[PATCH 25/38] staging: media: davinci_vpfe: fix ipipe_mode type

[PATCH 25/38] staging: media: davinci_vpfe: fix ipipe_mode type

[Andrzej Hajda]

The variable can take negative values.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
---
 drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c b/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c
index 2a3a56b..b1d5e23 100644
--- a/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c
+++ b/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c
@@ -254,7 +254,7 @@ int config_ipipe_hw(struct vpfe_ipipe_device *ipipe)
 	void __iomem *ipipe_base = ipipe->base_addr;
 	struct v4l2_mbus_framefmt *outformat;
 	u32 color_pat;
-	u32 ipipe_mode;
+	int ipipe_mode;
 	u32 data_path;
 
 	/* enable clock to IPIPE */
-- 
1.9.1

Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types

[David Howells]

Andrzej Hajda <a.hajda@samsung.com> wrote:

> Semantic patch finds comparisons of types:
>     unsigned < 0
>     unsigned >= 0
> The former is always false, the latter is always true.
> Such comparisons are useless, so theoretically they could be
> safely removed, but their presence quite often indicates bugs.

Or someone has left them in because they don't matter and there's the
possibility that the type being tested might be or become signed under some
circumstances.  If the comparison is useless, I'd expect the compiler to just
discard it - for such cases your patch is pointless.

If I have, for example:

	unsigned x;

	if (x == 0 || x > 27)
		give_a_range_error();

I will write this as:

	unsigned x;

	if (x <= 0 || x > 27)
		give_a_range_error();

because it that gives a way to handle x being changed to signed at some point
in the future for no cost.  In which case, your changing the <= to an ==
"because the < part of the case is useless" is arguably wrong.

David

Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types

[Andrzej Hajda]

On 09/21/2015 03:42 PM, David Howells wrote:
> Andrzej Hajda <a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org> wrote:
> 
>> Semantic patch finds comparisons of types:
>>     unsigned < 0
>>     unsigned >= 0
>> The former is always false, the latter is always true.
>> Such comparisons are useless, so theoretically they could be
>> safely removed, but their presence quite often indicates bugs.
> 
> Or someone has left them in because they don't matter and there's the
> possibility that the type being tested might be or become signed under some
> circumstances.  If the comparison is useless, I'd expect the compiler to just
> discard it - for such cases your patch is pointless.
> 
> If I have, for example:
> 
> 	unsigned x;
> 
> 	if (x == 0 || x > 27)
> 		give_a_range_error();
> 
> I will write this as:
> 
> 	unsigned x;
> 
> 	if (x <= 0 || x > 27)
> 		give_a_range_error();
> 
> because it that gives a way to handle x being changed to signed at some point
> in the future for no cost.  In which case, your changing the <= to an ==
> "because the < part of the case is useless" is arguably wrong.

This is why I have not checked for such cases - I have skipped checks of type
	unsigned <= 0
exactly for the reasons above.

However I have left two other checks as they seems to me more suspicious - they
are always true or false. But as Dmitry and Andrew pointed out Linus have quite
strong opinion against removing range checks in such cases as he finds it
clearer. I think it applies to patches 29-36. I am not sure about patches 26-28,37.

Regards
Andrzej

> 
> David
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Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types

[Jacek Anaszewski]

On 09/22/2015 11:13 AM, Andrzej Hajda wrote:
> On 09/21/2015 03:42 PM, David Howells wrote:
>> Andrzej Hajda <a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org> wrote:
>>
>>> Semantic patch finds comparisons of types:
>>>      unsigned < 0
>>>      unsigned >= 0
>>> The former is always false, the latter is always true.
>>> Such comparisons are useless, so theoretically they could be
>>> safely removed, but their presence quite often indicates bugs.
>>
>> Or someone has left them in because they don't matter and there's the
>> possibility that the type being tested might be or become signed under some
>> circumstances.  If the comparison is useless, I'd expect the compiler to just
>> discard it - for such cases your patch is pointless.
>>
>> If I have, for example:
>>
>> 	unsigned x;
>>
>> 	if (x == 0 || x > 27)
>> 		give_a_range_error();
>>
>> I will write this as:
>>
>> 	unsigned x;
>>
>> 	if (x <= 0 || x > 27)
>> 		give_a_range_error();
>>
>> because it that gives a way to handle x being changed to signed at some point
>> in the future for no cost.  In which case, your changing the <= to an ==
>> "because the < part of the case is useless" is arguably wrong.
>
> This is why I have not checked for such cases - I have skipped checks of type
> 	unsigned <= 0
> exactly for the reasons above.
>
> However I have left two other checks as they seems to me more suspicious - they
> are always true or false. But as Dmitry and Andrew pointed out Linus have quite
> strong opinion against removing range checks in such cases as he finds it
> clearer. I think it applies to patches 29-36. I am not sure about patches 26-28,37.

Dropped 30/38 and 31/38 from LED tree then.

-- 
Best Regards,
Jacek Anaszewski

Re: [PATCH 25/38] staging: media: davinci_vpfe: fix ipipe_mode type

[Laurent Pinchart]

Hi Andrzej,

Thank you for the patch.

On Monday 21 September 2015 15:33:57 Andrzej Hajda wrote:
> The variable can take negative values.
> 
> The problem has been detected using proposed semantic patch
> scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].
> 
> [1]: http://permalink.gmane.org/gmane.linux.kernel/2038576
> 
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

and applied to my tree.

> ---
>  drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c
> b/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c index
> 2a3a56b..b1d5e23 100644
> --- a/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c
> +++ b/drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c
> @@ -254,7 +254,7 @@ int config_ipipe_hw(struct vpfe_ipipe_device *ipipe)
>  	void __iomem *ipipe_base = ipipe->base_addr;
>  	struct v4l2_mbus_framefmt *outformat;
>  	u32 color_pat;
> -	u32 ipipe_mode;
> +	int ipipe_mode;
>  	u32 data_path;
> 
>  	/* enable clock to IPIPE */

-- 
Regards,

Laurent Pinchart