Re: [PATCH v3 1/2] v4l2: Add the polarity flags for parallel camera bus FIELD signal

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Hi Laurent,

On 09/21/2011 01:12 AM, Laurent Pinchart wrote:
> Hi Sylwester,
> 
> Thanks for the patch.
> 
> On Monday 19 September 2011 19:07:55 Sylwester Nawrocki wrote:
>> FIELD is an Even/Odd field selection signal, as specified in ITU-R BT.601
>> standard. Add corresponding flag for configuring the FIELD signal polarity.
>> Also add a comment about usage of V4L2_MBUS_[HV]SYNC* flags for the
>> hardware that uses [HV]REF signals.
> 
> I like this approach better.
> 
...
>> +/* Field selection signal for interlaced scan mode */
>> +#define V4L2_MBUS_FIELD_ACTIVE_HIGH		(1 << 10)
>> +#define V4L2_MBUS_FIELD_ACTIVE_LOW		(1 << 11)
> 
> What does this mean ? The FIELD signal is used to select between odd and even 
> fields. Does "active high" mean that the field is odd or even when the signal 
> has a high level ? The comment should make it explicit, or we could even 
> rename those two constants to FIELD_ODD_HIGH/FIELD_ODD_LOW (or 
> FIELD_EVEN_HIGH/FIELD_EVEN_LOW).

Yes, certainly I didn't think enough about this. I silently assumed that for
V4L2_MBUS_FIELD_ACTIVE_HIGH FIELD = 0 selects Field1 (odd) and FIELD = 1 selects
Field2 (even).
I think it would be good to construct the macro so it is possibly self-explanatory,
rather than requiring often to dig in the documentation.

So I would go for V4L2_MBUS_FIELD_ODD_LOW/V4L2_MBUS_FIELD_ODD_HIGH.
Unless someone proposes something different/better I'll send an amended version
tomorrow. 


Thanks,
-- 
Sylwester Nawrocki
Samsung Poland R&D Center
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