use 64-bit arithmetic instead of 32-bit

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 <[email protected]>

---
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.

- Add code comment.

 drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

drivers/media/platform/vivid/vivid-cec.c +0 -0

index b55d278..614787b 100644
@@ -82,8 +82,15 @@ static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts,
 
 	if (adap == NULL)

drivers/media/platform/vivid/vivid-cec.c +2 -0

+	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);

Quoted 11 lines

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.

Quoted 7 lines

Addresses-Coverity-ID: 1454996

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
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

Quoted 12 lines

- Add code comment.

 drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

drivers/media/platform/vivid/vivid-cec.c +0 -0

index b55d278..614787b 100644
@@ -82,8 +82,15 @@ static void vivid_cec_pin_adap_events(struct  
 cec_adapter *adap, ktime_t ts,
 

drivers/media/platform/vivid/vivid-cec.c static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts, · line 91

Quoted 11 lines

drivers/media/platform/vivid/vivid-cec.c +7 -2

 	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

Quoted 6 lines

drivers/media/platform/vivid/vivid-cec.c +2 -0

+	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);

Hi Hans,

Quoting Hans Verkuil <[email protected]>:

Quoted 20 lines · Gustavo A. R. Silva

Quoted 11 lines

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.

Quoted 7 lines

Addresses-Coverity-ID: 1454996

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
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.

Quoted 2 lines

unncessary -> unnecessary

Thanks for this.

Quoted 13 lines

Quoted 13 lines

- Add code comment.

 drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

drivers/media/platform/vivid/vivid-cec.c +0 -0

index b55d278..614787b 100644
@@ -82,8 +82,15 @@ static void vivid_cec_pin_adap_events(struct  
 cec_adapter *adap, ktime_t ts,
 

Quoted 15 lines

drivers/media/platform/vivid/vivid-cec.c static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts, · line 91

Quoted 11 lines

drivers/media/platform/vivid/vivid-cec.c +7 -2

 	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:

In MHO the reason for the change is simply the discrepancy between the arithmetic expected by
the function ktime_sub_us and the arithmetic in which the expression is being evaluated. And this
has nothing to do with any particular tool.

Quoted 8 lines

/*
* 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.
*/

:P

In my opinion it is not a good idea to tie the code to a particular tool. There are only three appearances of the word 'Coverity' in the whole code base, and, honestly I don't want to add more.

So I think I will document this issue as a FP in the Coverity platform.

Quoted 59 lines

Hi Hans,

Quoting Hans Verkuil <[email protected]>:

Quoted 21 lines · Gustavo A. R. Silva

Quoted 11 lines

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.

Quoted 8 lines

Addresses-Coverity-ID: 1454996

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
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.

Quoted 2 lines

unncessary -> unnecessary

Thanks for this.

Quoted 13 lines

Quoted 13 lines

- Add code comment.

 drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

drivers/media/platform/vivid/vivid-cec.c +0 -0

index b55d278..614787b 100644
@@ -82,8 +82,15 @@ static void vivid_cec_pin_adap_events(struct
 cec_adapter *adap, ktime_t ts,
 

Quoted 15 lines

drivers/media/platform/vivid/vivid-cec.c static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts, · line 91

Quoted 11 lines

drivers/media/platform/vivid/vivid-cec.c +7 -2

 	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:

Quoted 5 lines

In MHO the reason for the change is simply the discrepancy between the arithmetic expected by
the function ktime_sub_us and the arithmetic in which the expression is being evaluated. And this
has nothing to do with any particular tool.

Hmm, you have a point.

OK, I've looked at the other patches in this patch series as well, and the only thing I would like to see changed is the 'Addresses-Coverity-ID' line in the patches: patch 4 says:

Addresses-Coverity-ID: 1324146 ("Unintentional integer overflow")

but that's the only one that mentions the specific coverity error. It would be nice if that can be added to the other patches as well so we have a record of the actual coverity error.

Quoted 11 lines

Quoted 8 lines

/*
* 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.
*/

:P

Quoted 5 lines

In my opinion it is not a good idea to tie the code to a particular tool. There are only three appearances of the word 'Coverity' in the whole code base, and, honestly I don't want to add more.

So I think I will document this issue as a FP in the Coverity platform.

FP?

Regards,

Hans

Quoted 11 lines · Gustavo A. R. Silva

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.

Quoted 7 lines

Addresses-Coverity-ID: 1454996

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
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

Quoted 12 lines

- Add code comment.

 drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

drivers/media/platform/vivid/vivid-cec.c +0 -0

index b55d278..614787b 100644
@@ -82,8 +82,15 @@ static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts,
 
 	if (adap == NULL)

drivers/media/platform/vivid/vivid-cec.c static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts, · line 91

Quoted 10 lines

drivers/media/platform/vivid/vivid-cec.c +7 -2

 		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.
*/