bytes this will be safe.
+		 */
+		iio_push_to_buffers_with_ts_na(indio_dev, buffer,
+					       indio_dev->scan_bytes - sizeof(pf->timestamp),
+					       pf->timestamp);
+	} else {
+		iio_push_to_buffers_with_timestamp(indio_dev,
+						   adis->buffer,
+						   pf->timestamp);
+	}
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
-		pf->timestamp);
 
 	iio_trigger_notify_done(indio_dev->trig);
 
-- 
2.31.1

