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>

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index c24946f..ab51a8d 100644 (file)
--- 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)