On 02/05/2018 09:36 PM, Gustavo A. R. Silva wrote: > Add suffix ULL to constant 10 in order to give the compiler complete > information about the proper arithmetic to use. Notice that this > constant is used in a context that expects an expression of type > u64 (64 bits, unsigned). > > The expression len * 10 * CEC_TIM_DATA_BIT_TOTAL is currently being > evaluated using 32-bit arithmetic. > > Also, remove unnecessary parentheses and add a code comment to make it > clear what is the reason of the code change. > > Addresses-Coverity-ID: 1454996 > Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx> > --- > Changes in v2: > - Update subject and changelog to better reflect the proposed code changes. > - Add suffix ULL to constant instead of casting a variable. > - Remove unncessary parentheses. unncessary -> unnecessary > - Add code comment. > > drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/platform/vivid/vivid-cec.c b/drivers/media/platform/vivid/vivid-cec.c > index b55d278..614787b 100644 > --- a/drivers/media/platform/vivid/vivid-cec.c > +++ b/drivers/media/platform/vivid/vivid-cec.c > @@ -82,8 +82,15 @@ static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts, > > if (adap == NULL) > return; > - ts = ktime_sub_us(ts, (CEC_TIM_START_BIT_TOTAL + > - len * 10 * CEC_TIM_DATA_BIT_TOTAL)); > + > + /* > + * Suffix ULL on constant 10 makes the expression > + * CEC_TIM_START_BIT_TOTAL + 10ULL * len * CEC_TIM_DATA_BIT_TOTAL > + * be evaluated using 64-bit unsigned arithmetic (u64), which > + * is what ktime_sub_us expects as second argument. > + */ That's not really the comment that I was looking for. It still doesn't explain *why* this is needed at all. How about something like this: /* * Add the ULL suffix to the constant 10 to work around a false Coverity * "Unintentional integer overflow" warning. Coverity isn't smart enough * to understand that len is always <= 16, so there is no chance of an * integer overflow. */ Regards, Hans > + ts = ktime_sub_us(ts, CEC_TIM_START_BIT_TOTAL + > + 10ULL * len * CEC_TIM_DATA_BIT_TOTAL); > cec_queue_pin_cec_event(adap, false, ts); > ts = ktime_add_us(ts, CEC_TIM_START_BIT_LOW); > cec_queue_pin_cec_event(adap, true, ts); >
