Re: [PATCH v1] Input: ads7846: ads7846_get_value - fix unaligned pointer value warning

On Fri, Sep 10, 2021 at 09:51:54AM +0200, Oleksij Rempel wrote:

Hi Dmitry,

On Thu, Sep 09, 2021 at 10:04:16PM -0700, Dmitry Torokhov wrote:

quoted

Hi Oleksij,

On Wed, Jul 07, 2021 at 02:41:15PM +0200, Oleksij Rempel wrote:

quoted

Fix warning reported by the kernel test robot:
drivers/input/touchscreen/ads7846.c:705:24: warning: taking address
of packed member 'data' of class or structure 'ads7846_buf' may result
in an unaligned pointer value [-Waddress-of-packed-member]

Fixes: 6965eece2a89 ("Input: ads7846 - convert to one message")
Reported-by: kernel test robot <redacted>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/input/touchscreen/ads7846.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index adb4c2230c31..1987dedac94f 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c

@@ -702,7 +702,7 @@ static int ads7846_get_value(struct ads7846_buf *buf)
 {
 	int value;
 
-	value = be16_to_cpup(&buf->data);
+	value = get_unaligned_be16(&buf->data);

ds7846_buf is declared as packed so I believe using be16_to_cpu(buf->data)
will suffice.

The pointer to the data is is off by 8 bits, so it is not naturally
aligned. This is why we need to use function which is dealing with
unaligned pointers. 

As I mentioned, the structure is packed, so the compiler will take care
of doing unaligned access safely on architectures that can not tolerate
it.

Thanks.

-- 
Dmitry