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 at arm.linux.org.uk>
Cc: Rob Clark <robdclark at gmail.com>
Cc: Jean-Francois Moine <moinejf at free.fr>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
drivers/gpu/drm/i2c/tda998x_drv.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c
b/drivers/gpu/drm/i2c/tda998x_drv.c
index 48af5cac1902..240c331405b9 100644
--- a/drivers/gpu/drm/i2c/tda998x_drv.c
+++ b/drivers/gpu/drm/i2c/tda998x_drv.c
@@ -568,11 +568,11 @@ static irqreturn_t tda998x_irq_thread(int irq, void *data)
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)
--
1.8.5.2
