Input: ads7846 - make transfer buffers DMA safe

req.sample needs its own cacheline otherwise accessing req.msg fetches
it in again.

Note: This effect doesn't occur if the underlying SPI driver doesn't use
DMA at all.

Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index c24946f51256..ab51a8dbdb5a 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -281,17 +281,25 @@ struct ser_req {
         u8                      command;
         u8                      ref_off;
         u16                     scratch;
-        __be16                  sample;
         struct spi_message      msg;
         struct spi_transfer     xfer[6];
+        /*
+         * DMA (thus cache coherency maintenance) requires the
+         * transfer buffers to live in their own cache lines.
+         */
+        __be16 sample ____cacheline_aligned;
 };
 
 struct ads7845_ser_req {
         u8                      command[3];
         u8                      pwrdown[3];
-        u8                      sample[3];
         struct spi_message      msg;
         struct spi_transfer     xfer[2];
+        /*
+         * DMA (thus cache coherency maintenance) requires the
+         * transfer buffers to live in their own cache lines.
+         */
+        u8 sample[3] ____cacheline_aligned;
 };
 
 static int ads7846_read12_ser(struct device *dev, unsigned command)