Re: [PATCH RFC] staging: comedi: dt282x: condition with no effect - if identical to else

[Nicholas Mc Guire <der.herr@hofr.at>]

On Tue, 03 Feb 2015, Ian Abbott wrote:

> On 03/02/15 12:38, Nicholas Mc Guire wrote:
>> The if and the else branch code are identical - so the condition has no
>> effect on the effective code - this patch removes the condition and the
>> duplicated code.
>>
>> Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
>> ---
>>
>> The if and else branch are identical code thus the condition has no effect
>>
>>      if (cmd->scan_begin_src == TRIG_FOLLOW) {
>>              /* internal trigger */
>>              err |= cfc_check_trigger_arg_is(&cmd->scan_begin_arg, 0);
>>      } else {
>>              /* external trigger */
>>              /* should be level/edge, hi/lo specification here */
>>              err |= cfc_check_trigger_arg_is(&cmd->scan_begin_arg, 0);
>>      }
>>
>> As the comments indicate that they are serving different purposes this
>> looks like a bug. In any case - if intentional - it would need some
>> comments on why.
>>
>> This needs a review by someone that knows the details of this driver.
>> Also not sure about the retained comment string if that is still valid now.
>>
>> Patch was only compile tested for x86_64_defconfig + CONFIG_STAGING=y
>> CONFIG_COMEDI=m, COMEDI_ISA_DRIVERS=y, CONFIG_COMEDI_DT282X=m
>>
>> Patch is against 3.0.19-rc7 (localversion = -next-20150203)
>>
>>   drivers/staging/comedi/drivers/dt282x.c |   10 ++--------
>>   1 file changed, 2 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/staging/comedi/drivers/dt282x.c b/drivers/staging/comedi/drivers/dt282x.c
>> index 051dfb2..22c59e5 100644
>> --- a/drivers/staging/comedi/drivers/dt282x.c
>> +++ b/drivers/staging/comedi/drivers/dt282x.c
>> @@ -685,14 +685,8 @@ static int dt282x_ai_cmdtest(struct comedi_device *dev,
>>
>>   	err |= cfc_check_trigger_arg_is(&cmd->start_arg, 0);
>>
>> -	if (cmd->scan_begin_src == TRIG_FOLLOW) {
>> -		/* internal trigger */
>> -		err |= cfc_check_trigger_arg_is(&cmd->scan_begin_arg, 0);
>> -	} else {
>> -		/* external trigger */
>> -		/* should be level/edge, hi/lo specification here */
>
> I think what that comment means is that it should allow scan_begin_arg  
> to have various combinations of the CR_EDGE and CR_INVERT bits set. I.e. 
> it ought to allow whatever combination of CR_EDGE and CR_INVERT better 
> describes the nature of the external trigger signal, in addition to 
> allowing the lazy default value 0.
>
> I don't know what the nature of the external trigger signal is, as I  
> haven't seen the manual.  I think Hartley might have seen one.
>
>> -		err |= cfc_check_trigger_arg_is(&cmd->scan_begin_arg, 0);
>> -	}
>> +	/* internal trigger */
>
> That comment would be misleading as it could be an internal or external  
> trigger.
>

yup - was unsure on what to put there (if any).

>
> If you want to apply this patch, remove that comment first.  But I'd
> rather leave the existing code there as a reminder.
>

if that is the preferred solution maybe someone with suitable
knowledge could add a comment in the else case explaining why
it is the same or at least making it clear that it is an
intentional placeholder.

>> +    err |= cfc_check_trigger_arg_is(&cmd->scan_begin_arg, 0);
>>
>>      err |= cfc_check_trigger_arg_min(&cmd->convert_arg, 4000);
>>
>>
>
thanks for your review comments!

thx!
hofrat