staging:iio:ad7887: Preallocate sample buffer

We know that the sample buffer will at most need to hold two 16 bit samples and
the 64 bit aligned 64 bit timestamp. Preallocate a buffer large enough to hold
this instead of allocating and freeing it each time a sample is read.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/staging/iio/adc/ad7887.h b/drivers/staging/iio/adc/ad7887.h
index 2e09e54fc9c..71e50925e06 100644
--- a/drivers/staging/iio/adc/ad7887.h
+++ b/drivers/staging/iio/adc/ad7887.h
@@ -72,9 +72,11 @@ struct ad7887_state {
         /*
          * DMA (thus cache coherency maintenance) requires the
          * transfer buffers to live in their own cache lines.
+         * Buffer needs to be large enough to hold two 16 bit samples and a
+         * 64 bit aligned 64 bit timestamp.
          */
-
-        unsigned char                   data[4] ____cacheline_aligned;
+        unsigned char data[ALIGN(4, sizeof(s64)) + sizeof(s64)]
+                ____cacheline_aligned;
 };
 
 enum ad7887_supported_device_ids {