drm/i2c/tda998x: Fix signed overflow issue
This is C standard hair-splitting, but afaict
- sum will be promoted to signed int in computation since
uint8_t fits
- signed overflow is undefined.
No we need to add up an awful lot of bytes to actually make it
overflow. But I guess the real risk is gcc spotting this and going
bananas. Fix this by simply using unsigned in to force all computations
to use the well-defined unsigned behaviour.
Spotted by coverity.
v2: Simplify the entire computation as suggested by Jean.
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Jean-Francois Moine <moinejf@free.fr>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
index 48af5ca..240c331 100644
--- a/drivers/gpu/drm/i2c/tda998x_drv.c
+++ b/drivers/gpu/drm/i2c/tda998x_drv.c
@@ -568,11 +568,11 @@
static uint8_t tda998x_cksum(uint8_t *buf, size_t bytes)
{
- uint8_t sum = 0;
+ int sum = 0;
while (bytes--)
- sum += *buf++;
- return (255 - sum) + 1;
+ sum -= *buf++;
+ return sum;
}
#define HB(x) (x)